Measurement of the Soft-Drop Jet Mass in pp Collisions at s=13  TeV with the ATLAS Detector

Jet substructure observables have significantly extended the search program for physics beyond the standard model at the Large Hadron Collider. The state-of-the-art tools have been motivated by the ...

Search for the Higgs Boson in theH→WW(*)→l+νl−ν¯Decay Channel inppCollisions ats=7  TeVwith the ATLAS Detector

A search for the Higgs boson has been performed in the H -> WW(*()) -> l+vl-(v) over bar channel (l = e/mu) with an integrated luminosity of 2.05 fb(-1) of pp collisions at root s = 7 TeV collected with the ATLAS detector at the Large Hadron Collider. No significant excess of events over the expected background is observed and limits on the Higgs boson production cross section are derived for a Higgs boson mass in the range 110 GeV< m(H) < 300 GeV. The observations exclude the presence of a standard model Higgs boson with a mass 145 < m(H) < 206 GeV at 95% confidence level.

Determination of the LEP centre-of-mass energy from Zγ events

Radiative returns to the Z resonance (Zgamma events) are used to determine the LEP2 centre-of-mass energy from the data collected with the ALEPH detector in 1997. The average centre-of-mass energy is measured to be: E_CM = 182.50 +- 0.19(stat) +- 0.08(syst) GeV in good agreement with the precise determination by the LEP energy working group of 182.652 +- 0.050 GeV. If applied to the measurement of the W mass, its precision translates into a systematic error on M_W which is smaller than the statistical error achieved from the corresponding dataset.

Search for new phenomena in the WW→lνl′ν′ final state in pp collisions at s=7TeV with the ATLAS detector

This Letter reports a search for a heavy particle that decays to WW using events produced in pp collisions at root s = 7 TeV. The data were recorded in 2011 by the ATLAS detector and correspond to an integrated luminosity of 4.7 fb(-1). WW -> lvl'v' (l,l' = e or mu) final states are considered and the distribution of the transverse mass of the W W candidates is found to be consistent with Standard Model expectations. Upper limits on the production cross section times branching ratio into W boson pairs are set for Randall-Sundrum and bulk Randall-Sundrum gravitons, which result in observed 95% CL lower limits on the masses of the two particles of 1.23 TeV and 0.84 TeV, respectively.

Measurement of the W→τντ cross section in pp collisions at s=7 TeV with the ATLAS experiment

The cross section for the production of W bosons with subsequent decay W to tau nu is measured with the ATLAS detector at the LHC. The analysis is based on a data sample that was recorded in 2010 at a proton-proton center-of-mass energy of sqrt(s) = 7 TeV and corresponds to an integrated luminosity of 34 pb^-1. The cross section is measured in a region of high detector acceptance and then extrapolated to the full phase space. The product of the total W production cross section and the W to tau nu branching ratio is measured to be 11.1 +/- 0.3 (stat) +/- 1.7 (syst) +/- 0.4 (lumi) nb.

Performance of jet substructure techniques for large-$R$ jets in proton-proton collisions at $\sqrt{s}$ = 7 TeV using the ATLAS detector

This paper presents the application of a variety of techniques to study jet substructure. The performance of various modified jet algorithms, or jet grooming techniques, for several jet types and event topologies is investigated for jets with transverse momentum larger than 300 GeV. Properties of jets subjected to the mass-drop filtering, trimming, and pruning algorithms are found to have a reduced sensitivity to multiple proton-proton interactions, are more stable at high luminosity and improve the physics potential of searches for heavy boosted objects. Studies of the expected discrimination power of jet mass and jet substructure observables in searches for new physics are also presented.…

Updated measurement of the τ lepton lifetime

A new measurement of the mean lifetime of the tau lepton is presented. Three different analysis methods are applied to a sample of 90000 tau pairs, collected in 1993 and 1994 with the ALEPH detector at LEP. The average of this measurement and those previously published by ALEPH is tau_tau = 290.1 +- 1.5 +- 1.1 fs.

Studies of Quantum Chromodynamics with the ALEPH Detector

Previously published and as vet unpublished QCD results obtained with the ALEPH detector at LEP1 are presented. The unprecedented statistics allows detailed studies of both perturbative and non-perturbative aspects of strong interactions to be carried out using hadronic Z and tau decays. The studies presented include precise determinations of the strong coupling constant. tests of its flavour independence, tests of the SU(3) gauge structure of QCD, study of coherence effects, and measurements of single-particle inclusive distributions and two-particle correlations for many identified baryons and mesons. (C) 1998 Elsevier Science B.V.

Search for light top squark pair production in final states with leptons and b-jets with the ATLAS detector in s=7 TeV proton–proton collisions

The results of a search for pair production of light top squarks are presented, using 4.7 fb(-1) of root s = 7 TeV proton-proton collisions collected with the ATLAS detector at the Large Hadron Collider. This search targets top squarks with masses similar to, or lighter than, the top quark mass. Final states containing exclusively one or two leptons (e, mu), large missing transverse momentum, light-flavour jets and b-jets are used to reconstruct the top squark pair system. Event-based mass scale variables are used to separate the signal from a large t (t) over bar background. No excess over the Standard Model expectations is found. The results are interpreted in the framework of the Minimal…

Search for squarks and gluinos in final states with jets and missing transverse momentum using 36  fb−1 of s=13  TeV pp collision data with the ATLAS detector

A search for the supersymmetric partners of quarks and gluons (squarks and gluinos) in final states containing hadronic jets and missing transverse momentum, but no electrons or muons, is presented ...

Measurement of the charge asymmetry in top quark pair production in pp collisions at root s=7 TeV using the ATLAS detector

A measurement of the top-antitop production charge asymmetry A[subscript C] is presented using data corresponding to an integrated luminosity of 1.04 fb[superscript −1] of pp collisions at s√=7 TeV collected by the ATLAS detector at the LHC. Events are selected with a single lepton (electron or muon), missing transverse momentum and at least four jets of which at least one jet is identified as coming from a b-quark. A kinematic fit is used to reconstruct the t[bar over t] event topology. After background subtraction, a Bayesian unfolding procedure is performed to correct for acceptance and detector effects. The measured value of A[subscript C] is A[subscript C]=−0.019±0.028 (stat.)±0.024 (s…

Improved tau polarisation measurement

Using 22 pb−1 of data collected at LEP in 1992 on the peak of the Z resonance, the ALEPH collaboration has measured the polarisation of the tau leptons decaying into $$ev\bar v, \mu v\bar v$$ ,πν, ρν and a1 ν from their individual decay product distributions. The measurement of the tau polarisation as a function of the production polar angle yields the two parametersN τ andN e, where, in terms of the axial and vector couplingsg Al andg Vl,N l=2g Vl gAl/(g Vl 2 +g 2 ). This analysis follows to a large extent the methods devised for the 1990 and 1991 data but with improvements which bring a better understanding of the systematic uncertainties. Combining the 1992 measurements with our previous…

Measurement of the flavour composition of dijet events in pp collisions at √s = 7 TeV with the ATLAS detector

This paper describes a measurement of the flavour composition of dijet events produced in pp collisions at s√=7~TeVs=7~TeV using the ATLAS detector. The measurement uses the full 2010 data sample, corresponding to an integrated luminosity of 39 pb−1. Six possible combinations of light, charm and bottom jets are identified in the dijet events, where the jet flavour is defined by the presence of bottom, charm or solely light flavour hadrons in the jet. Kinematic variables, based on the properties of displaced decay vertices and optimised for jet flavour identification, are used in a multidimensional template fit to measure the fractions of these dijet flavour states as functions of the leadin…

Measurement of the differential cross-sections of inclusive, prompt and non-prompt J/ψ production in proton–proton collisions at s=7 TeV

The inclusive J/psi production cross-section and fraction of J/psi mesons produced in B-hadron decays are measured in proton proton collisions at root s = 7 TeV with the ATLAS detector at the LHC, as a function of the transverse momentum and rapidity of the J/psi, using 2.3 pb(-1) of integrated luminosity. The cross-section is measured from a minimum P-T of 1 GeV to a maximum of 70 GeV and for rapidities within vertical bar y vertical bar < 2.4 giving the widest reach of any measurement of J/psi production to date. The differential production cross-sections of prompt and non-prompt J/psi are separately determined and are compared to Colour Singlet NNLO*, Colour Evaporation Model, and FONLL …

Search for a Standard Model Higgs boson in the mass range 200–600 GeV in the H→ZZ→ℓ+ℓ−qq¯ decay channel with the ATLAS detector

A search for a heavy Standard Model Higgs boson decaying via H -> ZZ -> l(+)l(-)q (q) over bar, where l = e or mu, is presented. The search uses a data set of pp collisions at root s = 7 TeV, ...

Measurement of the top quark pair production cross-section with ATLAS in the single lepton channel

A measurement of the production cross-section for top quark pairs (t[bar over t]) in pp collisions at √s = 7 TeV is presented using data recorded with the ATLAS detector at the Large Hadron Collider. Events are selected in the single lepton topology by requiring an electron or muon, large missing transverse momentum and at least three jets. With a data sample of 35 pb[superscript −1], two different multivariate methods, one of which uses b-quark jet identification while the other does not, use kinematic variables to obtain cross-section measurements of σ[subscript t bar over t] = 187 ± 11 (stat.) [+18 over −17] (syst.) ± 6 (lumi.) pb and σ[subscript t bar over t] = 173 ± 17 (stat.) [+18 ove…

Search for the Xb and other hidden-beauty states in the π+π−ϒ(1S) channel at ATLAS

This Letter presents a search for a hidden-beauty counterpart of the X(3872) in the mass ranges 10.05--10.31 GeV and 10.40--11.00 GeV, in the channel Xb→π+π−Υ(1S)(→μ+μ−), using 16.2 fb−1 of s√=8 TeV pp collision data collected by the ATLAS detector at the LHC. No evidence for new narrow states is found, and upper limits are set on the product of the Xb cross section and branching fraction, relative to those of the Υ(2S), at the 95% confidence level using the CLS approach. These limits range from 0.8% to 4.0%, depending on mass. For masses above 10.1 GeV, the expected upper limits from this analysis are the most restrictive to date. Searches for production of the Υ(13DJ), Υ(10860), and Υ(110…

A search for flavour changing neutral currents in top-quark decays in pp collision data collected with the ATLAS detector at root s=7 TeV

A search for flavour changing neutral current (FCNC) processes in top-quark decays by the ATLAS Collaboration is presented. Data collected from pp collisions at the LHC at a centre-of-mass energy of √s = 7 TeV during 2011, corresponding to an integrated luminosity of 2.1 fb[superscript −1], were used. A search was performed for top-quark pair-production events, with one top quark decaying through the t → Zq FCNC (q = u, c) channel, and the other through the Standard Model dominant mode t → W b. Only the decays of the Z boson to charged leptons and leptonic W -boson decays were considered as signal. Consequently, the final-state topology is characterised by the presence of three isolated cha…

A measurement of the inclusive b → sγ branching ratio

The flavour changing neutral current decay b --&gt; s gamma has been detected in hadronic Z decays collected by ALEPH at LEP. The signal is isolated in lifetime-tagged b (b) over bar events by the presence of a hard photon associated with a system of high momentum and high rapidity hadrons. The background processes are normalised from the data themselves. The inclusive branching ratio is measured to be (3.11 +/- 0.80(stat) +/- 0.72(syst)) x 10(-4), consistent with the Standard Model expectation via penguin processes. (C) 1998 Published by Elsevier Science B.V. All rights reserved. The flavour changing neutral current decay b → sγ has been detected in hadronic Z decays collected by ALEPH at …

Study of the CP asymmetry of B0 -> J/psi K0S decays in ALEPH

The decay B0 -> J/psi K0_S is reconstructed with J/psi -> e+ e- or mu+ mu- and K0_S -> pi+ pi-. From the full ALEPH dataset at LEP1 of about 4 million hadronic Z decays, 23 candidates are selected with an estimated purity of 71%. They are used to measure the CP asymmetry of this decay, given by sin 2beta in the Standard Model, with the result sin 2beta = 0.84 +0.82-1.04 +-0.16. This is combined with existing measurements from other experiments, and increases the confidence level that CP violation has been observed in this channel to 98%.

Search for a fermiophobic Higgs boson in the diphoton decay channel with the ATLAS detector

[Excerpt] A search for a fermiophobic Higgs boson using diphoton events produced in proton-proton collisions at a centre-of-mass energy of s√=7 TeV is performed using data corresponding to an integrated luminosity of 4.9 fb−1 collected by the ATLAS experiment at the Large Hadron Collider. A specific benchmark model is considered where all the fermion couplings to the Higgs boson are set to zero and the bosonic couplings are kept at the Standard Model values (fermiophobic Higgs model). The largest excess with respect to the background-only hypothesis is found at 125.5 GeV, with a local significance of 2.9 standard deviations, which reduces to 1.6 standard deviations when taking into account …

Search for the Bc meson in hadronic Z decays

A search for the B-c meson decaying into the channels J/psi pi(+) and J/psi l(+)nu(l) (l = e or mu) is performed in a sample of 3.9 million hadronic Z decays collected by the ALEPH detector. This search results in the observation of 0 and 2 candidates in each of these channels, respectively, while 0.44 and 0.81 background events are expected. The following 90% confidence level upper limits are derived: Br(Z --> BcX)/Br(Z --> q (q) over bar BR(B-c(+) --> J/psi pi(+)) BcX)/Br(Z-->q (q) over bar)Br(B-c(+) --> J/psi l(+)nu) J/psi(e(+)e(-))mu(+)nu(mu) candidate with very low background probability, found in an independent analysis, is also described in detail. (C) 1997 Published by Elsevier Scie…

Measurement of exclusive γγ→ℓ+ℓ− production in proton–proton collisions at s=7 TeV with the ATLAS detector

This Letter reports a measurement of the exclusive gamma gamma -> l(+)l(-) (l = e, mu) cross-section in proton-proton collisions at a centre-of-mass energy of 7 TeV by the ATLAS experiment at the LHC, based on an integrated luminosity of 4.6 fb(-1). For the electron or muon pairs satisfying exclusive selection criteria, a fit to the dilepton acoplanarity distribution is used to extract the fiducial cross-sections. The cross-section in the electron channel is determined to be sigma(excl)(gamma gamma -> e+e-) = 0.428 +/- 0.035 (stat.) +/- 0.018 (syst.) pbfor a phase-space region with invariant mass of the electron pairs greater than 24GeV, in which both electrons have transverse momentum p(T)…

Probing the Quantum Interference between Singly and Doubly Resonant Top-Quark Production in pp Collisions at s=13  TeV with the ATLAS Detector

This Letter presents a normalized differential cross-section measurement in a fiducial phase-space region where interference effects between top-quark pair production and associated production of a single top quark with a W boson and a b-quark are significant. Events with exactly two leptons (ee, μμ, or eμ) and two b-tagged jets that satisfy a multiparticle invariant mass requirement are selected from 36.1  fb^{-1} of proton-proton collision data taken at sqrt[s]=13  TeV with the ATLAS detector at the LHC in 2015 and 2016. The results are compared with predictions from simulations using various strategies for the interference. The standard prescriptions for interference modeling are signifi…

Measurement of theW+W−Cross Section ins=7  TeVppCollisions with ATLAS

This Letter presents a measurement of the W+W- production cross section in root s = 7 TeV pp collisions by the ATLAS experiment, using 34 pb(-1) of integrated luminosity produced by the Large Hadron Collider at CERN. Selecting events with two isolated leptons, each either an electron or a muon, 8 candidate events are observed with an expected background of 1.7 +/- 0.6 events. The measured cross section is 41(-16)(+20)(stat) +/- 5(syst) +/- 1(lumi) pb, which is consistent with the standard model prediction of 44 +/- 3 pb calculated at next-to-leading order in QCD.

Study of jets produced in association with aWboson inppcollisions ats=7  TeVwith the ATLAS detector

We report a study of final states containing a W boson and hadronic jets, produced in proton-proton collisions at a center-of-mass energy of 7 TeV. The data were collected with the ATLAS detector at the CERN LHC and comprise the full 2010 data sample of 36 pb^-1. Cross sections are determined using both the electron and muon decay modes of the W boson and are presented as a function of inclusive jet multiplicity, N_jet, for up to five jets. At each multiplicity, cross sections are presented as a function of jet transverse momentum, the scalar sum of the transverse momenta of the charged lepton, missing transverse momentum, and all jets, the invariant mass spectra of jets, and the rapidity d…

Measurement of the W mass in e(+)e(-) collisions at production threshold

In June 1996, the LEP centre-of-mass energy was raised to 161 GeV. Pair production of W bosons in e(+)e(-) collisions was observed for the first time by the LEP experiments. An integrated luminosity of 11 pb(-1) was recorded in the ALEPH detector, in which WW candidate events were observed. In 6 events both Ws decay leptonically. In 16 events, one W decays leptonically, the other into hadrons. In the channel where both Ws decay into hadrons, a signal was separated from the large background by means of several multi-variate analyses. The W pair cross-section is measured to be sigma(ww) = 4.23 +/- 0.73(stat.) +/- 0.19(syst.) pb. From this cross-section, the W mass is derived within the framew…

The ATLAS Data Acquisition and High Level Trigger system

Journal of Instrumentation 11(06), P06008 (2016). doi:10.1088/1748-0221/11/06/P06008

Measurement of the cross-section for b-jets produced in association with a Z boson at s=7 TeV with the ATLAS detector

A measurement is presented of the inclusive cross-section for b-jet production in association with a Z boson in pp collisions at a centre-of-mass energy of root s = 7 TeV. The analysis uses the data sample collected by the ATLAS experiment in 2010, corresponding to an integrated luminosity of approximately 36 pb(-1). The event selection requires a Z boson decaying into high P-T electrons or muons, and at least one b-jet, identified by its displaced vertex, with transverse momentum p(T) > 25 GeV and rapidity vertical bar y vertical bar < 2.1. After subtraction of background processes, the yield is extracted from the vertex mass distribution of the candidate b-jets. The ratio of this cross-se…

Search for top squarks decaying to tau sleptons in pp collisions at s=13  TeV with the ATLAS detector

A search for direct pair production of top squarks in final states with two tau leptons, b-jets, and missing transverse momentum is presented. The analysis is based on proton-proton collision data ...

Observation of electroweak W±Z boson pair production in association with two jets in pp collisions at s=13 TeV with the ATLAS detector

An observation of electroweak W±Z production in association with two jets in proton–proton collisions is presented. The data collected by the ATLAS detector at the Large Hadron Collider in 2015 and 2016 at a centre-of-mass energy of s=13 TeV are used, corresponding to an integrated luminosity of 36.1fb−1 . Events containing three identified leptons, either electrons or muons, and two jets are selected. The electroweak production of W±Z bosons in association with two jets is measured with an observed significance of 5.3 standard deviations. A fiducial cross-section for electroweak production including interference effects and for a single leptonic decay mode is measured to be σWZjj−EW=0.57−0…

Search for contact interactions in the reactionse + e −→l + l − ande + e −→γγ

Contact interactions are searched for using the differential cross sections for the reactions e + e -→ e + e -, e + e -→ µ + µ -, e + e -→ τ + τ - and e + e -→γγ measured at 12 energies around the Z peak and corresponding to about 20 pb-1 of cumulated luminosity. Four-fermion contact term models assuming various chiralities of lepton currents are fitted to the lepton data and lower limits on the energy scale Λ of such terms are set at 95% c.l. The limits vary in the range 0.9 4.7 TeV, depending on the model and on the lepton flavour. The eeγγ contact terms are searched for assuming various chiralities. Limits on the energy scale Λ between 79 and 130 GeV are extracted from the data. The resu…

Search for Dark Matter in Events with a Hadronically DecayingWorZBoson and Missing Transverse Momentum inppCollisions ats=8  TeVwith the ATLAS Detector

A search is presented for dark matter pair production in association with a W or Z boson in pp collisions representing 20.3 fb(-1) of integrated luminosity at root s = 8 TeV using data recorded with the ATLAS detector at the Large Hadron Collider. Events with a hadronic jet with the jet mass consistent with a W or Z boson, and with large missing transverse momentum are analyzed. The data are consistent with the standard model expectations. Limits are set on the mass scale in effective field theories that describe the interaction of dark matter and standard model particles, and on the cross section of Higgs production and decay to invisible particles. In addition, cross section limits on the…

Search for dark matter in association with a Higgs boson decaying to two photons at s=13  TeV with the ATLAS detector

A search for dark matter in association with a Higgs boson decaying to two photons is presented. This study is based on data collected with the ATLAS detector, corresponding to an integrated lumino ...

Measurement of the transverse momentum distribution of Z/γ⁎ bosons in proton–proton collisions at s=7 TeV with the ATLAS detector

A measurement of the Z/gamma* transverse momentum (p(T)(Z)) distribution in proton-proton collisions at root s = 7 TeV is presented using Z/gamma* -> e(+)e(-) and Z/gamma* -> mu(+)mu(-) decay ...

Transverse momentum correlations in hadronic Z decays

Using data obtained with the ALEPH detector at the Z resonance, a measure based on transverse momentum is shown to exhibit a correlation between the two halves of a hadronic event which cannot be explained by energy-momentum conservation, flavour conservation, the imposition of an event axis or imperfect event reconstruction. Two possible interpretations based on existing Monte Carlo models are examined: a) ARIADNE, with the correlation forming early in the parton shower and with the transition from partons to hadrons playing only a minor part; b) JETSET, with the correlation forming at the fragmentation stage. A correlation technique based on a jet cluster analysis is used to make a compar…

The ATLAS Simulation Infrastructure

52 páginas, 10 figuras, 18 tablas.-- This article is distributed under the terms of the Creative Commons Attribution Noncommercial License.-- et al. (The ATLAS Collaboration).

