0000000000028548
AUTHOR
Y. Zhou
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 ...
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.…
Observation of light-by-light scattering in ultraperipheral Pb+Pb collisions with the ATLAS detector
This Letter describes the observation of the light-by-light scattering process, γγ→γγ, in Pb+Pb collisions at √sNN=5.02 TeV. The analysis is conducted using a data sample corresponding to an integrated luminosity of 1.73 nb−1, collected in November 2018 by the ATLAS experiment at the LHC. Light-by-light scattering candidates are selected in events with two photons produced exclusively, each with transverse energy EγT>3 GeV and pseudorapidity |ηγ|<2.4, diphoton invariant mass above 6 GeV, and small diphoton transverse momentum and acoplanarity. After applying all selection criteria, 59 candidate events are observed for a background expectation of 12±3 events. The observed excess of events…
HΛ3 and H‾Λ¯3 production in Pb–Pb collisions at sNN=2.76 TeV
Abstract The production of the hypertriton nuclei H Λ 3 and H ‾ Λ ¯ 3 has been measured for the first time in Pb–Pb collisions at s NN = 2.76 TeV with the ALICE experiment at LHC. The p T -integrated H Λ 3 yield in one unity of rapidity, d N / d y × B . R . ( H Λ 3 → He 3 , π − ) = ( 3.86 ± 0.77 ( stat. ) ± 0.68 ( syst. ) ) × 10 − 5 in the 0–10% most central collisions, is consistent with the predictions from a statistical thermal model using the same temperature as for the light hadrons. The coalescence parameter B 3 shows a dependence on the transverse momentum, similar to the B 2 of deuterons and the B 3 of 3He nuclei. The ratio of yields S 3 = H Λ 3 / ( He 3 × Λ / p ) was measured to b…
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…
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…
Search for New Phenomena intt¯Events with Large Missing Transverse Momentum in Proton-Proton Collisions ats=7 TeVwith the ATLAS Detector
A search for new phenomena in tt events with large missing transverse momentum in proton-proton collisions at a center-of-mass energy of 7 TeV is presented. The measurement is based on 1.04 fb-1 of data collected with the ATLAS detector at the LHC. Contributions to this final state may arise from a number of standard model extensions. The results are interpreted in terms of a model where new top-quark partners are pair produced and each decay to an on-shell top (or antitop) quark and a long-lived undetected neutral particle. The data are found to be consistent with standard model expectations. A limit at 95% confidence level is set excluding a cross section times branching ratio of 1.1 pb …
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…
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…
Freeze-out radii extracted from three-pion cumulants in pp, p–Pb and Pb–Pb collisions at the LHC
In high-energy collisions, the spatio-temporal size of the particle production region can be measured using the Bose-Einstein correlations of identical bosons at low relative momentum. The source radii are typically extracted using two-pion correlations, and characterize the system at the last stage of interaction, called kinetic freeze-out. In low-multiplicity collisions, unlike in high-multiplicity collisions, two-pion correlations are substantially altered by background correlations, e.g. mini-jets. Such correlations can be suppressed using three-pion cumulant correlations. We present the first measurements of the size of the system at freeze-out extracted from three-pion cumulant correl…
Transverse momentum spectra and nuclear modification factors of charged particles in pp, p-Pb and Pb-Pb collisions at the LHC
We report the measured transverse momentum ($p_{\rm T}$) spectra of primary charged particles from pp, p-Pb and Pb-Pb collisions at a center-of-mass energy $\sqrt{s_{\rm NN}} = 5.02$ TeV in the kinematic range of $0.15<p_{\rm T}<50$ GeV/$c$ and $|\eta|< 0.8$. A significant improvement of systematic uncertainties motivated the reanalysis of data in pp and Pb-Pb collisions at $\sqrt{s_{\rm NN}} = 2.76$ TeV, as well as in p-Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV, which is also presented. Spectra from Pb-Pb collisions are presented in nine centrality intervals and are compared to a reference spectrum from pp collisions scaled by the number of binary nucleon-nucleon collisions. For cent…
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 …
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…
Dielectron and heavy-quark production in inelastic and high-multiplicity proton–proton collisions at s=13TeV
The measurement of dielectron production is presented as a function of invariant mass and transverse momentum (pT) at midrapidity (|ye|<0.8) in proton–proton (pp) collisions at a centre-of-mass energy of s=13 TeV. The contributions from light-hadron decays are calculated from their measured cross sections in pp collisions at s=7 TeV or 13 TeV. The remaining continuum stems from correlated semileptonic decays of heavy-flavour hadrons. Fitting the data with templates from two different MC event generators, PYTHIA and POWHEG, the charm and beauty cross sections at midrapidity are extracted for the first time at this collision energy: dσcc¯/dy|y=0=974±138(stat.)±140(syst.)±214(BR)μb and dσbb…
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…
Charged jet cross section and fragmentation in proton-proton collisions at √s = 7 TeV
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. We report the differential charged jet cross section and jet fragmentation distributions measured with the ALICE detector in proton-proton collisions at a center-of-mass energy √s=7 TeV. Jets with pseudorapidity |η|40 GeV/c, the pythia calculations also agree with the measured charged jet cross section. pythia6 simulations describe the fragmentation distributions to 15%. Larger discrepancies are observed for pythia8. SCOAP
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 ...
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…
Measurement of the transverse momentum distribution ofWbosons inppcollisions ats=7 TeVwith the ATLAS detector
This paper describes a measurement of the W boson transverse momentum distribution using ATLAS pp collision data from the 2010 run of the LHC at root s = 7 TeV, corresponding to an integrated lumin ...