Jet mass and substructure of inclusive jets in $ \sqrt {s} = 7\;{\text{TeV}} $ pp collisions with the ATLAS experiment

Recent studies have highlighted the potential of jet substructure techniques to identify the hadronic decays of boosted heavy particles. These studies all rely upon the assumption that the internal substructure of jets generated by QCD radiation is well understood. In this article, this assumption is tested on an inclusive sample of jets recorded with the ATLAS detector in 2010, which corresponds to 35 pb-1 of pp collisions delivered by the LHC at √s = 7TeV. In a subsample of events with single pp collisions, measurements corrected for detector efficiency and resolution are presented with full systematic uncertainties. Jet invariant mass, kt splitting scales and N-subjettiness variables are…

Search for flavor-changing neutral currents in top quark decays t→Hc and t→Hu in multilepton final states in proton-proton collisions at s=13  TeV with the ATLAS detector

Flavor-changing neutral currents are not present in the Standard Model at tree level and are suppressed in loop processes by the unitarity of the Cabibbo-Kobayashi-Maskawa matrix; the corresponding ...

Measurements of the pseudorapidity dependence of the total transverse energy in proton-proton collisions at sqrt(s) = 7 TeV with ATLAS

This paper describes measurements of the sum of the transverse energy of particles as a function of particle pseudorapidity, η, in proton-proton collisions at a centre-of-mass energy, √s = 7 TeV using the ATLAS detector at the Large Hadron Collider. The measurements are performed in the region |η| < 4.8 for two event classes: those requiring the presence of particles with a low transverse momentum and those requiring particles with a significant transverse momentum. In the second dataset measurements are made in the region transverse to the hard scatter. The distributions are compared to the predictions of various Monte Carlo event generators, which generally tend to underestimate the amoun…

Scalar quark searches in $e^+ e^-$ collisions at $\sqrt{s}$ = 181-184 GeV

Searches for scalar top, scalar bottom and degenerate scalar quarks have been performed with data collected with the ALEPH detector at LEP. The data sample consists of 57 pb^-1 taken at sqrt{s} = 181-184 GeV. No evidence for scalar top, scalar bottom or degenerate scalar quarks was found in the channels tilde{t} --&gt; c chi, tilde{t} --&gt; b l snu, tilde{b} --&gt; b chi, and tilde{q} --&gt; q chi. From the channel tilde{t} --&gt; c chi a limit of 74 GeV/c^2 has been set on the scalar top quark mass, independent of the mixing angle. This limit assumes a mass difference between the stop and the chi in the range 10-40 GeV/c^2. From the channel tilde{t} --&gt; b l snu the mixing-angle-indepen…

Search for supersymmetry in final states with jets, missing transverse momentum and one isolated lepton ins=7  TeVpp collisions using1  fb−1of ATLAS data

We present an update of a search for supersymmetry in final states containing jets, missing transverse momentum, and one isolated electron or muon, using 1.04 fb(-1) of proton-proton collision data at root s =7 TeV recorded by the ATLAS experiment at the LHC in the first half of 2011. The analysis is carried out in four distinct signal regions with either three or four jets and variations on the (missing) transverse momentum cuts, resulting in optimized limits for various supersymmetry models. No excess above the standard model background expectation is observed. Limits are set on the visible cross section of new physics within the kinematic requirements of the search. The results are inter…

Search for a Standard Model Higgs Boson in theH→ZZ→ℓ+ℓ−νν¯Decay Channel with the ATLAS Detector

A search for a heavy standard model Higgs boson decaying via H -> ZZ -> l(+)l(-)v (v) over bar, where l = e, mu, is presented. It is based on proton-proton collision data at root s = 7 TeV, collected by the ATLAS experiment at the LHC in the first half of 2011 and corresponding to an integrated luminosity of 1.04 fb(-1). The data are compared to the expected standard model backgrounds. The data and the background expectations are found to be in agreement and upper limits are placed on the Higgs boson production cross section over the entire mass window considered; in particular, the production of a standard model Higgs boson is excluded in the region 340 < m(H) < 450 GeV at the 95% confiden…

A study of the material in the ATLAS inner detector using secondary hadronic interactions

The ATLAS inner detector is used to reconstruct secondary vertices due to hadronic interactions of primary collision products, so probing the location and amount of material in the inner region of ATLAS. Data collected in 7 TeV pp collisions at the LHC, with a minimum bias trigger, are used for comparisons with simulated events. The reconstructed secondary vertices have spatial resolutions ranging from ~ 200μm to 1 mm. The overall material description in the simulation is validated to within an experimental uncertainty of about 7%. This will lead to a better understanding of the reconstruction of various objects such as tracks, leptons, jets, and missing transverse momentum.

Measurement of the cross section for top-quark pair production in pp collisions at √s = 7TeV with the ATLAS detector using final states with two high-p(T) leptons

A measurement is reported of the production cross section of top-quark pairs (tt¯) in proton-proton collisions at a center-of-mass energy of 7 TeV recorded with the ATLAS detector at the LHC. Candidate events have a signature consistent with containing two isolated leptons, large missing transverse momentum, and at least two jets. Using a data sample corresponding to an integrated luminosity of 0.70 fb−1, a tt¯ production cross section σtt¯=176±5(stat.)+14−11(syst.)±8(lum.) pb is measured for an assumed top-quark mass of mt = 172.5 GeV. This measurement is in good agreement with Standard Model predictions.

Evidence for the associated production of a W boson and a top quark in ATLAS at √s = 7 TeV

This Letter presents evidence for the associated production of a W boson and a top quark using 2.05 fb[superscript −1] of pp collision data at √s = 7 TeV accumulated with the ATLAS detector at the LHC. The analysis is based on the selection of the dileptonic final states with events featuring two isolated leptons, electron or muon, with significant transverse missing momentum and at least one jet. An approach based on boosted decision trees has been developed to improve the discrimination of single top-quark Wt events from background. A template fit to the final classifier distributions is performed to determine the cross-section. The result is incompatible with the background-only hypothes…

Measurements of Higgs boson production and couplings in diboson final states with the ATLAS detector at the LHC

We acknowledge the support of ANPCyT, Argentina; YerPhI, Armenia; ARC, Australia; BMWF and FWF, Austria; ANAS, Azerbaijan; SSTC, Belarus; CNPq and FAPESP, Brazil; NSERC, NRC and CFI, Canada; CERN; CONICYT, Chile; CAS, MOST and NSFC, China; COLCIENCIAS, Colombia; MSMT CR, MPO CR and VSC CR, Czech Republic; DNRF, DNSRC and Lundbeck Foundation, Denmark; EPLANET, ERC and NSRF, European Union; IN2P3-CNRS, CEA-DSM/IRFU, France; GNSF, Georgia; BMBF, DFG, HGF, MPG and AvH Foundation, Germany; GSRT and NSRF, Greece; ISF, MINERVA, GIF, DIP and Benoziyo Center, Israel; INFN, Italy; MEXT and JSPS, Japan; CNRST, Morocco; FOM and NWO, Netherlands; BRF and RCN, Norway; MNiSW, Poland; GRICES and FCT, Portu…

Search for charginos and neutralinos with R-parity violation at =130 136

Searches for charginos and neutralinos produced in e+e− collisions at centre-of-mass energies of 130 and 136 GeV have been performed under the assumptions that R-parity is not conserved, that the dominant R-parity violating coupling involves only leptonic fields, and that the lifetime of the lightest supersymmetric particle can be neglected. In the 5.7 pb−1 data sample collected by ALEPH, no candidate events were found. As a result, chargino and neutralino masses and couplings are constrained and the domains previously excluded at LEP1 are extended.

Measurement of the b → τ-ν̄τX branching ratio

The definitions of “anthropology” found in various dictionaries cover a whole range of terms and in this section we provide an overview of all its connotations. In this way a variety of reflections about the essence of man become possible, for instance as : summit of creation; source of his own values; specific biological reality; intelligence (but what is this, really?); knowing subject or object of knowledge; social being and product of a culture. Following these lines of thought one realises that all these preoccupations have already been taken up, or at least touched upon, by communication theory.

Search for new physics in the dijet mass distribution using 1 fb−1 of pp collision data at s=7 TeV collected by the ATLAS detector

Invariant mass distributions of jet pairs (dijets) produced in LHC proton-proton collisions at a centre-of-mass energy root s = 7 TeV have been studied using a data set corresponding to an integrat ...

Tau leptonic branching ratios

A sample of 62249 tau-pair events is selected from data taken with the ALEPH detector in 1991, 1992 and 1993. The measurement of the branching fractions for tau decays into electrons and muons is presented with emphasis on the study of systematic effects from selection, particle identification and decay classification. The results obtained are: B-e=17.79+/-0.12(stat)+/-0.06(syst)(%) and B-mu=17.31+/-0.11(stat)+/-0.05(syst)(%). Combined with the most recent ALEPH determination of the tau lifetime, these results provide a relative measurement of the leptonic couplings in the weak charged current for transverse W bosons: g(mu)/g(e)=1.0002+/-0.0051 and g(tau)/g(mu)=0.9943+/-0.0065. RI ANTONELLI…

Search fortbResonances in Proton-Proton Collisions ats=7  TeVwith the ATLAS Detector

This Letter presents a search for tb resonances in 1.04 fb(-1) of LHC proton-proton collision data collected by the ATLAS detector at a center-of-mass energy of 7 TeV. Events with a lepton, missing transverse momentum, and two jets are selected and the invariant mass of the corresponding final state is reconstructed. The search exploits the shape of the tb invariant mass distribution compared to the expected standard model backgrounds. The model of a right-handed W(R)' with standard model-like couplings is chosen as the benchmark model for this search. No statistically significant excess of events is observed in the data, and upper limits on the cross section times the branching ratio of W(…

Measurement of the cross section for the production of a W boson in association with b-jets in pp collisions at s=7 TeV with the ATLAS detector

A measurement is presented of the cross section for the production of a W boson with one or two jets, of which at least one must be a b-jet, in pp collisions at root s = 7 TeV. Production via top d ...

Determination of sin2 θeff w using jet charge measurements in hadronic Z decays

The electroweak mixing angle is determined with high precision from measurements of the mean difference between forward and backward hemisphere charges in hadronic decays of the Z. A data sample of 2.5 million hadronic Z decays recorded over the period 1990 to 1994 in the ALEPH detector at LEP is used. The mean charge separation between event hemispheres containing the original quark and antiquark is measured for bb̄ and cc̄ events in subsamples selected by their long lifetimes or using fast D*'s. The corresponding average charge separation for light quarks is measured in an inclusive sample from the anticorrelation between charges of opposite hemispheres and agrees with predictions of hadr…

Search for a multi-Higgs-boson cascade inW+W−bb¯events with the ATLAS detector inppcollisions ats=8  TeV

A search is presented for new particles in an extension to the Standard Model that includes a heavy Higgs boson (H-0), an intermediate charged Higgs-boson pair (H-+/-), and a light Higgs boson (h(0)). The analysis searches for events involving the production of a single heavy neutral Higgs boson which decays to the charged Higgs boson and a W boson, where the charged Higgs boson subsequently decays into a W boson and the lightest neutral Higgs boson decaying to a bottom-antibottom-quark pair. Such a cascade results in a W-boson pair and a bottom-antibottom-quark pair in the final state. Events with exactly one lepton, missing transverse momentum, and at least four jets are selected from a d…

Search for high-mass states with one lepton plus missing transverse momentum in proton–proton collisions at s=7 TeV with the ATLAS detector

The ATLAS detector is used to search for high-mass states, such as heavy charged gauge bosons (W', W*) decaying to a charged lepton (electron or muon) and a neutrino. Results are presented based on the analysis of pp collisions at a center-of-mass energy of 7 TeV corresponding to an integrated luminosity of 36 pb-1. No excess beyond standard model expectations is observed. A W' with sequential standard model couplings is excluded at 95% confidence level for masses below 1.49 TeV, and a W*(charged chiral boson) for masses below 1.47 TeV.

Searches for Higgs boson pair production in thehh→bbττ,γγWW*,γγbb,bbbbchannels with the ATLAS detector

Searches for both resonant and nonresonant Higgs boson pair production are performed in the hh -> bb tau tau, gamma gamma WW* final states using 20.3 fb(-1) of pp collision data at a center-of-m ...

Measurement of the top quark pair production cross section in pp collisions at s=7 TeV in dilepton final states with ATLAS

A measurement of the production cross section of top quark pairs (ttbar) in proton-proton collisions at a center-of-mass energy of 7 TeV recorded with the ATLAS detector at the Large Hadron Collider is reported. Candidate events are selected in the dilepton topology with large missing transverse energy and at least two jets. Using a data sample corresponding to an integrated luminosity of 35 pb^-1, a ttbar production cross section of 171 +/- 20(stat.) +/- 14(syst.) +8-6(lum.) pb is measured for an assumed top quark mass of 172.5 GeV. A second measurement requiring at least one jet identified as coming from a b quark yields a comparable result, demonstrating that the dilepton final states ar…

Constraints on off-shell Higgs boson production and the Higgs boson total width in ZZ → 4ℓ and ZZ → 2ℓ2ν final states with the ATLAS detector

A measurement of off-shell Higgs boson production in the and decay channels, where ℓ stands for either an electron or a muon, is performed using data from proton–proton collisions at a centre-of-mass energy of TeV. The data were collected by the ATLAS experiment in 2015 and 2016 at the Large Hadron Collider, and they correspond to an integrated luminosity of . An observed (expected) upper limit on the off-shell Higgs signal strength, defined as the event yield normalised to the Standard Model prediction, of 3.8 (3.4) is obtained at 95% confidence level (CL). Assuming the ratio of the Higgs boson couplings to the Standard Model predictions is independent of the momentum transfer of the Higgs…

Search for high mass photon pairs in (f= e, μ, τ, v, q) at LEP

Abstract The result of a search for high mass photon pairs from the processes e + e − → f f γγ (f = e, μ, τ, v and q) with the ALEPH detector is reported. The result for f = e , μ and τ is to be compared with the observation of 4 events by the L3 Collaboration with invariant masses, M γγ , of the two photons near 60 GeV. From a data sample approximately twice as large taken from 1990 to 1992, 6 events are found with M γγ distributed between 50 GeV and 72 GeV, while 4.9 events are expected from a QED calculation. There is no evidence for a mass peak; only one event ( μ + μ − γγ ) at M γγ = 59.4 ± 0.2 GeV is compatible with the L3 observation. In addition, for M γγ > 50 GeV, no event is found…

Search for the decay Bs0→μ+μ− with the ATLAS detector

A blind analysis searching for the decay B-s(0) -> mu(+)mu(-) has been performed using proton-proton collisions at a centre-of-mass energy of 7 TeV recorded with the ATLAS detector at the LHC. W ...

Search for the Standard Model Higgs boson in the decay channel H→ZZ(⁎)→4ℓ with the ATLAS detector

A search for the Standard Model Higgs boson in the decay channel H -> ZZ(()*()) l(+)l(-)l'l'(-), where l = e, mu, is presented. Proton-proton collision data at root s = 7 TeV recorded with the A ...

Study of muon-pair production at centre-of-mass energies from 20 to 136 GeV with the ALEPH detector

The total cross section and the forward-backward asymmetry for the process e(+)e --> mu(+)mu(-)(n gamma) are measured in the energy range 20-136 GeV by reconstructing the effective centre-of-mass energy after initial state radiation. The analysis is based on the data recorded with the ALEPH detector at LEP between 1990 and 1995, corresponding to a total integrated luminosity of 143.5 pb(-1). Two different approaches are used: in the first one an exclusive selection of events with hard initial state radiation in the energy range 20-88 GeV is directly compared with the Standard Model predictions showing good agreement. In the second one, all events are used to obtain a precise measurement of …

Studies of QCD in ${\rm e^+ e^-}\to $ hadrons at $E_{\rm cm} = 130$ and 136 GeV

Studies of QCD in $\mbox{e}^+\mbox{e}^- \rightarrow$ Hadrons at $E_{cm} = $} 130 and 136 GeV The ALEPH Collaboration An analysis of the properties of hadronic final states produced in electron-positron annihilation at centre-of-mass energies of 130 and 136 GeV is presented. The measurements are based on a data sample of 5.7 $\mbox{pb}^{-1}$ collected in November 1995 with the \Aleph detector at LEP. Inclusive charged particle distributions, jet rates and event-shape distributions are measured and the results are compared with the predictions of QCD-based models. From the measured distributions quantities are determined for which the dependence on the centre-of-mass energy can be predicted b…

Resonant structure and flavour tagging in the Bπ±system using fully reconstructed B decays

Abstract Starting from a sample of four million hadronic Z decays collected with the ALEPH detector at LEP, 404 charged and neutral B mesons are fully reconstructed and used to look for resonant structure in the Bπ system. An excess of events is observed above the expected background in the Bπ mass spectrum at a mass ≈5.7 GeV/c 2 , consistent with the production and decay to B (∗) π of the B ∗∗ states predicted by Heavy Quark Symmetry (HQS). In the framework of HQS, it is found that the mass of the B 2 ∗ state is (5739 + 8 −11 ( stat ) +6 −4 ( syst )) MeV/c 2 and the relative production rate of the B ∗∗ system is BR(b→B ∗∗ →B (∗) π)/BR(b→B u,d )=(31±9 (stat) +6 −5 (syst)) % . In the same sa…

Search for resonant top quark plus jet production intt¯+jetsevents with the ATLAS detector inppcollisions ats=7  TeV

This paper presents a search for a new heavy particle produced in association with a top or antitop quark. Two models in which the new heavy particle is a color singlet or a color triplet are considered, decaying, respectively, to (t)over-barq or tq, leading to a resonance within the t(t)over-bar + jets signature. The full 2011 ATLAS pp collision data set from the LHC (4.7 fb(-1)) is used to search for t(t)over-bar events produced in association with jets, in which one of the W bosons from the top quarks decays leptonically and the other decays hadronically. The data are consistent with the Standard Model expectation, and a new particle with mass below 430 Gev for both W' boson and color tr…

Characterisation and mitigation of beam-induced backgrounds observed in the ATLAS detector during the 2011 proton-proton run

This paper presents a summary of beam-induced backgrounds observed in the ATLAS detector and discusses methods to tag and remove background contaminated events in data. Triggerrate based monitoring of beam-related backgrounds is presented. The correlations of backgrounds with machine conditions, such as residual pressure in the beam-pipe, are discussed. Results from dedicated beam-background simulations are shown, and their qualitative agreement with data is evaluated. Data taken during the passage of unpaired, i.e. non-colliding, proton bunches is used to obtain background-enriched data samples. These are used to identify characteristic features of beam-induced backgrounds, which then are …

Measurement of Prompt Photon Production In Hadronic-z Decays

The production of isolated photons in hadronic Z decays is measured with the ALEPH detector at LEP using a sample of 450 000 hadronic events. The corrected rate is given for several values of the minimum invariant mass squared cut between the photon and the jets. This measurement of final state radiation from the quarks is compared with the predictions of parton shower models JETSET, ARIADNE and HERWIG as well as with the predictions of QCD matrix element calculations. RI Perrier, Frederic/A-5953-2011; ANTONELLI, ANTONELLA/C-6238-2011; Buttar, Craig/D-3706-2011; Stahl, Achim/E-8846-2011; Passalacqua, Luca/F-5127-2011; Murtas, Fabrizio/B-5729-2012; St.Denis, Richard/C-8997-2012; Forti, Franc…

Search for displaced vertices arising from decays of new heavy particles in 7 TeV pp collisions at ATLAS

We present the results of a search for new, heavy particles that decay at a significant distance from their production point into a final state containing charged hadrons in association with a high-momentum muon. The search is conducted in a pp-collision data sample with a center-of-mass energy of 7 TeV and an integrated luminosity of 33 pb[superscript −1] collected in 2010 by the ATLAS detector operating at the Large Hadron Collider. Production of such particles is expected in various scenarios of physics beyond the standard model. We observe no signal and place limits on the production cross-section of supersymmetric particles in an R-parity-violating scenario as a function of the neutral…

Measurement of the t-channel single top-quark production cross section in pp collisions at s=7 TeV with the ATLAS detector

We report a measurement of the cross section of single top-quark production in the t-channel using 1.04 fb -1 of pp collision data at s=7 TeV recorded with the ATLAS detector at the LHC. Selected e ...

Measurement of the azimuthal ordering of charged hadrons with the ATLAS detector

This paper presents a study of the possible ordering of charged hadrons in the azimuthal angle relative to the beam axis in high-energy proton-proton collisions at the Large Hadron Collider (LHC). A spectral analysis of correlations between longitudinal and transverse components of the momentum of the charged hadrons, driven by the search for phenomena related to the structure of the QCD field, is performed. Data were recorded with the ATLAS detector at center-of-mass energies of √s=900  GeV and √s=7  TeV. The correlations measured in a kinematic region dominated by low-pT particles are not well described by conventional models of hadron production. The measured spectra show features consis…

Measurement of the centrality dependence of the charged particle pseudorapidity distribution in lead–lead collisions at sNN=2.76 TeV with the ATLAS detector

The ATLAS experiment at the LHC has measured the centrality dependence of charged particle pseudorapidity distributions over vertical bar eta vertical bar < 2 in lead-lead collisions at a nucleo ...

Searches for neutral Higgs bosons in e+e− collisions at centre-of-mass energies from 192 to 202 GeV

Searches for neutral Higgs bosons are performed with the 237 pb-1 of data collected in 1999 by the ALEPH detector at LEP, for centre-of-mass energies between 191.6 and 201.6 GeV. These searches apply to Higgs bosons within the context of the Standard Model and its minimal supersymmetric extension (MSSM) as well as to invisibly decaying Higgs bosons. No evidence of a signal is seen. A lower limit on the mass of the Standard Model Higgs boson of 107.7 GeV/c2 at 95% confidence level is set. In the MSSM, lower limits of 91.2 and 91.6 GeV/c2 are derived for the masses of the neutral Higgs bosons h and A, respectively. For a Higgs boson decaying invisibly and produced with the Standard Model cros…

A layer correlation technique for pion energy calibration at the 2004 ATLAS Combined Beam Test

A new method for calibrating the hadron response of a segmented calorimeter is developed and successfully applied to beam test data. It is based on a principal component analysis of energy deposits in the calorimeter layers, exploiting longitudinal shower development information to improve the measured energy resolution. Corrections for invisible hadronic energy and energy lost in dead material in front of and between the calorimeters of the ATLAS experiment were calculated with simulated Geant4 Monte Carlo events and used to reconstruct the energy of pions impinging on the calorimeters during the 2004 Barrel Combined Beam Test at the CERN H8 area. For pion beams with energies between 20GeV…

A neural network clustering algorithm for the ATLAS silicon pixel detector

A novel technique to identify and split clusters created by multiple charged particles in the ATLAS pixel detector using a set of artificial neural networks is presented. Such merged clusters are a common feature of tracks originating from highly energetic objects, such as jets. Neural networks are trained using Monte Carlo samples produced with a detailed detector simulation. This technique replaces the former clustering approach based on a connected component analysis and charge interpolation. The performance of the neural network splitting technique is quantified using data from proton-proton collisions at the LHC collected by the ATLAS detector in 2011 and from Monte Carlo simulations. …

Search for Dark Matter Candidates and Large Extra Dimensions in Events with a Photon and Missing Transverse Momentum inppCollision Data ats=7  TeVwith the ATLAS Detector

A study of single W production in e+e− collisions at –183 GeV

Abstract Single W production is studied in the data recorded with the ALEPH detector at LEP at centre-of-mass energies between 161 and 183 GeV. The cross section is measured to be σW=0.41±0.17(stat.)±0.04(syst.) pb at 183 GeV, consistent with the Standard Model expectation. Limits on non-standard WWγ couplings are deduced as −1.6 γ (λ γ =0) and −1.6 γ (κ γ =1) at 95% C.L. A search for effectively invisible decays of the W boson in W pair production is performed, leading to an upper limit on the branching ratio of 1.3% ( Γ inv =27 MeV ) at 95% C.L.

Search for diphoton events with large missing transverse momentum in 1 fb−1 of 7 TeV proton–proton collision data with the ATLAS detector

A search for diphoton events with large missing transverse momentum has been performed using 1.07 fb(-1) of proton-proton collision data at root s = 7 TeV recorded with the ATLAS detector. No excess of events was observed above the Standard Model prediction and 95% Confidence Level (CL) upper limits are set on the production cross section for new physics. The limits depend on each model parameter space and vary as follows: sigma < (22-129) fb in the context of a generalised model of gauge-mediated supersymmetry breaking (GGM) with a bino-like lightest neutralino, sigma < (27-91) fb in the context of a minimal model of gauge-mediated supersymmetry breaking (SPS8), and sigma < (15-27) fb in t…

Four-fermion production in $e^+e^-$ collisions at centre-of-mass energies of 130 and 136 GeV

Four-fermion events have been selected in a data sample of 5.8 pb(-1) collected with the ALEPH detector at centre-of-mass energies of 130 and 136 GeV. The final states l(+)l(-), l(+)l(-)l(+)l(-), , and <l(+)l(-) have been examined Five events are observed in the data, in agreement with the Standard Model predictions of 6.67 +/- 0.38 events from four-fermion processes and 0.14(-0.05)(+0.19) from background processes. RI ANTONELLI, ANTONELLA/C-6238-2011; Passalacqua, Luca/F-5127-2011; Murtas, Fabrizio/B-5729-2012; Sanchez, Federico/F-5809-2012; Ferrante, Isidoro/F-1017-2012

Measurement of the isolated diphoton cross section inppcollisions ats=7  TeVwith the ATLAS detector

The ATLAS experiment has measured the production cross section of events with two isolated photons in the final state, in proton-proton collisions at √s=7  TeV. The full data set acquired in 2010 is used, corresponding to an integrated luminosity of 37  pb-1. The background, consisting of hadronic jets and isolated electrons, is estimated with fully data-driven techniques and subtracted. The differential cross sections, as functions of the di-photon mass (mγγ), total transverse momentum (pT,γγ), and azimuthal separation (Δϕγγ), are presented and compared to the predictions of next-to-leading-order QCD.

Search for new particles in two-jet final states in 7 TeV proton-proton collisions with the ATLAS detector at the LHC

19 páginas, 2 figuras, 1 tabla.-- et al.(ATLAS Collaboration).

A measurement of Rb using a lifetime-mass tag

ALEPH's published measurement of R-b = Gamma(Z --> b (b) over bar)/Gamma(Z --> hadrons) using a lifetime tag is updated using the full LEP 1 data sample. Considerable effort has been devoted to understanding systematic effects. Charm background is better controlled by combining the lifetime tag with a tag based on the b/c hadron mass difference. Furthermore, the algorithm used to reconstruct the event primary vertex is designed so as to reduce correlations between the two hemispheres of an event. The value of R-b is measured to be 0.2167 +/- 0.0011(stat) +/- 0.0013(syst). (C) 1997 Published by Elsevier Science B.V. RI ANTONELLI, ANTONELLA/C-6238-2011; Passalacqua, Luca/F-5127-2011; Murtas, …

Search for first generation scalar leptoquarks in pp collisions at s=7 TeV with the ATLAS detector

We report a search for first generation scalar leptoquarks using 1.03 fb(-1) of proton-proton collisions data produced by the Large Hadron Collider at root s = 7 TeV and recorded by the ATLAS experiment. Leptoquarks are sought via their decay into an electron or neutrino and a quark, producing events with two oppositely charged electrons and at least two jets, or events with an electron, missing transverse momentum and at least two jets. Control data samples are used to validate background predictions from Monte Carlo simulation. In the signal region, the observed event yields are consistent with the background expectations. We exclude at 95% confidence level the production of first generat…

Measurement of inclusive two-particle angular correlations in pp collisions with the ATLAS detector at the LHC

We present a measurement of two-particle angular correlations in proton- proton collisions at s√=900 GeV and 7 TeV. The collision events were collected during 2009 and 2010 with the ATLAS detector at the Large Hadron Collider using a single-arm minimum bias trigger. Correlations are measured for charged particles produced in the kinematic range of transverse momentum pT > 100 MeV and pseudorapidity |η| < 2.5. A complex structure in pseudorapidity and azimuth is observed at both collision energies. Results are compared to pythia 8 and herwig++ as well as to the AMBT2B, DW and Perugia 2011 tunes of pythia 6. The data are not satisfactorily described by any of these models.

Search for Pair Production of a Newb′Quark that Decays into aZBoson and a Bottom Quark with the ATLAS Detector

A search is reported for the pair production of a new quark b' with at least one b' decaying to a Z boson and a bottom quark. The data, corresponding to 2.0 fb(-1) of integrated luminosity, were co ...

Measurement of angular correlations in Drell–Yan lepton pairs to probe Z/γ⁎ boson transverse momentum at s=7 TeV with the ATLAS detector

A measurement of angular correlations in Drell-Yan lepton pairs via the phi(eta)* observable is presented. This variable probes the same physics as the Z/gamma* boson transverse momentum with a better experimental resolution. The Z/gamma* -> e(+)e(-) and Z/gamma* -> mu(+)mu(-) decays produced in proton-proton collisions at a centre-of-mass energy of root s = 7 TeV are used. The data were collected with the ATLAS detector at the LHC and correspond to an integrated luminosity of 4.6 fb(-1). Normalised differential cross sections as a function of phi(eta)* are measured separately for electron and muon decay channels. These channels are then combined for improved accuracy. The cross section is …

Measurement of the production cross section forZ/γ*in association with jets inppcollisions ats=7  TeVwith the ATLAS detector

Results are presented on the production of jets of particles in association with a Z/gamma* boson, in proton-proton collisions at root s = 7 TeV with the ATLAS detector. The analysis includes the full 2010 data set, collected with a low rate of multiple proton-proton collisions in the accelerator, corresponding to an integrated luminosity of 36 pb(-1). Inclusive jet cross sections in Z/gamma* events, with Z/gamma* decaying into electron or muon pairs, are measured for jets with transverse momentum p(T) > 30 GeV and jet rapidity vertical bar y vertical bar < 4.4. The measurements are compared to next-to-leading-order perturbative QCD calculations, and to predictions from different Monte Carl…

Measurement of the production cross section of an isolated photon associated with jets in proton-proton collisions ats=7  TeVwith the ATLAS detector

A measurement of the cross section for the production of an isolated photon in association with jets in proton-proton collisions at a center-of-mass energy root s = 7 TeV is presented. Photons are ...

Search for Resonant and Nonresonant Higgs Boson Pair Production in the bb¯τ+τ− Decay Channel in pp Collisions at s=13  TeV with the ATLAS Detector

A search for resonant and nonresonant pair production of Higgs bosons in the b (b) over bar tau(+)tau(-) final state is presented. The search uses 36.1 fb(-1) of pp collision data with root s = 13 ...

Further search for supersymmetry ats=7  TeVin final states with jets, missing transverse momentum, and isolated leptons with the ATLAS detector

This work presents a new inclusive search for supersymmetry (SUSY) by the ATLAS experiment at the LHC in proton-proton collisions at a center-of-mass energy root s = 7 TeV in final states with jets, missing transverse momentum and one or more isolated electrons and/or muons. The search is based on data from the full 2011 data-taking period, corresponding to an integrated luminosity of 4.7 fb(-1). Single-lepton and multilepton channels are treated together in one analysis. An increase in sensitivity is obtained by simultaneously fitting the number of events in statistically independent signal regions, and the shapes of distributions within those regions. A dedicated signal region is introduc…

Search for a Light Higgs Boson Decaying to Long-Lived Weakly Interacting Particles in Proton-Proton Collisions ats=7  TeVwith the ATLAS Detector

A search for the decay of a light Higgs boson (120-140 GeV) to a pair of weakly interacting, long-lived particles in 1.94 fb(-1) of proton-proton collisions at root s = 7 TeV recorded in 2011 by the ATLAS detector is presented. The search strategy requires that both long-lived particles decay inside the muon spectrometer. No excess of events is observed above the expected background and limits on the Higgs boson production times branching ratio to weakly interacting, long-lived particles are derived as a function of the particle proper decay length.

Drift Time Measurement in the ATLAS Liquid Argon Electromagnetic Calorimeter using Cosmic Muons

The ionization signals in the liquid argon of the ATLAS electromagnetic calorimeter are studied in detail using cosmic muons. In particular, the drift time of the ionization electrons is measured and used to assess the intrinsic uniformity of the calorimeter gaps and estimate its impact on the constant term of the energy resolution. The drift times of electrons in the cells of the second layer of the calorimeter are uniform at the level of 1.3% in the barrel and 2.8% in the endcaps. This leads to an estimated contribution to the constant term of (0.29-0.04+0.05)% in the barrel and (0.54-0.04+0.06)% in the endcaps. The same data are used to measure the drift velocity of ionization electrons …

Measurement of the W boson polarization in top quark decays with the ATLAS detector

This paper presents measurements of the polarization of W bosons in top quark decays, derived from t¯t events with missing transverse momentum, one charged lepton and at least four jets, or two charged leptons and at least two jets. Data from pp collisions at a centre-of-mass energy of 7 TeV were collected with the ATLAS experiment at the LHC and correspond to an integrated luminosity of 1.04 fb−1. The measured fractions of longitudinally, left- and right-handed polarization are F0 = 0.67 ± 0.07, FL = 0.32 ± 0.04 and FR = 0.01 ± 0.05, in agreement with the Standard Model predictions. As the polarization of the W bosons in top quark decays is sensitive to the Wtb vertex Lorentz structure and…

Measurement of the ratio using event shape variables

Abstract The branching fraction of Z → b b relative to all hadronic decays of the Z has been measured using event shape variables to preferentially select Z → b b events. The method chosen applies a combination of shape discriminators and the selection of high transverse momentum leptons to event hemispheres. From a sample of 440 000 hadronic Z decays collected with the ALEPH detector at LEP, the ration Γ b b Γ had = 0.228±0.005( stat. )±0.005( syst. ) is measured.

Inclusive production of the η and ω mesons in Z decays, and the muonic branching ratio of the ω

AbstractThe inclusive production of the η and ω(782) mesons is measured in the π+π−π0 decay mode in hadronic Z decays and compared to model predictions. The analysis is based on 4 million hadronic Z decays recorded by the ALEPH detector between 1991 and 1995. The η production rate for xp=pmeson/pbeam>0.10 is found to be 0.355±0.011stat±0.024sys per event, and the ω production rate for xp>0.05 is measured as 0.585±0.019stat±0.033sys per event. The branching ratio for ω→μ+μ− is investigated. A total of 18.1±5.9 events are observed, from which the muonic branching ratio is measured for the first time to be BR(ω→μ+μ−)=(9.0±2.9stat±1.1sys)×10−5.

Search for vectorlikeBquarks in events with one isolated lepton, missing transverse momentum, and jets ats=8  TeVwith the ATLAS detector

A search has been performed for pair production of heavy vectorlike down-type (B) quarks. The analysis explores the lepton-plus-jets final state, characterized by events with one isolated charged lepton (electron or muon), significant missing transverse momentum, and multiple jets. One or more jets are required to be tagged as arising from b quarks, and at least one pair of jets must be tagged as arising from the hadronic decay of an electroweak boson. The analysis uses the full data sample of pp collisions recorded in 2012 by the ATLAS detector at the LHC, operating at a center-of-mass energy of 8 TeV, corresponding to an integrated luminosity of 20.3 fb(-1). No significant excess of event…

Measurement of the jet fragmentation function and transverse profile in proton-proton collisions at a center-of-mass energy of 7 TeV with the ATLAS detector

The jet fragmentation function and transverse profile for jets with 25 GeV<pT jet<500 GeV and |ηjet|<1.2 produced in proton–proton collisions with a center-of-mass energy of 7 TeV are presented. The measurement is performed using data with an integrated luminosity of 36 pb−1. Jets are reconstructed and their momentum measured using calorimetric information. The momenta of the charged particle constituents are measured using the tracking system. The distributions corrected for detector effects are compared with various Monte Carlo event generators and generator tunes. Several of these choices show good agreement with the measured fragmentation function. None of these choices reproduce both t…

Search for heavy neutrinos and right-handed W bosons in events with two leptons and jets in pp collisions at √s=7 TeV with the ATLAS detector

This letter reports on a search for hypothetical heavy neutrinos, N, and right-handed gauge bosons, WR, in events with high transverse momentum objects which include two reconstructed leptons and at least one hadronic jet. The results were obtained from data corresponding to an integrated luminosity of 2.1 fb−1 collected in proton–proton collisions at √s=7 TeV with the ATLAS detector at the CERN Large Hadron Collider. No excess above the Standard Model background expectation is observed. Excluded mass regions for Majorana and Dirac neutrinos are presented using two approaches for interactions that violate lepton and lepton-flavor numbers. One approach uses an effective operator framework, t…

Search for Dark Matter in Events with Missing Transverse Momentum and a Higgs Boson Decaying to Two Photons inppCollisions ats=8  TeVwith the ATLAS Detector

Results of a search for new phenomena in events with large missing transverse momentum and a Higgs boson decaying to two photons are reported. Data from proton-proton collisions at a center-of-mass energy of 8 TeV and corresponding to an integrated luminosity of 20.3  fb−1 have been collected with the ATLAS detector at the LHC. The observed data are well described by the expected standard model backgrounds. Upper limits on the cross section of events with large missing transverse momentum and a Higgs boson candidate are also placed. Exclusion limits are presented for models of physics beyond the standard model featuring dark-matter candidates.

Searches for heavy long-lived sleptons and R-hadrons with the ATLAS detector in pp collisions at

A search for long-lived particles is performed using a data sample of 4.7 fb(-1) from proton-proton collisions at a centre-of-mass energy. root s = 7 TeV collected by the ATLAS detector at the LHC. No excess is observed above the estimated background and lower limits, at 95% confidence level, are set on the mass of the long-lived particles in different scenarios, based on their possible interactions in the inner detector, the calorimeters and the muon spectrometer. Long-lived staus in gauge-mediated SUSY-breaking models are excluded up to a mass of 300 GeV for tan beta = 5-20. Directly produced long-lived sleptons are excluded up to a mass of 278 GeV. R-hadrons, composites of gluino (stop, …

Searches for supersymmetry with the ATLAS detector using final states with two leptons and missing transverse momentum in s=7 TeV proton–proton collisions

Results of three searches are presented for the production of supersymmetric particles decaying into final states with missing transverse momentum and exactly two isolated leptons, e or mu. The analysis uses a data sample collected during the first half of 2011 that corresponds to a total integrated luminosity of 1 fb(-1) of root s = 7 TeV proton-proton collisions recorded with the ATLAS detector at the Large Hadron Collider. Opposite-sign and same-sign dilepton events are separately studied, with no deviations from the Standard Model expectation observed. Additionally, in opposite-sign events, a search is made for an excess of same-flavour over different-flavour lepton pairs. Effective pro…

Search for heavy resonances decaying to a photon and a hadronically decaying Z/W/H boson in pp collisions at s=13  TeV with the ATLAS detector

This Letter presents a search for the production of new heavy resonances decaying into a Higgs boson and a photon using proton-proton collision data at √ s = 13     TeV collected by the ATLAS detector at the LHC. The data correspond to an integrated luminosity of 139     fb − 1 . The analysis is performed by reconstructing hadronically decaying Higgs boson ( H → b ¯ b ) candidates as single large-radius jets. A novel algorithm using information about the jet constituents in the center-of-mass frame of the jet is implemented to identify the two b quarks in the single jet. No significant excess of events is observed above the expected background. Upper limits are set on the production cross-s…

Charm counting in b decays

??? The inclusive production of charmed particles in Z--> decays has been measured from the yield of D-0, D+, D-s(+) and Lambda(c)(+) decays in a sample of events with high b purity collected with the ALEPH detector from 1992 to 1995. From these measurements, adding the charmonia production rate and an estimate of the charmed strange baryon contribution, the average number of charm quarks per b decay is determined to be n(c)=1.230+/-0.036+/-0.038+/-0.053, where the uncertainties are due to statistics, systematic effects and branching ratios, respectively.

Measurement of the top quark pair cross section with ATLAS in pp collisions at s=7 TeV using final states with an electron or a muon and a hadronically decaying τ lepton

Measurement of the top quark pair cross section with ATLAS in pp collisions at root s=7 TeV using final states with an electron or a muon and a hadronically decaying tau lepton

Search for Higgs bosons produced via vector-boson fusion and decaying into bottom quark pairs in s=13  TeV pp collisions with the ATLAS detector

A search for the b (b) over bar decay of the Standard Model Higgs boson produced through vector-boson fusion is presented. Three mutually exclusive channels are considered: two all-hadronic channel ...

Measurement of isolated-photon pair production in pp collisions at root s=7 TeV with the ATLAS detector

The ATLAS experiment at the LHC has measured the production cross section of events with two isolated photons in the final state, in proton-proton collisions at √s = 7 TeV . The full data set collected in 2011, corresponding to an integrated luminosity of 4.9 fb[superscript −1], is used. The amount of background, from hadronic jets and isolated electrons, is estimated with data-driven techniques and subtracted. The total cross section, for two isolated photons with transverse energies above 25 GeV and 22 GeV respectively, in the acceptance of the electromagnetic calorimeter (|η|  0.4, is 44.0[+3.2 over −4.2] pb. The differential cross sections as a function of the di-photon invariant mass, …

Search for Production of Resonant States in the Photon-Jet Mass Distribution UsingppCollisions ats=7  TeVCollected by the ATLAS Detector

This Letter describes a model-independent search for the production of new resonant states in photon + jet events in 2.11 fb(-1) of proton-proton collisions at root s = 7 TeV. We compare the photon ...

Search for new phenomena in dijet events using 37  fb−1 of pp collision data collected at s=13  TeV with the ATLAS detector

Dijet events are studied in the proton-proton collision dataset recorded at root s = 13 TeV with the ATLAS detector at the Large Hadron Collider in 2015 and 2016, corresponding to integrated lumino ...

Measurement of the suppression and azimuthal anisotropy of muons from heavy-flavor decays in Pb+Pb collisions at sNN=2.76 TeV with the ATLAS detector

ATLAS measurements of the production of muons from heavy-flavor decays in root s(NN) = 2.76 TeV Pb+Pb collisions and root s = 2.76 TeV pp collisions at the LHC are presented. Integrated luminositie ...

Search for Supersymmetry Using Final States with One Lepton, Jets, and Missing Transverse Momentum with the ATLAS Detector ins=7  TeVppCollisions

This Letter presents the first search for supersymmetry in final states containing one isolated electron or muon, jets, and missing transverse momentum from sqrt{s} = 7 TeV proton-proton collisions at the LHC. The data were recorded by the ATLAS experiment during 2010 and correspond to a total integrated luminosity of 35 pb-1. No excess above the standard model background expectation is observed. Limits are set on the parameters of the minimal supergravity framework, extending previous limits. For A_0 = 0 GeV, tan beta = 3, mu > 0 and for equal squark and gluino masses, gluino masses below 700 GeV are excluded at 95% confidence level.

Search for new phenomena with the monojet and missing transverse momentum signature using the ATLAS detector in s=7TeV proton–proton collisions

A search for new phenomena in events featuring a high energy jet and large missing transverse momentum in proton-proton collisions at root s = 7 TeV is presented using a dataset corresponding to an integrated luminosity of 33 pb(-1) recorded with the ATLAS detector at the Large Hadron Collider. The number of observed events is consistent with the Standard Model prediction. This result is interpreted in terms of limits on a model of Large Extra Dimensions. (C) 2011 CERN. Published by Elsevier B.V. All rights reserved.

High-ET isolated-photon plus jets production in pp collisions at s=8 TeV with the ATLAS detector

The dynamics of isolated-photon plus one-, two- and three-jet production in pp collisions at a centre-of-mass energy of 8 TeV are studied with the ATLAS detector at the LHC using a data set with an ...

Measurement of Top Quark Polarization in Top-Antitop Events from Proton-Proton Collisions ats=7  TeVUsing the ATLAS Detector

This Letter presents measurements of the polarization of the top quark in top-antitop quark pair events, using 4: 7 fb(-1) of proton-proton collision data recorded with the ATLAS detector at the La ...

Properties of jets measured from tracks in proton-proton collisions at center-of-mass energys=7  TeVwith the ATLAS detector

Jets are identified and their properties studied in center-of-mass energy root s = 7 TeV proton-proton collisions at the Large Hadron Collider using charged particles measured by the ATLAS inner detector. Events are selected using a minimum bias trigger, allowing jets at very low transverse momentum to be observed and their characteristics in the transition to high-momentum fully perturbative jets to be studied. Jets are reconstructed using the anti-k(t) algorithm applied to charged particles with two radius parameter choices, 0.4 and 0.6. An inclusive charged jet transverse momentum cross section measurement from 4 GeV to 100 GeV is shown for four ranges in rapidity extending to 1.9 and co…

Observation of Spin Correlation intt¯Events fromppCollisions ats=7  TeVUsing the ATLAS Detector

A measurement of spin correlation in t (t) over bar production is reported using data collected with the ATLAS detector at the LHC, corresponding to an integrated luminosity of 2.1 fb(-1). Candidat ...

Search for the Higgs boson in the H→WW→ℓνjj decay channel at s=7 TeV with the ATLAS detector

A search for the Standard Model Higgs boson has been performed in the H→WW→lνjj channel using 4.7 fb^(−1) of pp collision data recorded at a centre-of-mass energy of √s = 7 TeV with the ATLAS detector at the Large Hadron Collider. Higgs boson candidates produced in association with zero, one or two jets are included in the analysis to maximize the acceptance for both gluon fusion and weak boson fusion Higgs boson production processes. No significant excess of events is observed over the expected background and limits on the Higgs boson production cross section are derived for a Higgs boson mass in the range 300 GeV<m_H<600 GeV. The best sensitivity is reached for m_H=400 GeV, where the obse…

Measurements of the top quark branching ratios into channels with leptons and quarks with the ATLAS detector

Measurements of the branching ratios of top quark decays into leptons and jets using events with t[bar over t] (top antitop) pairs are reported. Events were recorded with the ATLAS detector at the LHC in pp collisions at a center-of-mass energy of 7 TeV. The collected data sample corresponds to an integrated luminosity of 4.6  fb[superscript −1]. The measured top quark branching ratios agree with the Standard Model predictions within the measurement uncertainties of a few percent.

Search for third generation scalar leptoquarks in pp collisions at √s = 7 TeV with the ATLAS detector

A search for pair-produced third generation scalar leptoquarks is presented, using proton-proton collisions at √s = 7 TeV at the LHC. The data were recorded with the ATLAS detector and correspond to an integrated luminosity of 4.7 fb[superscript −1]. Each leptoquark is assumed to decay to a tau lepton and a b-quark with a branching fraction equal to 100%. No statistically significant excess above the Standard Model expectation is observed. Third generation leptoquarks are therefore excluded at 95% confidence level for masses less than 534 GeV.

Test of the flavour independence of αs

Abstract Using about 950000 hadronic events collected during 1991 and 1992 with the ALEPH detector, the ratios r b = α s b α s udsc and r uds = α s uds α s cb have been measured in order to test the flavour independence of the strong coupling constant α s . The analysis is based on event-shape variables using the full hadronic sample, two b -quark samples enriched by lepton tagging and lifetime tagging, and a light-quark sample enriched by lifetime antitagging. The combined results are r b = 1.002±0.023 and r uds = 0.971 ± 0.023.

Search for lepton flavour violation in the e mu continuum with the ATLAS detector in root s=7 TeV pp collisions at the LHC

This paper presents a search for the t-channel exchange of an R-parity violating scalar top quark ([~ over t] ) in the e[superscript ±]μ[superscript ∓] continuum using 2.1 fb[superscript −1] of data collected by the ATLAS detector in s√=7 TeV pp collisions at the Large Hadron Collider. Data are found to be consistent with the expectation from the Standard Model backgrounds. Limits on R-parity-violating couplings at 95 % C.L. are calculated as a function of the scalar top mass ( m[subscript bar over t]). The upper limits on the production cross section for pp→eμX, through the t-channel exchange of a scalar top quark, ranges from 170 fb for m[subscript ~ over t]=95 GeV to 30 fb for m[subscrip…

Search for contact interactions in dimuon events fromppcollisions ats=7  TeVwith the ATLAS detector

A search for contact interactions has been performed using dimuon events recorded with the ATLAS detector in proton-proton collisions at root s = 7 TeV. The data sample corresponds to an integrated ...

Search for the neutral Higgs bosons of the MSSM in e(+)e(-) collisions at root s from 130 to 172 GeV

The process e(+)e(-) --> hA is used to search for the Higgs bosons of the Minimal Supersymmetric Standard Model (MSSM), in the b (b) over bar b (b) over bar and tau(+)tau(-)b (b) over bar final states, The search is performed in the data collected by the ALEPH experiment at LEP, at centre-of-mass energies between 130 and 172 GeV and with a total luminosity of 27.2 pb(-1). No candidate events are found in either of the final states, in agreement with the expected background of 0.91 events from all Standard Model processes. Combined with searches for e(+)e(-) --> hZ, this results in a 95% C.L. lower limit on the masses of both h and A of 62.5 GeV/c(2), for tan beta > 1. (C) 1997 Elsevier Scie…

Charged-particle multiplicities in pp interactions measured with the ATLAS detector at the LHC

Measurements are presented from proton–proton collisions at centre-of-mass energies of \sqrt{s} = 0.9 , 2.36 and 7 TeV recorded with the ATLAS detector at the LHC. Events were collected using a single-arm minimum-bias trigger. The charged-particle multiplicity, its dependence on transverse momentum and pseudorapidity and the relationship between the mean transverse momentum and charged-particle multiplicity are measured. Measurements in different regions of phase space are shown, providing diffraction-reduced measurements as well as more inclusive ones. The observed distributions are corrected to well-defined phase-space regions, using model-independent corrections. The results are compared…

Search for direct stau production in events with two hadronic τ -leptons in s=13  TeV pp collisions with the ATLAS detector

A search for the direct production of the supersymmetric partners of τ -leptons (staus) in final states with two hadronically decaying τ -leptons is presented. The analysis uses a dataset of p p collisions corresponding to an integrated luminosity of 139     fb − 1 , recorded with the ATLAS detector at the Large Hadron Collider at a center-of-mass energy of 13 TeV. No significant deviation from the expected Standard Model background is observed. Limits are derived in scenarios of direct production of stau pairs with each stau decaying into the stable lightest neutralino and one τ -lepton in simplified models where the two stau mass eigenstates are degenerate. Stau masses from 120 GeV to 390…

Performance of the upgraded PreProcessor of the ATLAS Level-1 Calorimeter Trigger

The PreProcessor of the ATLAS Level-1 Calorimeter Trigger prepares the analogue trigger signals sent from the ATLAS calorimeters by digitising, synchronising, and calibrating them to reconstruct transverse energy deposits, which are then used in further processing to identify event features. During the first long shutdown of the LHC from 2013 to 2014, the central components of the PreProcessor, the Multichip Modules, were replaced by upgraded versions that feature modern ADC and FPGA technology to ensure optimal performance in the high pile-up environment of LHC Run 2. This paper describes the features of the newMultichip Modules along with the improvements to the signal processing achieved.

Measurement of the pseudorapidity and transverse momentum dependence of the elliptic flow of charged particles in lead–lead collisions at sNN=2.76 TeV with the ATLAS detector

This Letter describes the measurement of elliptic flow of charged particles in lead-lead collisions at root s(NN) = 2.76 TeV using the ATLAS detector at the Large Hadron Collider (LHC). The results ...

Readiness of the ATLAS Tile Calorimeter for LHC collisions

67 páginas.-- El PDF es la versión pre-print (arXiv:1007.5423v2).-- The ATLAS Collaboration.-- et al.

Measurement of the branching fraction for D0 → K-π+

The branching fraction for D-0 --> K(-)pi(+) is measured with the statistics collected by ALEPH from 1991 to 1994. The method is based on the comparison between the rate for the reconstructed D*+ --> (D) pi(+), D-0 --> K(-)pi(+) decay chain and the rate for inclusive soft pion production at low transverse momentum with respect to the nearest jet. The result is B(D-0 --> K(-)pi(+)) = (3.90 +/- 0.09 +/- 0.12)% (C) 1997 Published by Elsevier Science B.V. RI ANTONELLI, ANTONELLA/C-6238-2011; Passalacqua, Luca/F-5127-2011; Murtas, Fabrizio/B-5729-2012; St.Denis, Richard/C-8997-2012; Sanchez, Federico/F-5809-2012; Forti, Francesco/H-3035-2011; Ferrante, Isidoro/F-1017-2012

An experimental study of γγ → hadrons at LEP

An analysis of γγ interactions has been performed using untagged hadronic data obtained by the ALEPH detector at LEP. The data show at low transverse momentum (pt) are well reproduced by a model based on the vector meson dominance mechinism (VDM). At high pt thrust the presence of hard scattering processes is demonstrated. This component is well described in shape and normalization by a QCD calculation.

Search for a non-minimal Higgs boson produced in the reaction →

Abstract A data sample corresponding to 1.23 million hadronic Z decays collected by the ALEPH detector at LEP has been searched for signals of the production of a non-minimal CP-even Higgs boson h in the reaction e + e − → hZ ∗ . The h decay modes considered were: those of the minimal standard model Higgs boson, with modified branching ratios; decays into a pair of CP-odd Higgs bosons A; and decays into invisible final states. Only one event was found, a very acoplanar e+e− pair which could originate from the standard model background process e + e − → e + e − v v . Upper limits for the cross-section of the reaction e + e − → hZ ∗ have been derived as a function of mh, the mass of the Higgs…

Measurement of the W±Z production cross section and limits on anomalous triple gauge couplings in proton–proton collisions at s=7 TeV with the ATLAS detector

This Letter presents a measurement of W(+/-)Z production in 1.02 fb(-1) of pp collision data at root s = 7 TeV collected by the ATLAS experiment in 2011. Doubly leptonic decay events are selected w ...

Measurement of the inclusive jet cross-section in pp collisions at $\sqrt{s}=2.76\ \mbox{TeV}$ and comparison to the inclusive jet cross-section at $\sqrt{s} =7\ \mbox{TeV}$ using the ATLAS detector

The inclusive jet cross-section has been measured in proton-proton collisions at sqrt(s)=2.76 TeV in a dataset corresponding to an integrated luminosity of 0.20pb-1 collected with the ATLAS detector at the Large Hadron Collider in 2011. Jets are identified using the anti-kt algorithm with two radius parameters of 0.4 and 0.6. The inclusive jet double-differential cross-section is presented as a function of the jet transverse momentum pT and jet rapidity y, covering a range of 20 &lt;= pT &lt; 430 GeV and |y| &lt; 4.4. The ratio of the cross-section to the inclusive jet cross-section measurement at sqrt(s)=7 TeV, published by the ATLAS Collaboration, is calculated as a function of both trans…

Production of orbitally excited charm mesons in semileptonic B decays

A sample of 3.6 million hadronic Z decays recorded between 1991 and 1995 with the ALEPH detector at LEP is used to investigate semileptonic decays of B mesons into final states involving orbitally excited charm mesons. Topological vertex criteria are used to search for decays involving narrow D** states as well as wide D** resonances and non-resonant D(*)pi final states. The sum of the branching ratios for these processes is measured to be Br((B) over bar --> D pi l(-)(v) over bar) + Br((B) over bar --> D*pi l(-)(v) over bar) = (2.26 +/-t 0.29(stat) +/- 0.33(syst))%, which accounts for a significant fraction of the deficit between inclusive measurements and the sum of exclusive semileptonic…

Search for top and bottom squarks from gluino pair production in final states with missing transverse energy and at least three b-jets with the ATLAS detector

This letter reports the results of a search for top and bottom squarks from gluino pair production in 4.7 fb[superscript −1] of pp collisions at s√=7 TeV using the ATLAS detector at the LHC. The search is performed in events with large missing transverse momentum and at least three jets identified as originating from a b-quark. Exclusion limits are presented for a variety of gluino-mediated models with gluino masses up to 1 TeV excluded.

Search for same-sign top-quark production and fourth-generation down-type quarks in pp collisions at √s = 7 TeV with the ATLAS detector

A search is presented for same-sign top-quark production and down-type heavy quarks of charge −1/3 in events with two isolated leptons (e or μ) that have the same electric charge, at least two jets and large missing transverse momentum. The data are selected from pp collisions at √s=7TeV recorded by the ATLAS detector and correspond to an integrated luminosity of 1.04 fb−1. The observed data are consistent with expectations from Standard Model processes. Upper limits are set at 95 % confidence level on the cross section of new sources of same-sign top-quark pair production of 1.4-2.0 pb depending on the assumed mediator mass. Upper limits are also set on the pair-production cross-section fo…

Forward-backward correlations and charged-particle azimuthal distributions in $pp$ interactions using the ATLAS detector

Using inelastic proton-proton interactions at sqrt(s) = 900 GeV and 7 TeV, recorded by the ATLAS detector at the LHC, measurements have been made of the correlations between forward and backward charged-particle multiplicities and, for the first time, between forward and backward charged-particle summed transverse momentum. In addition, jet-like structure in the events is studied by means of azimuthal distributions of charged particles relative to the charged particle with highest transverse momentum in a selected kinematic region of the event. The results are compared with predictions from tunes of the PYTHIA and HERWIG++ Monte Carlo generators, which in most cases are found to provide a r…

A precise measurement of ΓZ→bb/ΓZ→hadrons

A measurement of the partial width ratio Γbb/Γhad using a method which tags the Z --> bb decays through the lif etime of the produced heavy hadrons is presented. This method relies on the tracking precision afforded by a double-sided silicon vertex detector. The tag algorithm makes a probabilistic interpretation of three-dimensional track impact parameters, using the data to measure the resolution. By tagging the two b hadrons separately, both Γbb/Γhad and the tag efficiency can be determined from the data. For a 26% efficiency of tagging a single b hadron within the vertex detector solid angle coverage, a purity of 96% is achieved. A value of Γbb/Γhad = 0.2192+/-0.0026(stat.)+/-0.0016(Γcc/…

Search for a right-handed gauge boson decaying into a high-momentum heavy neutrino and a charged lepton in pp collisions with the ATLAS detector at s=13 TeV

A search for a right-handed gauge boson WR, decaying into a boosted right-handed heavy neutrino NR, in the framework of Left-Right Symmetric Models is presented. It is based on data from proton–proton collisions with a centre-of-mass energy of 13 TeV collected by the ATLAS detector at the Large Hadron Collider during the years 2015, 2016 and 2017, corresponding to an integrated luminosity of 80 fb$^{−1}$. The search is performed separately for electrons and muons in the final state. A distinguishing feature of the search is the use of large-radius jets containing electrons. Selections based on the signal topology result in smaller background compared to the expected signal. No significant d…

Search for the Standard Model Higgs boson in e+e− collisions at =161, 170 172

The reaction e(+)e(-) --> HZ is used to search for the Standard Model Higgs boson, The data sample consists of integrated luminosities of 10.9 pb(-1), 1.1 pb(-1), and 9.5 pb(-1) collected by the ALEPH experiment at LEP during 1996, at centre-of-mass energies of 161, 170 and 172 GeV, respectively. No candidate events were found, in agreement with the expected background of 0.84 events from all Standard Model processes. This search results in a 95% C.L. lower limit on the Higgs boson mass of 69.4 GeV/c(2). When combined with earlier ALEPH searches performed at energies at and around the Z peak, this limit increases to 70.7 GeV/c(2). (C) 1997 Elsevier Science B.V.

Search for sleptons in e+e− collisions at centre-of-mass energies of 161 GeV and 172 GeV

The data recorded by the ALEPH experiment at LEP at centre-of-mass energies of 161 GeV and 172 GeV were analysed to search for sleptons, the supersymmetric partners of leptons. No evidence for the production of these particles was found. The number of candidates observed is consistent with the background expected from four-fermion processes and gammagamma-interactions. Improved mass limits at 95% C.L. are reported.

Search for neutral MSSM Higgs bosons decaying to τ+τ− pairs in proton–proton collisions at s=7 TeV with the ATLAS detector

A search for neutral Higgs bosons decaying to pairs of tau leptons with the ATLAS detector at the LHC is presented. The analysis is based on proton-proton collisions at a center-of-mass energy of 7 TeV, recorded in 2010 and corresponding to an integrated luminosity of 36 pb^-1. After signal selection, 276 events are observed in this data sample. The observed number of events is consistent with the total expected background of 269 +/- 36 events. Exclusion limits at the 95% confidence level are derived for the production cross section of a generic Higgs boson phi as a function of the Higgs boson mass and for A/H/h production in the Minimal Supersymmetric Standard Model (MSSM) as a function of…

Measurement of the inclusive isolated prompt photon cross section inppcollisions ats=7  TeVwith the ATLAS detector

A measurement of the cross section for the inclusive production of isolated prompt photons in pp collisions at a center-of-mass energy root s = 7 TeV is presented. The measurement covers the pseudorapidity ranges vertical bar eta(gamma)vertical bar < 1: 37 and 1: 52 <= vertical bar eta(gamma)vertical bar < 1: 81 in the transverse energy range 15 <= E-T(gamma) < 100 GeV. The results are based on an integrated luminosity of 880 nb(-1), collected with the ATLAS detector at the Large Hadron Collider. Photon candidates are identified by combining information from the calorimeters and from the inner tracker. Residual background in the selected sample is estimated from data based on the observed d…

Search for Supersymmetric Particles in e+e- Collisions at sqrt(s) up to 202GeV and Mass Limit for the Lightest Neutralino

Searches for pair production of squarks, sleptons, charginos, and neutralinos are performed with the data collected by the ALEPH detector at LEP at centre-of-mass energies from 188.6 to 201.6 GeV. No evidence for any such signals is observed in a total integrated luminosity of about 410pb-1. The negative results of the searches are translated into exclusion domains in the space of the relevant MSSM parameters, which improve significantly on the constraints set previously. Under the assumptions of gaugino and sfermion mass unification, these results allow a 95% C.L. lower limit of 37GeV/c2 to be set on the mass of the lightest neutralino for any tan beta and sfermion mass. Additional constra…

Worldwide comparison of ovarian cancer survival: Histological group and stage at diagnosis (CONCORD-2)

Abstract Objective Ovarian cancer comprises several histological groups with widely differing levels of survival. We aimed to explore international variation in survival for each group to help interpret international differences in survival from all ovarian cancers combined. We also examined differences in stage-specific survival. Methods The CONCORD programme is the largest population-based study of global trends in cancer survival, including data from 60 countries for 695,932 women (aged 15–99years) diagnosed with ovarian cancer during 1995–2009. We defined six histological groups: type I epithelial, type II epithelial, germ cell, sex cord-stromal, other specific non-epithelial and non-sp…

Measurement of W-pair production in e+e- collisions at 183 GeV

The production of W+W- pairs is analysed in a data sample collected by ALEPH at a mean centre-of-mass energy of 182.7 GeV, corresponding to an integrated luminosity of 57 pb-1. Cross sections are given for different topologies of W decays into leptons or hadrons. Under Standard Model assumptions for the W-pair production and decay, the W-pair cross section is measured to be 15.57+-0.62(stat.)+-0.29(syst.) pb. Using also the W-pair data samples collected by ALEPH at lower centre-of-mass energies, the decay branching ratio of the W boson into hadrons is measured to be B(W-&gt;hadrons)= 68.93+-1.21(stat.)+-0.51(syst.)%, allowing a determination of the CKM matrix element |Vcs|= 1.043 +- 0.058(s…

The longest homogeneous series of grape harvest dates, Beaune 1354–2018, and its significance for the understanding of past and present climate

Records of grape harvest dates (GHDs) are the oldest and the longest continuous phenological data in Europe. However, many available series, including the well-known (Dijon) Burgundy series, are error prone because scholars so far have uncritically drawn the data from 19th century publications instead of going back to the archives. The GHDs from the famous vine region of Beaune (Burgundy) were entirely drawn from the archives and critically cross-checked with narrative evidence. In order to reconstruct temperature, the series was calibrated against the long Paris temperature series comprising the 360 years from 1659 to 2018. The 664-year-long Beaune series from 1354 to 2018 is also signific…

Search for excited leptons in proton-proton collisions ats=7  TeVwith the ATLAS detector

The ATLAS detector is used to search for excited leptons in the electromagnetic radiative decay channel l* -> l gamma. Results are presented based on the analysis of pp collisions at a center-of ...

Search for supersymmetry in events with four or more leptons in s=13  TeV pp collisions with ATLAS

Results from a search for supersymmetry in events with four or more charged leptons (electrons, muons and taus) are presented. The analysis uses a data sample corresponding to 36.1 fb-1 of proton-proton collisions delivered by the Large Hadron Collider at s=13 TeV and recorded by the ATLAS detector. Four-lepton signal regions with up to two hadronically decaying taus are designed to target a range of supersymmetric scenarios that can be either enriched in or depleted of events involving the production and decay of a Z boson. Data yields are consistent with Standard Model expectations and results are used to set upper limits on the event yields from processes beyond the Standard Model. Exclu…

Inclusive π±, K± and(p,p¯) differential cross-sections at the Z resonance

Inclusive π±, K± and $$(p,\bar p)$$ differential cross-sections in hadronic decays of the Z have been measured as a function ofz=P hadron/P beam, the scaled momentum. The results are based on approximately 520 000 events measured by the ALEPH detector at LEP during 1992. Charged particles are identified by their rate of ionization energy loss in the ALEPH Time Projection Chamber. The position, ξ*, of the peak in the ln(1/z) distribution is determined, and the evolution of the peak position with centre-of-mass energy is compared with the prediction of QCD.

Search for direct slepton and gaugino production in final states with two leptons and missing transverse momentum with the ATLAS detector in pp collisions at

A search for the electroweak pair production of charged sleptons and weak gauginos decaying into final states with two leptons is performed using 4.7 fb(-1) of proton-proton collision data at root s = 7 TeV recorded with the ATLAS experiment at the Large Hadron Collider. No significant excesses are observed with respect to the prediction from Standard Model processes. In the scenario of direct slepton production, if the sleptons decay directly into the lightest neutralino, left-handed slepton masses between 85 and 195 GeV are excluded at 95% confidence level for a 20 GeV neutralino. Chargino masses between 110 and 340 GeV are excluded in the scenario of direct production of wino-like chargi…

Measurement of t ¯ t production with a veto on additional central jet activity in pp collisions at √ s = 7 TeV using the ATLAS detector

A measurement of the jet activity in t[bar over t] events produced in proton–proton collisions at a centre-of-mass energy of 7 TeV is presented, using 2.05 fb[superscript −1] of integrated luminosity collected by the ATLAS detector at the Large Hadron Collider. The t[bar over t] events are selected in the dilepton decay channel with two identified b-jets from the top quark decays. Events are vetoed if they contain an additional jet with transverse momentum above a threshold in a central rapidity interval. The fraction of events surviving the jet veto is presented as a function of this threshold for four different central rapidity interval definitions. An alternate measurement is also perfor…

Measurement of the and B− meson lifetimes

Abstract The lifetimes of the B 0 and B − mesons have been measured with the ALEPH detector at LEP. Semileptonic decays of B 0 and B − mesons were partially reconstructed by identifying events containing a lepton with an associated D ∗+ or D 0 meson. The proper time of the B meson was estimated from the measured decay length and the momentum and mass of the D -lepton system. A fit to the proper time of 77 D ∗+ l − and 77 D 0 l − candidates, combined with a constraint on the lifetime ratio ( τ − τ 0 ) arising from the relative rates of observed D ∗+ l − and D 0 l − events, yielded the following lifetimes: τ 0 =1.52 −0.18 +0.20 ( stat. ) −0.13 +0.07 ( syst. ) ps , τ − = 1.47 −0.19 +0.22 ( sta…

Charged-particle multiplicities in pp interactions at s=900 GeV measured with the ATLAS detector at the LHC

The first measurements from proton-proton collisions recorded with the ATLAS detector at the LHC are presented. Data were collected in December 2009 using a minimum-bias trigger during collisions at a centre-of-mass energy of 900 GeV. The charged-particle multiplicity, its dependence on transverse momentum and pseudorapidity, and the relationship between mean transverse momentum and charged-particle multiplicity are measured for events with at least one charged particle in the kinematic range vertical bar eta vertical bar 500 MeV. The measurements are compared to Monte Carlo models of proton-proton collisions and to results from other experiments at the same centre-of-mass energy. The charg…

Search for photonic signatures of gauge-mediated supersymmetry in 8TeV pp collisions with the ATLAS detector

A search is presented for photonic signatures motivated by generalized models of gauge-mediated supersymmetry breaking. This search makes use of 20.3  fb[superscript −1] of proton-proton collision data at √s = 8  TeV recorded by the ATLAS detector at the LHC, and explores models dominated by both strong and electroweak production of supersymmetric partner states. Four experimental signatures incorporating an isolated photon and significant missing transverse momentum are explored. These signatures include events with an additional photon, lepton, b-quark jet, or jet activity not associated with any specific underlying quark flavor. No significant excess of events is observed above the Stand…

Search for strong gravity signatures in same-sign dimuon final states using the ATLAS detector at the LHC

A search for microscopic black holes has been performed in a same-sign dimuon final state using 1.3 fb[superscript −1] of proton–proton collision data collected with the ATLAS detector at a centre of mass energy of 7 TeV at the CERN Large Hadron Collider. The data are found to be consistent with the expectation from the Standard Model and the results are used to derive exclusion contours in the context of a low scale gravity model.

Search for Gluinos in Events with Two Same-Sign Leptons, Jets, and Missing Transverse Momentum with the ATLAS Detector in Collisions at

A search is presented for gluinos decaying via the supersymmetric partner of the top quark using events with two same-sign leptons, jets, and missing transverse momentum. The analysis is performed ...

Search for the Standard Model Higgs boson in the H→WW(⋆)→ℓνℓν decay mode with 4.7 fb−1 of ATLAS data at s=7 TeV

A search for the Standard Model Higgs boson in the H -> WW(*()) -> lvlv (l = e.mu) decay mode is presented. The search is performed using proton-proton collision data corresponding to an inte ...

Underlying event characteristics and their dependence on jet size of charged-particle jet events inppcollisions at(s)=7  TeVwith the ATLAS detector

Distributions sensitive to the underlying event are studied in events containing one or more charged-particle jets produced in pp collisions at sqrt(s) = 7 TeV with the ATLAS detector at the Large Hadron Collider (LHC). These measurements reflect 800 inverse microbarns of data taken during 2010. Jets are reconstructed using the antikt algorithm with radius parameter R varying between 0.2 and 1.0. Distributions of the charged-particle multiplicity, the scalar sum of the transverse momentum of charged particles, and the average charged-particle pT are measured as functions of pT^JET in regions transverse to and opposite the leading jet for 4 GeV < pT^JET < 100 GeV. In addition, the R-dependen…

Measurement of the ϒ(1S) production cross-section in pp collisions at s=7 TeV in ATLAS

A measurement of the cross-section for ϒ ( 1 S ) → μ + μ − production in proton–proton collisions at centre of mass energy of 7 TeV is presented. The cross-section is measured as a function of the ϒ ( 1 S ) transverse momentum in two bins of rapidity, | y ϒ ( 1 S ) | 4 GeV and pseudorapidity | η μ | < 2.5 in order to reduce theoretical uncertainties on the acceptance, which depend on the poorly known polarisation. The results are based on an integrated luminosity of 1.13 pb−1, collected with the ATLAS detector at the Large Hadron Collider. The cross-section measurement is compared to theoretical predictions: it agrees to within a factor of two with a prediction based on the NRQCD model incl…

Search for a standard model Higgs boson in the H→ZZ→ℓ+ℓ−νν¯ decay channel using 4.7 fb−1 of s=7 TeV data with the ATLAS detector

A search for a Standard Model Higgs boson decaying via H -> ZZ -> l(+)l(-) nu(nu) over bar, where l represents electrons or muons, is presented. It is based on proton-proton collision data at ...

Determination of the Strange-Quark Density of the Proton from ATLAS Measurements of theW→ℓνandZ→ℓℓCross Sections

AQCD analysis is reported of ATLAS data on inclusive W-+/- and Z boson production in pp collisions at the LHC, jointly with ep deep-inelastic scattering data from HERA. The ATLAS data exhibit sensitivity to the light quark sea composition and magnitude at Bjorken x similar to 0:01. Specifically, the data support the hypothesis of a symmetric composition of the light quark sea at low x. The ratio of the strange-to-down sea quark distributions is determined to be 1:00(-0:28)(+0.25) at absolute four-momentum transfer squared Q(2) = 1: 9 GeV2 and x = 0: 023.

Search for Supersymmetry in Events with Three Leptons and Missing Transverse Momentum ins=7  TeVppCollisions with the ATLAS Detector

A search for the weak production of charginos and neutralinos decaying to a final state with three leptons (electrons or muons) and missing transverse momentum is presented. The analysis uses 2.06 fb(-1) of root s = 7 TeV proton-proton collision data delivered by the Large Hadron Collider and recorded with the ATLAS detector. Observations are consistent with standard model expectations in two signal regions that are either depleted or enriched in Z-boson decays. Upper limits at 95% confidence level are set in R-parity conserving phenomenological minimal supersymmetric and simplified models. For the simplified models, degenerate lightest chargino and next-to-lightest neutralino masses up to …

Search for scalar top quark pair production in natural gauge mediated supersymmetry models with the ATLAS detector in pp collisions at s=7 TeV

The results of a search for pair production of the lighter scalar partners of top quarks () in 2.05 fb−1 of pp collisions at TeV using the ATLAS experiment at the LHC are reported. Scalar top quar ...

Search for a heavy narrow resonance decaying to eμ, eτ, or μτ with the ATLAS detector in s=7 TeV pp collisions at the LHC

This Letter presents the results of a search for a heavy particle decaying into an e^±μ^∓e^±μ^∓, or μ^±τ^∓ final state in pp collisions at View the MathML sources=7 TeV. The data were recorded with the ATLAS detector at the LHC during 2011 and correspond to an integrated luminosity of 4.6 fb−14.6 fb^(−1). No significant excess above the Standard Model expectation is observed, and exclusions at 95% confidence level are placed on the cross section times branching ratio for the production of an R-parity-violating supersymmetric tau sneutrino. For a sneutrino mass of 500 (2000) GeV, the observed limits on the production cross section times branching ratio are 3.2 (1.4) fb, 42 (17) fb, and 40 (1…

Search for a Supersymmetric Partner to the Top Quark in Final States with Jets and Missing Transverse Momentum ats=7  TeVwith the ATLAS Detector

A search for direct pair production of supersymmetric top squarks ((t) over tilde (1)) is presented, assuming the (t) over tilde (1) decays into a top quark and the lightest supersymmetric particle, (chi) over tilde (0)(1), and that both top quarks decay to purely hadronic final states. A total of 16 (4) events are observed compared to a predicted standard model background of 13.5(-3.6)(+3.7) (4.4(-1.3)(+1.7)) events in two signal regions based on integral Ldt = 4.7 fb(-1) of pp collision data taken at root s = 7 TeV with the ATLAS detector at the LHC. An exclusion region in the (t) over tilde (1) versus (chi) over tilde (0)(1) mass plane is evaluated: 370 1) 10) similar to 0 GeV while m((t…

Measurement of the production cross section of jets in association with a Z boson in pp collisions at $\sqrt{s}$ = 7 TeV with the ATLAS detector

Measurements of the production of jets of particles in association with a Z boson in pp collisions at s√ = 7 TeV are presented, using data corresponding to an integrated luminosity of 4.6 fb[superscript −1] collected by the ATLAS experiment at the Large Hadron Collider. Inclusive and differential jet cross sections in Z events, with Z decaying into electron or muon pairs, are measured for jets with transverse momentum p [subscript T] > 30 GeV and rapidity |y| < 4.4. The results are compared to next-to-leading-order perturbative QCD calculations, and to predictions from different Monte Carlo generators based on leading-order and next-to-leading-order matrix elements supplemented by parton sh…

ATLAS measurements of the properties of jets for boosted particle searches

Measurements are presented of the properties of high transverse momentum jets, produced in proton-proton collisions at a center-of-mass energy of √s=7  TeV. The data correspond to an integrated luminosity of 35  pb−1 and were collected with the ATLAS detector in 2010. Jet mass, width, eccentricity, planar flow and angularity are measured for jets reconstructed using the anti-kt algorithm with distance parameters R=0.6 and 1.0, with transverse momentum pT>300  GeV and pseudorapidity |η|<2. The measurements are compared to the expectations of Monte Carlo generators that match leading-logarithmic parton showers to leading-order, or next-to-leading-order, matrix elements. The generators describ…

Search for a heavy neutral particle decaying into an electron and a muon using 1 fb−1 of ATLAS data

A search is presented for a high mass neutral particle that decays directly to the e±μ∓ final state. The data sample was recorded by the ATLAS detector in s√=7~TeVpp collisions at the LHC from March to June 2011 and corresponds to an integrated luminosity of 1.07 fb−1. The data are found to be consistent with the Standard Model background. The high e±μ∓ mass region is used to set 95% confidence level upper limits on the production of two possible new physics processes: tau sneutrinos in an R-parity violating supersymmetric model and Z′-like vector bosons in a lepton flavor violating model.

Observation of a NewχbState in Radiative Transitions toΥ(1S)andΥ(2S)at ATLAS

The χb(nP) quarkonium states are produced in proton-proton collisions at the Large Hadron Collider at √s=7  TeV and recorded by the ATLAS detector. Using a data sample corresponding to an integrated luminosity of 4.4  fb-1, these states are reconstructed through their radiative decays to Υ(1S,2S) with Υ→μ+μ-. In addition to the mass peaks corresponding to the decay modes χb(1P,2P)→Υ(1S)γ, a new structure centered at a mass of 10.530±0.005(stat)±0.009(syst)  GeV is also observed, in both the Υ(1S)γ and Υ(2S)γ decay modes. This structure is interpreted as the χb(3P) system.

Searches for scalar top and scalar bottom quarks at LEP2

Searches for scalar top and bottom quarks have been performed with data collected by the ALEPH detector at LEP. The data sample consists of 21.7 pb^-1 taken at sqrt{s} = 161, 170, and 172~GeV and 5.7 pb^-1 taken at sqrt{s} = 130 and 136~GeV. No evidence for scalar top quarks or scalar bottom quarks was found in the channels stop --&gt; c chi, stop --&gt; b l snu, and sbottom --&gt; b chi. For the channel stop --&gt; c chi a limit of 67 GeV/c^2 has been set on the scalar top quark mass, independent of the mixing angle between the supersymmetric partners of the left and right-handed states of the top quark. This limit assumes a mass difference between the stop and the chi of at least 10 GeV/c…

Measurement of the branching ratio and an upper limit on

Abstract Using 1.45 million hadronic Z decays collected by the ALEPH experiment at LEP, the b → τ − ν - τ X branching ratio is measured to be 2.75 ± 0.30 ± 0.37%. In addition an upper limit of 1.8 × 10 −3 at 90% confidence level is placed upon the exclusive branching ratio of B − → τ − ν - τ . These measurements are consistent with SM expectations, and put the constraint tan β M h ± GeV −1 at 90% confidence level on all Type II two Higgs doublet models (such as the MSSM).

Multi-channel search for squarks and gluinos in root s=7 TeV pp collisions with the ATLAS detector at the LHC

A search for supersymmetric particles in final states with zero, one, and two leptons, with and without jets identified as originating from b-quarks, in 4.7 fb[superscript −1] of √s = 7 TeV pp collisions produced by the Large Hadron Collider and recorded by the ATLAS detector is presented. The search uses a set of variables carrying information on the event kinematics transverse and parallel to the beam line that are sensitive to several topologies expected in supersymmetry. Mutually exclusive final states are defined, allowing a combination of all channels to increase the search sensitivity. No deviation from the Standard Model expectation is observed. Upper limits at 95 % confidence level…

Measurement of the top quark charge in pp collisions at sqrt(s) = 7 TeV with the ATLAS detector

A measurement of the top quark electric charge is carried out in the ATLAS experiment at the Large Hadron Collider using 2.05 fb[superscript −1] of data at a centre-of-mass energy of 7 TeV. In units of the elementary electric charge, the top quark charge is determined to be 0.64 ± 0.02 (stat.) ± 0.08 (syst.) from the charges of the top quark decay products in single lepton t[¯ over t] candidate events. This excludes models that propose a heavy quark of electric charge −4/3, instead of the Standard Model top quark, with a significance of more than 8σ.

Observation and Measurement of Forward Proton Scattering in Association with Lepton Pairs Produced via the Photon Fusion Mechanism at ATLAS

The observation of forward proton scattering in association with lepton pairs (eþe− þ p or μþμ− þ p) produced via photon fusion is presented. The scattered proton is detected by the ATLAS Forward Proton spectrometer, while the leptons are reconstructed by the central ATLAS detector. Proton-proton collision data recorded in 2017 at a center-of-mass energy of ffiffiffi s p ¼ 13 TeV are analyzed, corresponding to an integrated luminosity of 14.6 fb−1. A total of 57 (123) candidates in the ee þ p (μμ þ p) final state are selected, allowing the background-only hypothesis to be rejected with a significance exceeding 5 standard deviations in each channel. Proton-tagging techniques are introduced f…

Search for new particles decaying to ZZ using final states with leptons and jets with the ATLAS detector in s=7 TeV proton–proton collisions

A search is presented for a narrow resonance decaying to a pair of Z bosons using data corresponding to 1.02 fb(-1) of integrated luminosity collected by the ATLAS experiment from pp collisions at ...

Search for invisible Higgs boson decays in vector boson fusion at s=13TeV with the ATLAS detector

We report a search for Higgs bosons that are produced via vector boson fusion and subsequently decay into invisible particles. The experimental signature is an energetic jet pair with invariant mass of O(1)TeV and O(100)GeV missing transverse momentum. The analysis uses 36.1 fb −1 of pp collision data at s=13TeV recorded by the ATLAS detector at the LHC. In the signal region the 2252 observed events are consistent with the background estimation. Assuming a 125GeV scalar particle with Standard Model cross sections, the upper limit on the branching fraction of the Higgs boson decay into invisible particles is 0.37 at 95% confidence level where 0.28 was expected. This limit is interpreted in H…

Search for resonant WZ production in the fully leptonic final state in proton–proton collisions at s=13TeV with the ATLAS detector

A search for a heavy resonance decaying into WZ in the fully leptonic channel (electrons and muons) is performed. It is based on proton–proton collision data collected by the ATLAS experiment at the Large Hadron Collider at a centre-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 36.1 fb −1 . No significant excess is observed over the Standard Model predictions and limits are set on the production cross section times branching ratio of a heavy vector particle produced either in quark–antiquark fusion or through vector-boson fusion. Constraints are also obtained on the mass and couplings of a singly charged Higgs boson, in the Georgi–Machacek model, produced through ve…

Hunt for new phenomena using large jet multiplicities and missing transverse momentum with ATLAS in 4.7 fb[superscript −1] of √s = 7 TeV proton-proton collisions

Results are presented of a search for new particles decaying to large numbers of jets in association with missing transverse momentum, using 4.7 fb[superscript −1] of pp collision data at √s = 7 TeV collected by the ATLAS experiment at the Large Hadron Collider in 2011. The event selection requires missing transverse momentum, no isolated electrons or muons, and from ≥6 to ≥9 jets. No evidence is found for physics beyond the Standard Model. The results are interpreted in the context of a MSUGRA/CMSSM supersymmetric model, where, for large universal scalar mass m [subscript 0], gluino masses smaller than 840 GeV are excluded at the 95% confidence level, extending previously published limits.…

Final results of the searches for neutral Higgs bosons in e+e- collisions at sqrt(s) up to 209GeV

The final results of the ALEPH search for the Standard Model Higgs boson at LEP, with data collected in the year 2000 at centre-of-mass energies up to 209 GeV, are presented. The changes with respect to the preceding publication are described and a complete study of systematic effects is reported. The findings of this final analysis confirm the preliminary results published in November 2000 shortly after the closing down of the LEP collider: a significant excess of events is observed, consistent with the production of a $115 \Gcs$ Standard Model Higgs boson. The final results of the searches for the neutral Higgs bosons of the MSSM are also reported, in terms of limits on $\mh$, $\mA$ and $…

Evidence for the production of three massive vector bosons with the ATLAS detector

A search for the production of three massive vector bosons in proton–proton collisions is performed using data at TeV recorded with the ATLAS detector at the Large Hadron Collider in the years 2015–2017, corresponding to an integrated luminosity of 79.8 fb−1. Events with two same-sign leptons ℓ (electrons or muons) and at least two reconstructed jets are selected to search for . Events with three leptons without any same-flavour opposite-sign lepton pairs are used to search for , while events with three leptons and at least one same-flavour opposite-sign lepton pair and one or more reconstructed jets are used to search for . Finally, events with four leptons are analysed to search for and .…

Measurement of inclusive jet and dijet cross sections in proton-proton collisions at 7 TeV centre-of-mass energy with the ATLAS detector

Jet cross sections have been measured for the first time in proton-proton collisions at a centre-of-mass energy of 7 TeV using the ATLAS detector. The measurement uses an integrated luminosity of 17 nb−1 recorded at the Large Hadron Collider. The anti-k t algorithm is used to identify jets, with two jet resolution parameters, R=0.4 and 0.6. The dominant uncertainty comes from the jet energy scale, which is determined to within 7% for central jets above 60 GeV transverse momentum. Inclusive single-jet differential cross sections are presented as functions of jet transverse momentum and rapidity. Dijet cross sections are presented as functions of dijet mass and the angular variable χ. The res…

Measurement ofD*±meson production in jets fromppcollisions ats=7  TeVwith the ATLAS detector

This paper reports a measurement of D*(+/-) meson production in jets from proton- proton collisions at a center- of- mass energy of root s = 7 TeV at the CERN Large Hadron Collider. The measurement is based on a data sample recorded with the ATLAS detector with an integrated luminosity of 0.30 pb(-1) for jets with transverse momentum between 25 and 70 GeV in the pseudorapidity range vertical bar eta vertical bar D-0 pi(+), D-0 -> K-pi(+), and its charge conjugate. The production rate is found to be N(D*(+/-))/N(jet) = 0.025 +/- 0.001(stat.) +/- 0.004(syst.) for D*(+/-) mesons that carry a fraction z of the jet momentum in the range 0.3< z< 1. Monte Carlo predictions fail to describe the dat…

Search for high-mass resonances decaying to dilepton final states in pp collisions at √s = 7 TeV with the ATLAS detector

The ATLAS detector at the Large Hadron Collider is used to search for high-mass resonances decaying to an electron-positron pair or a muon-antimuon pair. The search is sensitive to heavy neutral Z′ gauge bosons, Randall-Sundrum gravitons, Z [superscript *] bosons, techni-mesons, Kaluza-Klein Z/γ bosons, and bosons predicted by Torsion models. Results are presented based on an analysis of pp collisions at a center-of-mass energy of 7 TeV corresponding to an integrated luminosity of 4.9 fb[superscript −1] in the e [superscript +] e [superscript −] channel and 5.0 fb[superscript −1] in the μ [superscript +] μ [superscript −] channel. A Z [superscript ′] boson with Standard Model-like couplings…

Search for the glueball candidates f0(1500) and fJ(1710) in γγ collisions

Abstract Data taken with the ALEPH detector at LEP1 have been used to search for γγ production of the glueball candidates f0(1500) and fJ(1710) via their decay to π+π−. No signal is observed and upper limits to the product of γγ width and π+π− branching ratio of the f0(1500) and the fJ(1710) have been measured to be Γ(γγ→f 0 (1500))· B R (f 0 (1500)→π + π − ) keV and Γ(γγ→f J (1710))· B R (f J (1710)→π + π − ) keV at 95% confidence level.

Inclusive production of neutral pions in hadronic Z decays

A measurement of the inclusive production of pi(0) mesons in hadronic Z decays is presented and compared to Monte Carlo model predictions. The analysis is based on approximately 2 million hadronic events recorded with the ALEPH detector at LEP at a centre-of-mass energy of root s = 91.2 GeV. Neutral pions are reconstructed using photons measured in the electromagnetic calorimeter and photons from conversion pairs. The inclusive pi(0) momentum spectrum is measured in the range 0.025 < x(p) = p/p(beam) < 1. In this range the number of pi(0) per hadronic Z is found to be 4.80 +/- 0.07(stat) +/- 0.31(sys). The differential inclusive pi(0) cross section is also measured as a function of transver…

Search for a heavy charged boson in events with a charged lepton and missing transverse momentum from pp collisions at s=13  TeV with the ATLAS detector

A search for a heavy charged-boson resonance decaying into a charged lepton (electron or muon) and a neutrino is reported. A data sample of 139  fb−1 of proton-proton collisions at √s=13  TeV collected with the ATLAS detector at the LHC during 2015–2018 is used in the search. The observed transverse mass distribution computed from the lepton and missing transverse momenta is consistent with the distribution expected from the Standard Model, and upper limits on the cross section for pp→W′→lν are extracted (l=e or μ). These vary between 1.3 pb and 0.05 fb depending on the resonance mass in the range between 0.15 and 7.0 TeV at 95% confidence level for the electron and muon channels combined. …

Study of heavy-flavor quarks produced in association with top-quark pairs at s=7  TeV using the ATLAS detector

Using a sample of dilepton top-quark pair ((tt) over bar) candidate events, a study is performed of the production of top-quark pairs together with heavy-flavor (HF) quarks, the sum of (tt) over bar + b + X and (tt) over bar + c + X, collectively referred to as (tt) over bar + HF. The data set used corresponds to an integrated luminosity of 4.7 fb(-1) of proton-proton collisions at a center-of-mass energy of 7 TeV recorded by the ATLAS detector at the CERN Large Hadron Collider. The presence of additional HF (b or c) quarks in the (tt) over bar sample is inferred by looking for events with at least three b-tagged jets, where two are attributed to the b quarks from the (tt) over bar decays a…

Search for Supersymmetry inppCollisions ats=7  TeVin Events with Two Photons and Missing Transverse Energy

A search for supersymmetry in the context of general gauge-mediated breaking with the lightest neutralino as the next-to-lightest supersymmetric particle and the gravitino as the lightest is presented. The data sample corresponds to an integrated luminosity of 36 pb(-1) recorded by the CMS experiment at the LHC. The search is performed by using events containing two or more isolated photons, at least one hadronic jet, and significant missing transverse energy. No excess of events at high missing transverse energy is observed. Upper limits on the signal cross section for general gauge-mediated supersymmetry between 0.3 and 1.1 pb at the 95% confidence level are determined for a range of squa…

Search for anomalous production of prompt like-sign muon pairs and constraints on physics beyond the Standard Model with the ATLAS detector

An inclusive search for anomalous production of two prompt, isolated muons with the same electric charge is presented. The search is performed in a data sample corresponding to 1.6  fb−1 of integrated luminosity collected in 2011 at √s=7  TeV with the ATLAS detector at the LHC. Muon pairs are selected by requiring two isolated muons of the same electric charge with pT>20  GeV and |η|<2.5. Minimal requirements are placed on the rest of the event activity. The distribution of the invariant mass of the muon pair m(μμ) is found to agree well with the background expectation. Upper limits on the cross section for anomalous production of two muons with the same electric charge are placed as a func…

Search for long-lived, heavy particles in final states with a muon and multi-track displaced vertex in proton–proton collisions at s=7 TeV with the ATLAS detector

Many extensions of the Standard Model posit the existence of heavy particles with long lifetimes. In this Letter, results are presented of a search for events containing one or more such particles, which decay at a significant distance from their production point, using a final state containing charged hadrons and an associated muon. This analysis uses a data sample of proton-proton collisions at root s = 7 TeV corresponding to an integrated luminosity of 4.4 fb(-1) collected in 2011 by the ATLAS detector operating at the Large Hadron Collider. Results are interpreted in the context of R-parity violating supersymmetric scenarios. No events in the signal region are observed and limits are se…

Observation of charmless hadronic B decays

Four candidates for charmless hadronic B decay are observed in a data sample of four million hadronic Z decays recorded by the ALEPH detector at LEP. The probability that these events come from background sources is estimated to be less than 10(-6). The average branching of weakly decaying B hadrons (a mixture of B-d(0), B-s(0) and Lambda(b) weighted by their production The average branching ratio of weakly decaying B hadrons (a mixture of B-d(0) cross sections and lifetimes, here denoted B) into two long-lived charged hadrons (pions, kaons or protons) is measured to be Br(B-->h(+)h(-))=(1.7(-0.7)(+1.0)+/-0.2)x10(-5). The relative branching fraction Br(B-d(s)(0)-->pi(+)pi(-)(K-))/Br(B-d(s)(…

Search for FCNC single top-quark production at s=7 TeV with the ATLAS detector

A search for the production of single top-quarks via flavour-changing neutral-currents is presented. Data collected with the ATLAS detector at a centre-of-mass energy of root s = 7 TeV, correspondi ...

Fermi-Dirac correlations in Lambda pairs in hadronic Z decays

Two-particle correlations of Lambda Lambda and pairs have been studied in multihadronic Z decays recorded with the ALEPH detector at LEP in the years from 1992 to 1995. The correlations were measured as a function of the four-momentum difference Q of the pair. A depletion of events is observed in the region Q 2 GeV the fraction of pairs with spin one is consistent with the value of 0.75 expected for a statistical spin mixture, whilst for Q pairs, where no Fermi-Dirac correlations are expected, the spin one fraction is measured to be consistent with 0.75 over the entire analysed Q range. (C) 2000 Elsevier Science B.V. All rights reserved.

Measurement of the strong coupling constant using τ decays

The strong coupling constant is determined from the leptonic branching ratios, the lifetime, and the invariant mass distribution of the hadronic final state of the tau lepton, using data accumulated at LEP with the ALEPH detector. The strong coupling constant measurement, alpha(s), (m(tau)2) = 0.330 +/-0.046, evolved to the Z mass, yields alpha(s)(M(Z)2) = 0. 1 18 +/- 0.005. The error includes experimental and theoretical uncertainties, the latter evaluated in the framework of the Shifman, Vainshtein and Zakharov (SVZ) approach. The method allows the non-perturbative contribution to the hadronic decay rate to be determined to be 0.3 +/- 0.5% . RI Perrier, Frederic/A-5953-2011; ANTONELLI, AN…

Single hadron response measurement and calorimeter jet energy scale uncertainty with the ATLAS detector at the LHC

The uncertainty on the calorimeter energy response to jets of particles is derived for the ATLAS experiment at the Large Hadron Collider (LHC). First, the calorimeter response to single isolated charged hadrons is measured and compared to the Monte Carlo simulation using proton-proton collisions at centre-of-mass energies of √s = 900 GeV and 7 TeV collected during 2009 and 2010. Then, using the decay of Ks and Λ particles, the calorimeter response to specific types of particles (positively and negatively charged pions, protons, and anti-protons) is measured and compared to the Monte Carlo predictions. Finally, the jet energy scale uncertainty is determined by propagating the response uncert…

The ATLAS Inner Detector commissioning and calibration

The ATLAS Inner Detector is a composite tracking system consisting of silicon pixels, silicon strips and straw tubes in a 2 T magnetic field. Its installation was completed in August 2008 and the detector took part in data-taking with single LHC beams and cosmic rays. The initial detector operation, hardware commissioning and insitu calibrations are described. Tracking performance has been measured with 7.6 million cosmic-ray events, collected using a tracking trigger and reconstructed with modular pattern-recognition and fitting software. The intrinsic hit efficiency and tracking trigger efficiencies are close to 100%. Lorentz angle measurements for both electrons and holes, specific energ…

Study of energy response and resolution of the ATLAS barrel calorimeter to hadrons of energies from 20 to 350 GeV

A fully instrumented slice of the ATLAS detector was exposed to test beams from the SPS (Super Proton Synchrotron) at CERN in 2004. In this paper, the results of the measurements of the response of the barrel calorimeter to hadrons with energies in the range 20 to 350 GeV and beam impact points and angles corresponding to pseudorapidity values in the range 0.2-0.65 are reported. The results are compared to the predictions of a simulation program using the Geant 4 toolkit.

Measurement of differentialJ/ψproduction cross sections and forward-backward ratios inp + Pbcollisions with the ATLAS detector

Measurements of differential cross sections for J/psi production in p + Pb collisions at root S-NN= 5.02 TeV at the CERN Large Hadron Collider with the ATLAS detector are presented. The data set us ...

Observation of Electroweak Production of a Same-Sign W Boson Pair in Association with Two Jets in pp Collisions at s=13  TeV with the ATLAS Detector

This Letter presents the observation and measurement of electroweak production of a same-sign W boson pair in association with two jets using 36.1  fb^{-1} of proton-proton collision data recorded at a center-of-mass energy of sqrt[s]=13  TeV by the ATLAS detector at the Large Hadron Collider. The analysis is performed in the detector fiducial phase-space region, defined by the presence of two same-sign leptons, electron or muon, and at least two jets with a large invariant mass and rapidity difference. A total of 122 candidate events are observed for a background expectation of 69±7 events, corresponding to an observed signal significance of 6.5 standard deviations. The measured fiducial s…

Measurement of the centrality dependence of J/ψ yields and observation of Z production in lead–lead collisions with the ATLAS detector at the LHC

Using the ATLAS detector, a centrality-dependent suppression has been observed in the yield of J/psi mesons produced in the collisions of lead ions at the Large Hadron Collider. In a sample of minimum-bias lead-lead collisions at a nucleon-nucleon centre of mass energy root s(NN) = 2.76 TeV, corresponding to an integrated luminosity of about 6.7 mu b(-1), J/psi mesons are reconstructed via their decays to mu(+)mu(-) pairs. The measured J/psi yield, normalized to the number of binary nucleon-nucleon collisions, is found to significantly decrease from peripheral to central collisions. The centrality dependence is found to be qualitatively similar to the trends observed at previous, lower ener…

Search for massive long-lived highly ionising particles with the ATLAS detector at the LHC

A search is made for massive highly ionising particles with lifetimes in excess of 100 ns, with the ATLAS experiment at the Large Hadron Collider, using 3.1 pb-1 of pp collision data taken at √s = 7TeV. The signature of energy loss in the ATLAS inner detector and electromagnetic calorimeter is used. No such particles are found and limits on the production cross section for electric charges 6e ≤ |q| ≤ 17e and masses 200 GeV ≤ m ≤ 1000 GeV are set in the range 1–12 pb for different hypotheses on the production mechanism.

Search for Down-Type Fourth Generation Quarks with the ATLAS Detector in Events with One Lepton and Hadronically Decaying W Bosons

This Letter presents a search for pair production of heavy down-type quarks decaying via b′→Wt in the lepton+jets channel, as b′¯b′→W−tW+¯t→b¯bW+W−W+W−→l±νb¯bq¯qq¯qq¯q. In addition to requiring exactly one lepton, large missing transverse momentum, and at least six jets, the invariant mass of nearby jet pairs is used to identify high transverse momentum W bosons. In data corresponding to an integrated luminosity of 1.04  fb−1 from pp collisions at √s=7  TeV recorded with the ATLAS detector, a heavy down-type quark with mass less than 480 GeV can be excluded at the 95% confidence level.

Measurement of photon?jet transverse momentum correlations in 5.02 TeV Pb + Pb and pp collisions with ATLAS

Jets created in association with a photon can be used as a calibrated probe to study energy loss in the medium created in nuclear collisions. Measurements of the transverse momentum balance between isolated photons and inclusive jets are presented using integrated luminosities of 0.49 nb−1 of Pb + Pb collision data at TeV and 25 pb−1 of pp collision data at TeV recorded with the ATLAS detector at the LHC. Photons with transverse momentum GeV and are paired with all jets in the event that have GeV and pseudorapidity . The transverse momentum balance given by the jet-to-photon ratio, , is measured for pairs with azimuthal opening angle . Distributions of the per-photon jet yield as a function…

Study of jet shapes in inclusive jet production inppcollisions ats=7  TeVusing the ATLAS detector

Jet shapes have been measured in inclusive jet production in proton-proton collisions at root s = 7 TeV using 3 pb(-1) of data recorded by the ATLAS experiment at the LHC. Jets are reconstructed using the anti-k(t) algorithm with transverse momentum 30 GeV < p(T) < 600 GeV and rapidity in the region vertical bar y vertical bar < 2.8. The data are corrected for detector effects and compared to several leading-order QCD matrix elements plus parton shower Monte Carlo predictions, including different sets of parameters tuned to model fragmentation processes and underlying event contributions in the final state. The measured jets become narrower with increasing jet transverse momentum and the je…

Measurement of the D∗± cross section in two photon collisions at LEP

Abstract The inclusive production of D ∗± mesons in photon-photon collisions has been measured by the Aleph experiment at LEP with a beam energy of 45 GeV. The D ∗+ are detected in their decay to D 0 π + with the D 0 observed in three separate decay modes: (1) K − π + , (2) K − π + π 0 and (3) K − π + π − π + , and analagously for the D ∗− modes. A total of 33 events was observed from an integrated luminosity of 73 pb −1 which corresponds to a cross section for Σ( e + e − → e + e − D ∗± X ) of 155 ± 33 ± 21 pb. This result is compatible with both the direct production γγ → c c in the Born approximation and with a more complete calculation which includes both radiative QCD corrections and co…

Monitoring and data quality assessment of the ATLAS liquid argon calorimeter

The liquid argon calorimeter is a key component of the ATLAS detector installed at the CERN Large Hadron Collider. The primary purpose of this calorimeter is the measurement of electron and photon kinematic properties. It also provides a crucial input for measuring jets and missing transverse momentum. An advanced data monitoring procedure was designed to quickly identify issues that would affect detector performance and ensure that only the best quality data are used for physics analysis. This article presents the validation procedure developed during the 2011 and 2012 LHC data-taking periods, in which more than 98% of the proton-proton luminosity recorded by ATLAS at a centre-of-mass ener…

Search for dark matter in events with heavy quarks and missing transverse momentum in [Formula: see text] collisions with the ATLAS detector.

This article reports on a search for dark matter pair production in association with bottom or top quarks in \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$20.3 \mathrm {~fb}^{-1}$$\end{document}20.3fb-1 of \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$pp$$\end{document}pp collisions collected at \documentclass[12pt]{minimal} \use…

Search for decays of stopped, long-lived particles from 7 TeV pp collisions with the ATLAS detector

New metastable massive particles with electric and colour charge are features of many theories beyond the Standard Model. A search is performed for long-lived gluino-based R-hadrons with the ATLAS detector at the LHC using a data sample corresponding to an integrated luminosity of 31 pb[superscript −1]. We search for evidence of particles that have come to rest in the ATLAS detector and decay at some later time during the periods in the LHC bunch structure without proton–proton collisions. No significant deviations from the expected backgrounds are observed, and a cross-section limit is set. It can be interpreted as excluding gluino-based R-hadrons with masses less than 341 GeV at the 95 % …

Measurement of D⁎±, D± and Ds± meson production cross sections in pp collisions at s=7 TeV with the ATLAS detector

The production of D*(+/-), D-+/- and D-S(+/-) charmed mesons has been measured with the ATLAS detector in pp collisions at,/7s = 7 TeV at the LHC, using data corresponding to an integrated luminosi ...

Search for Scalar Bottom Quark Pair Production with the ATLAS Detector inppCollisions ats=7  TeV

The results of a search for pair production of the scalar partners of bottom quarks in 2: 05 fb(-1) of pp collisions at root s = 7 TeV using the ATLAS experiment are reported. Scalar bottom quarks ...

Measurement of inclusive jet and dijet production inppcollisions ats=7  TeVusing the ATLAS detector

Inclusive jet and dijet cross sections have been measured in proton-proton collisions at a centre-of-mass energy of 7 TeV using the ATLAS detector at the Large Hadron Collider. The cross sections were measured using jets clustered with the anti-kT algorithm with parameters R=0.4 and R=0.6. These measurements are based on the 2010 data sample, consisting of a total integrated luminosity of 37 inverse picobarns. Inclusive jet double-differential cross sections are presented as a function of jet transverse momentum, in bins of jet rapidity. Dijet double-differential cross sections are studied as a function of the dijet invariant mass, in bins of half the rapidity separation of the two leading …

Measurement of the production cross section for W-bosons in association with jets in pp collisions at s=7 TeV with the ATLAS detector

This Letter reports on a first measurement of the inclusive W + jets cross section in proton-proton collisions at a centre-of-mass energy of 7 TeV at the LHC, with the ATLAS detector. Cross section ...

Measurement of $ZZ$ production in $pp$ collisions at $\sqrt{s}=7$ TeV and limits on anomalous $ZZZ$ and $ZZ\gamma$ couplings with the ATLAS detector

Journal of High Energy Physics 2013.3 (2013): 128 reproduced by permission of Scuola Internazionale Superiore di Studi Avanzati (SISSA)

Search for events with large missing transverse momentum, jets, and at least two tau leptons in 7 TeV proton–proton collision data with the ATLAS detector

A search for events with large missing transverse momentum, jets, and at least two tau leptons has been performed using 2 fb[superscript −1] of proton–proton collision data at √s = 7 TeV recorded with the ATLAS detector at the Large Hadron Collider. No excess above the Standard Model background expectation is observed and a 95% CL upper limit on the visible cross section for new phenomena is set, where the visible cross section is defined by the product of cross section, branching fraction, detector acceptance and event selection efficiency. A 95% CL lower limit of 32 TeV is set on the gauge-mediated supersymmetry breaking (GMSB) scale Λ independent of tan β. These limits provide the most s…

Inclusive search for same-sign dilepton signatures in pp collisions at $ sqrt {s} = 7 $ TeV with the ATLAS detector

An inclusive search is presented for new physics in events with two isolated leptons (e or mu) having the same electric charge. The data are selected from events collected from p p collisions at root s = 7 TeV by the ATLAS detector and correspond to an integrated luminosity of 34 pb(-1). The spectra in dilepton invariant mass, missing transverse momentum and jet multiplicity are presented and compared to Standard Model predictions. In this event sample, no evidence is found for contributions beyond those of the Standard Model. Limits are set on the cross-section in a fiducial region for new sources of same-sign high-mass dilepton events in the ee, e mu and mu mu channels. Four models predic…

Search for Pair Production of a Heavy Up-Type Quark Decaying to aWBoson and abQuark in thelepton+jetsChannel with the ATLAS Detector

A search is presented for production of a heavy up-type quark (t') together with its antiparticle, assuming subsequent decay to a W boson and a b quark, t'(t) over bar' -> W(+)bW(-)(b) over bar. The search is based on 1.04 fb(-1) of proton-proton collisions at root s = 7 TeV collected by the ATLAS detector at the CERN Large Hadron Collider. Data are analyzed in the lepton + jets final state, characterized by a high transverse momentum isolated electron or muon, high missing transverse momentum, and at least three jets. No significant excess of events above the background expectation is observed. A 95% C.L. lower limit of 404 GeV is set for the mass of the t' quark.

Combination of searches for heavy resonances decaying into bosonic and leptonic final states using 36  fb−1 of proton-proton collision data at s=13  TeV with the ATLAS detector

Searches for new heavy resonances decaying into different pairings of W, Z, or Higgs bosons, as well as dirffiffiffiectly into leptons, are presented using a data sample corresponding to 36.1 fb(-1 ...

Measurement of the

A new method is presented for the measurement of the mean $\tau$ lepton lifetime using events in which $\tau$'s are pair-produced and both $\tau$'s decay to hadrons and $\nu_\tau$. Based on the correlation between the two $\tau$'s produced at a symmetric $e^+ e^-$ collider, the 3DIP method relies on the three-dimensional information from a double-sided vertex detector and on kinematic constraints for the precise measurement of the $\tau$ decay angles. Using the data collected from 1992 to 1994 with the ALEPH detector at LEP, a $\tau$ lifetime of $288.0 \pm 3.1 \pm 1.3 $\fs is obtained from the sample in which both $\tau$'s decay to one charged track, and $292.8 \pm 5.6 \pm 3.0 $\fs from the…

Ks0andΛproduction inppinteractions ats=0.9and 7 TeV measured with the ATLAS detector at the LHC

The production of K(S)(0) and Lambda hadrons is studied in pp collision data at root s = 0.9 and 7 TeV collected with the ATLAS detector at the LHC using a minimum-bias trigger. The observed distributions of transverse momentum, rapidity, and multiplicity are corrected to hadron level in a model-independent way within well-defined phase-space regions. The distribution of the production ratio of (Lambda) over bar to Lambda baryons is also measured. The results are compared with various Monte Carlo simulation models. Although most of these models agree with data to within 15% in the K(S)(0) distributions, substantial disagreements are found in the Lambda distributions of transverse momentum.

Search for Diphoton Events with Large Missing Transverse Energy with 36 pb^-1 of 7 TeV Proton-Proton Collision Data with the ATLAS Detector

Making use of 36 pb^-1 of proton-proton collision data at sqrt{s} = 7 TeV, the ATLAS Collaboration has performed a search for diphoton events with large missing transverse energy. Observing no excess of events above the Standard Model prediction, a 95% Confidence Level (CL) upper limit is set on the cross section for new physics of sigma &lt; 0.38 - 0.65 pb in the context of a generalised model of gauge mediated supersymmetry breaking (GGM) with a bino-like lightest neutralino, and of sigma &lt; 0.18 - 0.23 pb in the context of a specific model with one universal extra dimension (UED). A 95 % CL lower limit of 560 GeV, for bino masses above 50 GeV, is set on the GGM gluino mass, while a low…

Measurements of |Vcb|, form factors and branching fractions in the decays → ℓ and → ℓ

Two samples of exclusive semileptonic decays, 579 B0 -> D*+l-νl events and 261 B0 -> D+l-νl events, are selected from approximately 3.9 million hadronic Z decays collected by the ALEPH detector at LEP. From the reconstructed differential decay rate of each sample, the product of the hadronic form factor F(ω) at zero recoil of the D(*)+ meson and the CKM matrix element Vcb are measured to be FD*+ (1) Vcb = (31.9 +/- 1.8stat +/- 1.9syst) × 10-3,FD+ (1) Vcb = (27.8 +/- 6.8stat +/- 6.5syst) × 10-3. The ratio of the form factorsFD+ (1) and FD*+ (1) is measured to beFD+ (1)/FD*+ (1) = 0.87 +/- 0.22stat +/- 0.21syst. A value of Vcb is extracted from the two samples, using theoretical constraints o…

Measurements of tt¯ differential cross-sections of highly boosted top quarks decaying to all-hadronic final states in pp collisions at s=13  TeV using the ATLAS detector

Measurements are made of differential cross-sections of highly boosted pair-produced top quarks as a function of top-quark and t (t) over bar system kinematic observables using proton-proton collis ...

Measurement of the distributions of event-by-event flow harmonics in lead-lead collisions at = 2.76 TeV with the ATLAS detector at the LHC

We acknowledge the support of ANPCyT, Argentina; YerPhI, Armenia; ARC, Australia; BMWF and FWF, Austria; ANAS, Azerbaijan; SSTC, Belarus; CNPq and FAPESP, Brazil; NSERC, NRC and CFI, Canada; CERN; CONICYT, Chile; CAS, MOST and NSFC, China; COLCIENCIAS, Colombia; MSMT CR, MPO CR and VSC CR, Czech Republic; DNRF, DNSRC and Lundbeck Foundation, Denmark; EPLANET, ERC and NSRF, European Union; IN2P3-CNRS, CEA-DSM/IRFU, France; GNSF, Georgia; BMBF, DFG, HGF, MPG and AvH Foundation, Germany; GSRT and NSRF, Greece; ISF, MINERVA, GIF, DIP and Benoziyo Center, Israel; INFN, Italy; MEXT and JSPS, Japan; CNRST, Morocco; FOM and NWO, Netherlands; BRF and RCN, Norway; MNiSW, Poland; GRICES and FCT, Portu…

Search for the standard model Higgs boson

Using a data sample corresponding to about 1 233 000 hadronic Z decays collected by the ALEPH experiment at LEP, the reaction e+e- --> HZ* has been used to search for the standard model Higgs boson, in association with missing energy when Z* --> nunuBAR, or with a pair of energetic leptons when Z* --> e+e- or mu+mu-. No signal was found and, at the 95% confidence level, m(H) exceeds 58.4 GeV/c2. RI ANTONELLI, ANTONELLA/C-6238-2011; Buttar, Craig/D-3706-2011; Stahl, Achim/E-8846-2011; Passalacqua, Luca/F-5127-2011; Murtas, Fabrizio/B-5729-2012; St.Denis, Richard/C-8997-2012; Forti, Francesco/H-3035-2011; Ferrante, Isidoro/F-1017-2012

Search for high mass dilepton resonances in pp collisions at s=7 TeV with the ATLAS experiment

This Letter presents a search for high mass e(+)e(-) or mu(+)mu(-) resonances in pp collisions at root s = 7 TeV at the LHC. The data were recorded by the ATLAS experiment during 2010 and correspon ...

Study of the response of the ATLAS central calorimeter to pions of energies from 3 to 9 GeV

Çetin, Serkant Ali (Dogus Author) A fully instrumented slice of the ATLAS central detector was exposed to test beams from the SPS (Super Proton Synchrotron) at CERN in 2004. In this paper, the response of the central calorimeters to pions with energies in the range between 3 and 9 GeV is presented. The linearity and the resolution of the combined calorimetry (electromagnetic and hadronic calorimeters) was measured and compared to the prediction of a detector simulation program using the toolkit Geant 4.

Measurement of Wγ and Zγ production in proton-proton collisions at √s =7 TeV with the ATLAS detector

Artículo escrito por un elevado número de autores, solo se referencian el que aparece en primer lugar, el nombre del grupo de colaboración, si le hubiere, y los autores pertenecientes a la UAM

Search for the standard model Higgs boson at the LEP2 collider near

Abstract During 1997 the ALEPH experiment at LEP gathered 57 pb −1 of data at centre-of-mass energies near 183 GeV . These data are used to look for possible signals from the production of the Standard Model Higgs boson in the reaction e+e−→HZ. No evidence of a signal is found in the data; seven events are selected, in agreement with the expectation of 7.2 events from background processes. This observation results in an improved lower limit on the mass of the Higgs boson: m H >87.9 GeV /c 2 at 95% confidence level.

Evidence for the spin-0 nature of the Higgs boson using ATLAS data

We acknowledge the support of ANPCyT, Argentina; YerPhl, Armenia; ARC, Australia; BMWF and FWF, Austria; ANAS, Azerbaijan; SSTC, Belarus; CNPq and FAPESP, Brazil; NSERC, NRC and CFI, Canada; CERN; CONICYT, Chile; CAS, MOST and NSFC, China; COLCIENCIAS, Colombia; MSMT CR, MPO CR and VSC CR, Czech Republic; DNRF, DNSRC and Lundbeck Foundation, Denmark; EPLANET, ERC and NSRF, European Union; IN2P3-CNRS, CEA-DSM/IRFU, France; GNSF, Georgia; BMBF, DFG, HGF, MPG and AvH Foundation, Germany; GSRT and NSRF, Greece; ISF, MINERVA, GIF, DIP and Benoziyo Center, Israel; INFN, Italy; MEXT and JSPS, Japan; CNRST, Morocco; FOM and NWO, Netherlands; BRF and RCN, Norway; MNiSW, Poland; GRICES and FCT, Portu…

Search for squarks and gluinos using final states with jets and missing transverse momentum with the ATLAS detector in s=7 TeV proton–proton collisions

A search for squarks and gluinos in events containing jets, missing transverse momentum and no electrons or muons is presented. The data were recorded in 2011 by the ATLAS experiment in root s = 7 TeV proton-proton collisions at the Large Hadron Collider. No excess above the Standard Model background expectation is observed in 1.04 fb(-1) of data. Gluino and squark masses below 700 GeV and 875 GeV respectively are excluded at the 95% confidence level in simplified models containing only squarks of the first two generations, a gluino octet and a massless neutralino. The exclusion limit increases to 1075 GeV for squarks and gluinos of equal mass. In MSUGRA/CMSSM models with tan beta = 10, A(0…

Measurement of dijet production with a veto on additional central jet activity in pp collisions at sqrt(s)=7 TeV using the ATLAS detector

A measurement of jet activity in the rapidity interval bounded by a dijet system is presented. Events are vetoed if a jet with transverse momentum greater than 20 GeV is found between the two boundary jets. The fraction of dijet events that survive the jet veto is presented for boundary jets that are separated by up to six units of rapidity and with mean transverse momentum 50 < p¯T < 500 GeV. The mean multiplicity of jets above the veto scale in the rapidity interval bounded by the dijet system is also presented as an alternative method for quantifying perturbative QCD emission. The data are compared to a next-to-leading order plus parton shower prediction from the powheg-box, an all-order…

A search for new physics in dijet mass and angular distributions in pp collisions at [subscript √s=7] TeV measured with the ATLAS detector

A search for new interactions and resonances produced in LHC proton–proton (pp) collisions at a centre-of-mass energy ps = 7 TeV was performed with the ATLAS detector. Using a dataset with an integrated luminosity of 36 pb−1, dijet mass and angular distributions were measured up to dijet masses of 3.5 TeV and were found to be in good agreement with Standard Model predictions. This analysis sets limits at 95% CL on various models for new physics: an excited quark is excluded for mass between 0.60 and 2.64 TeV, an axigluon hypothesis is excluded for axigluon masses between 0.60 and 2.10 TeV and quantum black holes are excluded in models with six extra space–time dimensions for quantum gravity…

Commissioning of the ATLAS Muon Spectrometer with cosmic rays

The ATLAS detector at the Large Hadron Collider has collected several hundred million cosmic ray events during 2008 and 2009. These data were used to commission the Muon Spectrometer and to study the performance of the trigger and tracking chambers, their alignment, the detector control system, the data acquisition and the analysis programs. We present the performance in the relevant parameters that determine the quality of the muon measurement. We discuss the single element efficiency, resolution and noise rates, the calibration method of the detector response and of the alignment system, the track reconstruction efficiency and the momentum measurement. The results show that the detector i…

Readiness of the ATLAS liquid argon calorimeter for LHC collisions

The ATLAS liquid argon calorimeter has been operating continuously since August 2006. At this time, only part of the calorimeter was readout, but since the beginning of 2008, all calorimeter cells have been connected to the ATLAS readout system in preparation for LHC collisions. This paper gives an overview of the liquid argon calorimeter performance measured in situ with random triggers, calibration data, cosmic muons, and LHC beam splash events. Results on the detector operation, timing perfor-mance, electronics noise, and gain stability are presented. High energy deposits from radiative cosmic muons and beam splash events allow to check the intrinsic constant term of the energy resolutio…

Search for Quantum Black Hole Production in High-Invariant-MassLepton+JetFinal States UsingppCollisions ats=8  TeVand the ATLAS Detector

This Letter presents a search for quantum black-hole production using 20.3 fb(-1) of data collected with the ATLAS detector in pp collisions at the LHC at root s = 8 TeV. The quantum black holes are assumed to decay into a final state characterized by a lepton (electron or muon) and a jet. In either channel, no event with a lepton-jet invariant mass of 3.5 TeV or more is observed, consistent with the expected background. Limits are set on the product of cross sections and branching fractions for the lepton + jet final states of quantum black holes produced in a search region for invariant masses above 1 TeV. The combined 95% confidence level upper limit on this product for quantum black hol…

Operational experience with a large detector system using silicon strip detectors with double sided readout

Abstract A large system of silicon strip detectors with double sided readout has been successfully commissioned over the course of the last year at the e + e − collider LEP. The readout of this 73 728 channel system is performed with custom designed VLSI charge sensitive amplifier chips (CAMEX64A). An overall point resolution of 12 μm on both sides has been acheived for the complete system. The most important difficulties during the run were beam losses into the detector, and a chemical agent deposited onto the electronics; however, the damage from these sources was understood and brought under control. This and other results of the 1991 data-taking run are described with special emphasis o…

Search for second generation scalar leptoquarks in $pp$ collisions at $\sqrt{s}=7$ TeV with the ATLAS detector

The results of a search for the production of second generation scalar leptoquarks are presented for final states consisting of either two muons and at least two jets or a muon plus missing transverse momentum and at least two jets. A total of 1.03 fb−1 integrated luminosity of proton-proton collision data produced by the Large Hadron Collider at \(\sqrt{s}=7~\mbox{TeV}\) and recorded by the ATLAS detector is used for the search. The event yields in the signal regions are found to be consistent with the Standard Model background expectations. The production of second generation leptoquarks is excluded for a leptoquark mass mLQ<594 (685) GeV at 95 % confidence level, for a branching ratio of…

A study of the decay width difference in the B0s– system using φφ correlations

In a data sample of about four million hadronic Z decays recorded with the ALEPH detector from 1991 to 1995, the decay is observed, based on tagging the final state with two φ mesons in the same hemisphere. The final state is mostly CP even and corresponds to the short-lived B0s mass eigenstate. The branching ratio of this decay is measured to be . A measurement of the lifetime of the B0s(short) gives 1.27±0.33±0.08 ps. The lifetime and branching ratio measurements provide two essentially independent methods of estimating the relative decay width difference ΔΓ/Γ in the B0s– system, corresponding to an average value ΔΓ/Γ=(25+21−14)%.

Search for Direct Top Squark Pair Production in Final States with One Isolated Lepton, Jets, and Missing Transverse Momentum ins=7  TeVppCollisions Using4.7  fb−1of ATLAS Data

A search is presented for direct top squark pair production in final states with one isolated electron or muon, jets, and missing transverse momentum in proton-proton collisions at root s = 7 TeV. The measurement is based on 4.7 fb(-1) of data collected with the ATLAS detector at the LHC. Each top squark is assumed to decay to a top quark and the lightest supersymmetric particle (LSP). The data are found to be consistent with standard model expectations. Top squark masses between 230 GeV and 440 GeV are excluded with 95% confidence for massless LSPs, and top squark masses around 400 GeV are excluded for LSP masses up to 125 GeV.

Measurement of the inclusive isolated prompt photon cross-section in pp collisions at s=7 TeV using 35 pb−1 of ATLAS data

A measurement of the differential cross-section for the inclusive production of isolated prompt photons in pp collisions at a center-of-mass energy root s = 7 TeV is presented. The measurement cove ...

Search for pair production of first or second generation leptoquarks in proton-proton collisions ats=7  TeVusing the ATLAS detector at the LHC

This paper describes searches for the pair production of first or second generation scalar leptoquarks using 35 pb(-1) of proton-proton collision data recorded by the ATLAS detector at root s = 7 TeV. Leptoquarks are searched in events with two oppositely-charged muons or electrons and at least two jets, and in events with one muon or electron, missing transverse momentum and at least two jets. After event selection, the observed yields are consistent with the predicted backgrounds. Leptoquark production is excluded at the 95% CL for masses M-LQ < 376 (319) GeV and M-LQ < 422 (362) GeV for first and second generation scalar leptoquarks, respectively, when assuming the branching fraction of …

Search for pair-produced heavy quarks decaying toWqin the two-lepton channel at(s)=7  TeVwith the ATLAS detector

A search is presented for heavy-quark pair production (Q (Q) over bar) under the decay hypothesis Q (Q) over bar -> W(+)qW(-)(q) over bar with q = d, s, b for up-type Q or q = u, c for down-type ...

Search for the Standard Model Higgs Boson in the Diphoton Decay Channel with4.9  fb−1ofppCollision Data ats=7  TeVwith ATLAS

A search for the standard model Higgs boson is performed in the diphoton decay channel. The data used correspond to an integrated luminosity of 4.9  fb-1 collected with the ATLAS detector at the Large Hadron Collider in proton-proton collisions at a center-of-mass energy of √s=7  TeV. In the diphoton mass range 110–150 GeV, the largest excess with respect to the background-only hypothesis is observed at 126.5 GeV, with a local significance of 2.8 standard deviations. Taking the look-elsewhere effect into account in the range 110–150 GeV, this significance becomes 1.5 standard deviations. The standard model Higgs boson is excluded at 95% confidence level in the mass ranges of 113–115 GeV and…

Measurement of light-by-light scattering and search for axion-like particles with 2.2 nb−1 of Pb+Pb data with the ATLAS detector

We thank CERN for the very successful operation of the LHC, as well as the support staff from our institutions without whom ATLAS could not be operated efficiently. We acknowledge the support of ANPCyT, Argentina; YerPhI, Armenia; ARC, Australia; BMWFW and FWF, Austria; ANAS, Azerbaijan; SSTC, Belarus; CNPq and FAPESP, Brazil; NSERC, NRC and CFI, Canada; CERN; ANID, Chile; CAS, MOST and NSFC, China; COLCIENCIAS, Colombia; MSMT CR, MPO CR and VSC CR, Czech Republic; DNRF and DNSRC, Denmark; IN2P3-CNRS and CEA-DRF/IRFU, France; SRNSFG, Georgia; BMBF, HGF and MPG, Germany; GSRT, Greece; RGC and Hong Kong SAR, China; ISF and Benoziyo Center, Israel; INFN, Italy; MEXT and JSPS, Japan; CNRST, Mor…

Measurement of W ± Z production in proton-proton collisions at √s =7 TeV with the ATLAS detector

A study of W±Z production in proton-proton collisions at √s=7 TeV is presented using data corresponding to an integrated luminosity of 4.6 fb−1 collected with the ATLAS detector at the Large Hadron Collider in 2011. In total, 317 candidates, with a background expectation of 68±10 events, are observed in double-leptonic decay final states with electrons, muons and missing transverse momentum. The total cross-section is determined to be σtotWZ=19.0+1.4−1.3(stat.)±0.9(syst.)±0.4(lumi.) pb, consistent with the Standard Model expectation of 17.6+1.1−1.0 pb. Limits on anomalous triple gauge boson couplings are derived using the transverse momentum spectrum of Z bosons in the selected events. The …

Search for long-lived, multi-charged particles in pp collisions at s=7 TeV using the ATLAS detector

A search for highly ionising, penetrating particles with electric charges from |q| = 2e to 6e is performed using the ATLAS detector at the CERN Large Hadron Collider. Proton-proton collision data taken at sqrt(s)=7 TeV during the 2011 running period, corresponding to an integrated luminosity of 4.4 fb^-1, are analysed. No signal candidates are observed, and 95% confidence level cross-section upper limits are interpreted as mass-exclusion lower limits for a simplified Drell--Yan production model. In this model, masses are excluded from 50 GeV up to 430, 480, 490, 470 and 420 GeV for charges 2e, 3e, 4e, 5e and 6e, respectively.

Correlation measurements in Z→τ+τ− and the τ neutrino helicity

Using data collected with the ALEPH detector at LEP correlations between the decay products of the τ+ and τ- produced in the decay of the Z have been measured. The measurements performed in the decays τ-->πν and τ-->ϱν place limits on deviations from the Standard Model. These are given by the parameter ζ with ζ = -1 for the Standard Model. The measured values are ζπ = -0.95 +/- 0.11 +/- 0.05 and ζϱ = -1.03 +/- 0.11 +/- 0.05. For models which predict ζπ = ζϱ = ζ - interpreted as the average τ neutrino helicity - the measurement is ζ = -0.99 +/- 0.07 +/- 0.04.

Search for diphoton events with large missing transverse momentum in 7 TeV proton-proton collision data with the ATLAS detector

A search for diphoton events with large missing transverse momentum has been performed using proton–proton collision data at √s = 7 TeV recorded with the ATLAS detector, corresponding to an integrated luminosity of 4.8 fb[superscript −1]. No excess of events was observed above the Standard Model prediction and model-dependent 95% confidence level exclusion limits are set. In the context of a generalised model of gauge-mediated supersymmetry breaking with a bino-like lightest neutralino of mass above 50 GeV, gluinos (squarks) below 1.07 TeV (0.87 TeV) are excluded, while a breaking scale Λ below 196 TeV is excluded for a minimal model of gauge-mediated supersymmetry breaking. For a specific …

Measurement of the production of neighbouring jets in lead–lead collisions at sNN=2.76 TeV with the ATLAS detector

This Letter presents measurements of correlated production of nearby jets in Pb+Pb collisions at root s(NN) = 2.76 TeV using the ATLAS detector at the Large Hadron Collider. The measurement was performed using 0.14 nb(-1)of data recorded in 2011. The production of correlated jet pairs was quantified using the rate, R-Delta R, of "neighbouring" jets that accompany "test" jets within a given range of angular distance, Delta R, in the pseudorapidity-azimuthal angle plane. The jets were measured in the ATLAS calorimeter and were reconstructed using the anti-ktalgorithm with radius parameters d = 0.2, 0.3, and 0.4. R-Delta R was measured in different Pb+Pbcollision centrality bins, characterized…

Measurement of Wγ and Zγ production cross sections in pp collisions at s=7 TeV and limits on anomalous triple gauge couplings with the ATLAS detector

This Letter presents measurements of l(+/-) nu gamma and l(+)l(-)gamma (l = e.mu) production in 1.02 fb(-1) of pp collision data recorded at root s = 7 TeV with the ATLAS detector at the LHC in the ...

Search for long-lived stoppedR-hadrons decaying out of time withppcollisions using the ATLAS detector

An updated search is performed for gluino, top squark, or bottom squark R-hadrons that have come to rest within the ATLAS calorimeter, and decay at some later time to hadronic jets and a neutralino, using 5.0 and 22.9 fb(-1) of pp collisions at 7 and 8 TeV, respectively. Candidate decay events are triggered in selected empty bunch crossings of the LHC in order to remove pp collision backgrounds. Selections based on jet shape and muon system activity are applied to discriminate signal events from cosmic ray and beam-halo muon backgrounds. In the absence of an excess of events, improved limits are set on gluino, stop, and sbottom masses for different decays, lifetimes, and neutralino masses. …

Performance of $b$-Jet Identification in the ATLAS Experiment

We thank CERN for the very successful operation of the LHC, as well as the support staff from our institutions without whom ATLAS could not be operated efficiently. We acknowledge the support of ANPCyT, Argentina; YerPhI, Armenia; ARC, Australia; BMWFW and FWF, Austria; ANAS, Azerbaijan; SSTC, Belarus; CNPq and FAPESP, Brazil; NSERC, NRC and CFI, Canada; CERN; CONICYT, Chile; CAS, MOST and NSFC, China; COLCIENCIAS, Colombia; MSMT CR, MPO CR and VSC CR, Czech Republic; DNRF, DNSRC and Lundbeck Foundation, Denmark; IN2P3-CNRS, CEA-DSM/IRFU, France; GNSF, Georgia; BMBF, HGF, and MPG, Germany; GSRT, Greece; RGC, Hong Kong SAR, China; ISF, I-CORE and Benoziyo Center, Israel; INFN, Italy; MEXT an…

Measurement of Dijet Azimuthal Decorrelations inppCollisions ats=7  TeV

Azimuthal decorrelations between the two central jets with the largest transverse momenta are sensitive to the dynamics of events with multiple jets. We present a measurement of the normalized differential cross section based on the full data set ( integral Ldt = 36 pb(-1)) acquired by the ATLAS detector during the 2010 root s = 7 TeV proton-proton run of the LHC. The measured distributions include jets with transverse momenta up to 1.3 TeV, probing perturbative QCD in a high-energy regime.

Measurement of prompt photon production in sNN=8.16 TeV p + Pb collisions with ATLAS

The inclusive production rates of isolated, prompt photons in p+Pb collisions at sNN=8.16 TeV are studied with the ATLAS detector at the Large Hadron Collider using a dataset with an integrated luminosity of 165 nb −1 recorded in 2016. The cross-section and nuclear modification factor RpPb are measured as a function of photon transverse energy from 20 GeV to 550 GeV and in three nucleon–nucleon centre-of-mass pseudorapidity regions, (−2.83,−2.02) , (−1.84,0.91) , and (1.09,1.90) . The cross-section and RpPb values are compared with the results of a next-to-leading-order perturbative QCD calculation, with and without nuclear parton distribution function modifications, and with expectations b…

Measurement of the WW cross section in s=7 TeV pp collisions with the ATLAS detector and limits on anomalous gauge couplings

This Letter reports a measurement of the W W production cross section in root s = 7 TeV pp collisions using data corresponding to an integrated luminosity of 1.02 fb(-1) collected with the ATLAS de ...

Search for excited electrons and muons in root s=8 TeV proton-proton collisions with the ATLAS detector

The ATLAS detector at the Large Hadron Collider is used to search for excited electrons and excited muons in the channel pp → ℓℓ* → ℓℓγ, assuming that excited leptons are produced via contact interactions. The analysis is based on 13 fb[superscript −1] of pp collisions at a centre-of-mass energy of 8 TeV. No evidence for excited leptons is found, and a limit is set at the 95% credibility level on the cross section times branching ratio as a function of the excited-lepton mass m[subscript ℓ*]. For m[subscript ℓ*] ≥ 0.8 TeV, the respective upper limits on σB(ℓ* → ℓγ) are 0.75 and 0.90 fb for the e* and μ* searches. Limits on σB are converted into lower bounds on the compositeness scale Λ. In …

Search for single top production in e+e− collisions at –202 GeV

Abstract Single top production via flavour changing neutral currents in the reactions e + e − → t c / u is searched for in approximately 411 pb −1 of data collected by ALEPH at centre-of-mass energies in the range between 189 and 202 GeV. In total, 58 events are selected in the data to be compared with 50.3 expected from Standard Model backgrounds. No deviation from the Standard Model expectation is observed. Upper limits at 95% CL on single top production cross sections at s =189 –202 GeV are derived. A model-dependent limit on the sum of branching ratios BR(t→Zc)+BR(t→Zu)

Search for a heavy Standard Model Higgs boson in the channel H→ZZ→ℓ+ℓ−qq¯ using the ATLAS detector

A search for a heavy Standard Model Higgs boson decaying via H -> ZZ -> l(+)l(-)q (q) over bar, where l = e, mu, is presented. The search is performed using a data set of pp collisions at root s = 7 TeV, corresponding to an integrated luminosity of 1.04 fb(-1) collected in 2011 by the ATLAS detector at the CERN LHC collider. No significant excess of events above the estimated background is found. Upper limits at 95% confidence level on the production cross section (relative to that expected from the Standard Model) of a Higgs boson with a mass in the range between 200 and 600 GeV are derived. Within this mass range, there is at present insufficient sensitivity to exclude a Standard Model Hi…

Measurements of the electron and muon inclusive cross-sections in proton–proton collisions at s=7 TeV with the ATLAS detector

This Letter presents measurements of the differential cross-sections for inclusive electron and muon production in proton-proton collisions at a centre-of-mass energy of root s = 7 TeV, using data collected by the ATLAS detector at the LHC. The muon cross-section is measured as a function of p(T) in the range 4 < p(T) < 100 GeV and within pseudorapidity vertical bar eta vertical bar < 2.5. In addition the electron and muon cross-sections are measured in the range 7 < p(T) < 26 GeV and within vertical bar eta vertical bar < 2.0, excluding 1.37 < vertical bar eta vertical bar < 1.52. Integrated luminosities of 1.3 pb(-1) and 1.4 pb(-1) are used for the electron and muon measurements, respecti…

A measurement of the gluon splitting rate into bb̄ pairs in hadronic Z decays

Abstract A measurement of the fraction of hadronic Z decays in which a gluon splits into a b b pair, g b b , is presented using data collected by ALEPH from 1992 to 1995 at the Z resonance. The selection is based on four-jet events. Events are selected by means of topological cuts and a lifetime tag. The result is g b b =(2.77±0.42 (stat)±0.57 (syst))×10 −3 .

Measurement of the top quark-pair production cross section with ATLAS in pp collisions at $\sqrt{s}=7$  TeV

A measurement of the production cross-section for top quark pairs($\ttbar$) in $pp$ collisions at $\sqrt{s}=7 \TeV$ is presented using data recorded with the ATLAS detector at the Large Hadron Collider. Events are selected in two different topologies: single lepton (electron $e$ or muon $\mu$) with large missing transverse energy and at least four jets, and dilepton ($ee$, $\mu\mu$ or $e\mu$) with large missing transverse energy and at least two jets. In a data sample of 2.9 pb-1, 37 candidate events are observed in the single-lepton topology and 9 events in the dilepton topology. The corresponding expected backgrounds from non-$\ttbar$ Standard Model processes are estimated using data-driv…

Measurement of multi-jet cross sections in proton-proton collisions at a 7 TeV center-of-mass energy

Inclusive multi-jet production is studied in proton–proton collisions at a center-of-mass energy of 7 TeV, using the ATLAS detector. The data sample corresponds to an integrated luminosity of 2.4 pb−1. Results on multi-jet cross sections are presented and compared to both leading-order plus parton-shower Monte Carlo predictions and to next-to-leading-order QCD calculations.

Search for supersymmetry in pp collisions at s=7 TeV in final states with missing transverse momentum and b-jets

Results are presented of a search for supersymmetric particles in events with large missing transverse momentum and at least one heavy flavour jet candidate in sqrt{s} = 7 TeV proton-proton collisions. In a data sample corresponding to an integrated luminosity of 35 pb-1 recorded by the ATLAS experiment at the Large Hadron Collider, no significant excess is observed with respect to the prediction for Standard Model processes. For R-parity conserving models in which sbottoms (stops) are the only squarks to appear in the gluino decay cascade, gluino masses below 590 GeV (520 GeV) are excluded at the 95% C.L. The results are also interpreted in an MSUGRA/CMSSM supersymmetry breaking scenario w…

Measurement of the production cross section for a Higgs boson in association with a vector boson in the H → WW⁎ → ℓνℓν channel in pp collisions at s=13 TeV with the ATLAS detector

A measurement of the Higgs boson production cross sections via associated WH and ZH production using H -> WW* -> l nu l nu decays, where l stands for either an electron or a muon, is presente ...

A search for t[bar over t] resonances in lepton+jets events with highly boosted top quarks collected in pp collisions at √s = 7 TeV with the ATLAS detector

A search for resonant production of high-mass top-quark pairs is performed on 2.05 fb[superscript −1] of proton-proton collisions at √s = 7 TeV collected in 2011 with the ATLAS experiment at the Large Hadron Collider. This analysis of the lepton+jets final state is specifically designed for the particular topology that arises from the decay of highly boosted top quarks. The observed t[bar over t] invariant mass spectrum is found to be compatible with the Standard Model prediction and 95% credibility level upper limits are derived on the t[bar over t] production rate through new massive states. An upper limit of 0.7 pb is set on the production cross section times branching fraction of a narr…

Production of Ds** mesons in hadronic Z decays

The production rates of the orbitally excited Ds** mesons, Ds1 and Ds2*, are measured with the 4.1 million hadronic Z decays recorded by the ALEPH detector during 1991--1995. The Ds** mesons are reconstructed in the decay modes Ds1+ -&gt; D*+ K0, Ds1+ -&gt; D*0 K+ and Ds2*+ -&gt; D0 K+. The production rate of the Ds1 is measured to be n(Z-&gt;Ds1+-)=(0.52+-0.09+-0.06)%, under the assumption that the two considered decay modes of the Ds1 saturate the branching ratio. The production rate of the Ds2* is determined to be n(Z-&gt;Ds2*+-)=(0.83+-0.29+0.07-0.13)%, assuming that the branching fraction of the decay Ds2*+ -&gt; D0 K+ is 45%. The production rates in Z-&gt;cc and Z-&gt;bbar decays are …

Search for supersymmetry with jets, missing transverse momentum and at least one hadronically decaying τ lepton in proton–proton collisions at s=7 TeV with the ATLAS detector

A search for production of supersymmetric particles in final states containing jets, missing transverse momentum, and at least one hadronically decaying tau lepton is presented. The data were recor ...

Search for microscopic black holes in a like-sign dimuon final state using large track multiplicity with the ATLAS detector

A search is presented for microscopic black holes in a like-sign dimuon final state in proton-proton collisions at √s= 8 TeV. The data were collected with the ATLAS detector at the Large Hadron Collider in 2012 and correspond to an integrated luminosity of 20.3 fb-1. Using a high track multiplicity requirement, 0.6±0.2 background events from Standard Model processes are predicted and none observed. This result is interpreted in the context of low-scale gravity models and 95% CL lower limits on microscopic black hole masses are set for different model assumptions.

Search for single b⁎-quark production with the ATLAS detector at s=7 TeV

The results of a search for an excited bottom-quark b* in pp collisions at root s = 7 TeV, using 4.7 fb(-1) of data collected by the ATLAS detector at the LHC are presented. In the model studied, a ...

Transverse momentum, rapidity, and centrality dependence of inclusive charged-particle production in sNN=5.02 TeV p+ Pb collisions measured by the ATLAS experiment

Measurements of the per-event charged-particle yield as a function of the charged-particle transverse momentum and rapidity are performed using p+Pbp+Pb collision data collected by the ATLAS experiment at the LHC at a centre-of-mass energy of sqrt (SNN) = 5.01 TeV. Charged particles are reconstructed over pseudorapidity |η|<2.3|η|<2.3 and transverse momentum between 0.1 GeV0.1 GeV and 22 GeV22 GeV in a dataset corresponding to an integrated luminosity of 1 μb−11 μb−1. The results are presented in the form of charged-particle nuclear modification factors, where the p+Pbp+Pb charged-particle multiplicities are compared between central and peripheral p+Pbp+Pb collisions as well as to charged-p…

Bose-Einstein correlations in W-pair decays

Bose-Einstein correlations are studied in semileptonic (WW --> q (q) over bar lv) and fully hadronic (WW --> q (q) over bar q (q) over bar) W-pair decays with the ALEPH detector at LEP at centre-of-mass energies of 172, 183 and 189 GeV. They are compared with those made at the Z peak after correction for the different flavour compositions. A Monte Carlo model of Bose-Einstein correlations based on the JETSET hadronization scheme was tuned to the Z data and reproduces the correlations in the WW --> q (q) over bar lv events. The same Monte Carlo reproduces the correlations in the WW --> q (q) over bar q (q) over bar channel assuming independent fragmentation of the two W's. A variant of this …

Measurement of underlying event characteristics using charged particles inppcollisions ats=900  GeVand 7 TeV with the ATLAS detector

Measurements of charged particle distributions, sensitive to the underlying event, have been performed with the ATLAS detector at the LHC. The measurements are based on data collected using a minimum-bias trigger to select proton-proton collisions at center-of-mass energies of 900 GeV and 7 TeV. The "underlying event" is defined as those aspects of a hadronic interaction attributed not to the hard scattering process, but rather to the accompanying interactions of the rest of the proton. Three regions are defined in azimuthal angle with respect to the highest transverse momentum charged particle in the event, such that the region transverse to the dominant momentum-flow is most sensitive to …

Search for a Heavy Particle Decaying into an Electron and a Muon with the ATLAS Detector ins=7  TeVppcollisions at the LHC

This Letter presents the first search for a heavy particle decaying into an e(+/-)mu(-/+) final state in root s = 7 TeV pp collisions at the LHC. The data were recorded by the ATLAS detector during 2010 and correspond to a total integrated luminosity of 35 pb(-1). No excess above the standard model background expectation is observed. Exclusions at 95% confidence level are placed on two representative models. In an R-parity violating supersymmetric model, tau sneutrinos with a mass below 0.75 TeV are excluded, assuming all R-parity violating couplings are zero except lambda(311)' = 0.11 and lambda(312) = 0.07. In a lepton flavor violating model, a Z'-like vector boson with masses of 0.70-1.0…

Search for contact interactions in dilepton events from pp collisions at s=7 TeV with the ATLAS detector

This Letter presents a search for contact interactions in the dielectron and dimuon channels using data from proton-proton collisions produced by the LHC at,root s = 7 TeV and recorded by the ATLAS ...

Measurement with the ATLAS detector of multi-particle azimuthal correlations in p+Pb collisions at sNN=5.02 TeV

In order to study further the long-range correlations ("ridge") observed recently in p + Pb collisions at root s(NN) = 5.02 TeV, the second-order azimuthal anisotropy parameter ofcharged particles, ...

Search for low-mass resonances decaying into two jets and produced in association with a photon using pp collisions at s=13 TeV with the ATLAS detector

A search is performed for localised excesses in dijet mass distributions of low-dijet-mass events produced in association with a high transverse energy photon. The search uses up to 79.8 fb−1 of LHC proton–proton collisions collected by the ATLAS experiment at a centre-of-mass energy of 13 TeV during 2015–2017. Two variants are presented: one which makes no jet flavour requirements and one which requires both jets to be tagged as b-jets. The observed mass distributions are consistent with multi-jet processes in the Standard Model. The data are used to set upper limits on the production cross-section for a benchmark Z′ model and, separately, on generic Gaussian-shape contributions to the mas…

Leptonic decays of the D-s meson

The purely leptonic decays Ds -&gt; tau nu and Ds -&gt; mu nu are studied in a sample of four million hadronic Z decays collected with the ALEPH detector at the LEP e+e- collider from 1991 to 1995. The branching fractions are extracted from a combination of two analyses, one optimized to select Ds -&gt; tau nu decays with tau -&gt; e nu nubar or mu nu nubar, and the other optimized for Ds-&gt; mu nu decays. The results are used to evaluate the Ds decay constant, within the Standard Model: fDs = [285 +- 19(stat) +- 40 (syst)] MeV

Search for diphoton events with large missing transverse energy in 7 TeV proton-proton collisions with the ATLAS detector.

A search for diphoton events with large missing transverse energy is presented. The data were collected with the ATLAS detector in proton-proton collisions at √s=7  TeV at the CERN Large Hadron Collider and correspond to an integrated luminosity of 3.1  pb−1. No excess of such events is observed above the standard model background prediction. In the context of a specific model with one universal extra dimension with compactification radius R and gravity-induced decays, values of 1/R<729  GeV are excluded at 95% C. L., providing the most sensitive limit on this model to date.

Search for new phenomena in final states with large jet multiplicities and missing transverse momentum at s√=8 TeV proton-proton collisions using the ATLAS experiment

A search is presented for new particles decaying to large numbers (7 or more) of jets, with missing transverse momentum and no isolated electrons or muons. This analysis uses 20.3 fb[superscript −1] of pp collision data at s√ = 8 TeV collected by the ATLAS experiment at the Large Hadron Collider. The sensitivity of the search is enhanced by considering the number of b-tagged jets and the scalar sum of masses of large-radius jets in an event. No evidence is found for physics beyond the Standard Model. The results are interpreted in the context of various simplified supersymmetry-inspired models where gluinos are pair produced, as well as an mSUGRA/CMSSM model.

Measurement of the inelastic proton-proton cross-section at √s = 7 TeV with the ATLAS detector

The dependence of the rate of proton–proton interactions on the centre-of-mass collision energy, √s, is of fundamental importance for both hadron collider physics and particle astrophysics. The dependence cannot yet be calculated from first principles; therefore, experimental measurements are needed. Here we present the first measurement of the inelastic proton–proton interaction cross-section at a centre-of-mass energy, √s, of 7 TeV using the ATLAS detector at the Large Hadron Collider. Events are selected by requiring hits on scintillation counters mounted in the forward region of the detector. An inelastic cross-section of 60.3±2.1 mb is measured for ξ>5×10[superscript −6], where ξ is ca…

Inclusive semileptonic branching ratios of b hadrons produced in Z decays

A measurement of the inclusive semileptonic branching ratios of b hadrons produced in Z decay is presented, using four million hadronic events collected by the ALEPH detector from 1991 to 1995. Electrons and muons are selected opposite to b-tagged hemispheres. Two different methods are explored to distinguish the contributions from direct $\bl$ and cascade $\bcl$ decays to the total lepton yield. One is based on the lepton transverse momentum spectrum, the other makes use of the correlation between the charge of the lepton and charge estimators built from tracks in the opposite hemisphere of the event. The latter method reduces the dependence on the modelling of semileptonic b decays. The r…

A measurement of the ratio of the W and Z cross sections with exactly one associated jet in pp collisions at with ATLAS

The ratio of production cross sections of the W and Z bosons with exactly one associated jet is presented as a function of jet transverse momentum threshold. The measurement has been designed to ma ...

Study of the material of the ATLAS inner detector for Run 2 of the LHC

The ATLAS inner detector comprises three different sub-detectors: the pixel detector, the silicon strip tracker, and the transition-radiation drift-tube tracker. The Insertable B-Layer, a new innermost pixel layer, was installed during the shutdown period in 2014, together with modifications to the layout of the cables and support structures of the existing pixel detector. The material in the inner detector is studied with several methods, using a low-luminosity root s = 13 TeV pp collision sample corresponding to around 2.0 nb(-1) collected in 2015 with the ATLAS experiment at the LHC. In this paper, the material within the innermost barrel region is studied using reconstructed hadronic in…

Search for pair production of heavy top-like quarks decaying to a high-pT W boson and a b quark in the lepton plus jets final state at s=7 TeV with the ATLAS detector

A search is presented for production of a heavy up-type quark (t') together with its antiparticle, assuming a significant branching ratio for subsequent decay into a W boson and a b quark. The search is based on 4.7 fb(-1) of pp collisions root s = 7 TeV recorded in 2011 with the ATLAS detector at the CERN Large Hadron Collider. Data are analyzed in the lepton + jets final state, characterized by a high-transverse-momentum isolated electron or muon, large missing transverse momentum and at least three jets. The analysis strategy relies on the substantial boost of the W bosons in the t'(t') over bar signal when m(t') greater than or similar to 400 GeV. No significant excess of events above t…

Determination of A(FB)(b) using jet charge measurements in Z decays

An improved measurement of the forward-backward asymmetry in Z --> b (b) over bar decays is presented, based on a sample of 4.1 million hadronic Z decays collected by ALEPH between 1991 and 1995. Data are analysed as a function of polar angle of the event axis and b purity. The event tagging efficiency and mean b-jet hemisphere charge are measured directly from data. From the measured forward-backward jet charge asymmetry, the b quark asymmetry at root s= m(Z) is determined to be: A(FB)(b) = 0.1017 +/- 0.0032(syst.) +/- 0.0032(syst.). In the context of the Standard Model this corresponds to a value of the effective weak mixing angle of sin(2) theta(W)(eff)= 0.23109 +/- 0.00096. (C) 1998 Pub…