S-wave KK* interactions in a finite volume and the f(1)(1285)
International audience; Lattice QCD simulations provide a promising way to disentangle different interpretations of hadronic resonances, which might be of particular relevance to understand the nature of the so-called XYZ particles. Recent studies have shown that in addition to the well-established naive quark model picture, the axial-vector meson f1(1285) can also be understood as a dynamically generated state built upon the KK∗ interaction. In this work, we calculate the energy levels of the KK∗ system in the f1(1285) channel in finite volume using the chiral unitary approach. We propose to calculate the loop function in the dimensional regularization scheme, which is equivalent to the hy…
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.
Search for the neutral Higgs bosons of the Minimal Supersymmetric Standard Model in $pp$ collisions at $\sqrt{s}=7$ TeV with the ATLAS detector
A search for neutral Higgs bosons of the Minimal Supersymmetric Standard Model (MSSM) is reported. The analysis is based on a sample of proton-proton collisions at a centre-of-mass energy of 7 TeV recorded with the ATLAS detector at the Large Hadron Collider. The data were recorded in 2011 and correspond to an integrated luminosity of 4.7 fb[superscript −1] to 4.8 fb[superscript −1]. Higgs boson decays into oppositely-charged muon or τ lepton pairs are considered for final states requiring either the presence or absence of b-jets. No statistically significant excess over the expected background is observed and exclusion limits at the 95% confidence level are derived. The exclusion limits ar…
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…
Measurements ofWγandZγproduction inppcollisions ats=7 TeVwith the ATLAS detector at the LHC
The integrated and differential fiducial cross sections for the production of a W or Z boson in association with a high-energy photon are measured using pp collisions at root s = 7 TeV. The analyse ...
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 ...
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 ...
Search for Dilepton Resonances inppCollisions ats=7 TeVwith the ATLAS Detector
This Letter reports on a search for narrow high-mass resonances decaying into dilepton final states. The data were recorded by the ATLAS experiment in pp collisions at root s = 7 TeV at the Large Hadron Collider and correspond to a total integrated luminosity of 1.08 (1.21) fb(-1) in the e(+)e(-) (mu(+)mu(-)) channel. No statistically significant excess above the standard model expectation is observed and upper limits are set at the 95% C. L. on the cross section times branching fraction of Z' resonances and Randall-Sundrum gravitons decaying into dileptons as a function of the resonance mass. A lower mass limit of 1.83 TeV on the sequential standard model Z' boson is set. A Randall-Sundrum…
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…
Efficient generation of energetic ions in multi-ion plasmas by radio-frequency heating
We describe a new technique for the efficient generation of high-energy ions with electromagnetic ion cyclotron waves in multi-ion plasmas. The discussed ‘three-ion’ scenarios are especially suited for strong wave absorption by a very low number of resonant ions. To observe this effect, the plasma composition has to be properly adjusted, as prescribed by theory. We demonstrate the potential of the method on the world-largest plasma magnetic confinement device, JET (Joint European Torus, Culham, UK), and the high-magnetic-field tokamak Alcator C-Mod (Cambridge, USA). The obtained results demonstrate efficient acceleration of 3He ions to high energies in dedicated hydrogen–deuterium mixtures.…
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 ...
The ALICE Transition Radiation Detector: Construction, operation, and performance
The Transition Radiation Detector (TRD) was designed and built to enhance the capabilities of the ALICE detector at the Large Hadron Collider (LHC). While aimed at providing electron identification and triggering, the TRD also contributes significantly to the track reconstruction and calibration in the central barrel of ALICE. In this paper the design, construction, operation, and performance of this detector are discussed. A pion rejection factor of up to 410 is achieved at a momentum of 1 GeV/$c$ in p-Pb collisions and the resolution at high transverse momentum improves by about 40% when including the TRD information in track reconstruction. The triggering capability is demonstrated both …
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 …
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…
Centrality, rapidity and transverse momentum dependence of J/ψ suppression in Pb–Pb collisions at sNN=2.76 TeV
The inclusive J/.nuclear modification factor (R-AA) in Pb-Pb collisions at root(NN)-N-S = 2.76TeVhas been measured by ALICE as a function of centrality in the e+ e-decay channel at mid-rapidity (| y| < 0.8) and as a function of centrality, transverse momentum and rapidity in the + -decay channel at forward-rapidity (2.5 < y < 4). The J/.yields measured in Pb-Pb are suppressed compared to those in ppcollisions scaled by the number of binary collisions. The RAAintegrated over a centrality range corresponding to 90% of the inelastic Pb-Pb cross section is 0.72 - 0.06(stat.) - 0.10(syst.) at mid-rapidity and 0.58 - 0.01(stat.) - 0.09(syst.) at forward-rapidity. At low transverse momentum, signi…
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…
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…
Searches for transverse momentum dependent flow vector fluctuations in Pb-Pb and p-Pb collisions at the LHC
The measurement of azimuthal correlations of charged particles is presented for Pb-Pb collisions at $\sqrt{s_{\rm NN}}=$ 2.76 TeV and p-Pb collisions at $\sqrt{s_{\rm NN}}=$ 5.02 TeV with the ALICE detector at the CERN Large Hadron Collider. These correlations are measured for the second, third and fourth order flow vector in the pseudorapidity region $|��|<0.8$ as a function of centrality and transverse momentum $p_{\rm T}$ using two observables, to search for evidence of $p_{\rm T}$-dependent flow vector fluctuations. For Pb-Pb collisions at 2.76 TeV, the measurements indicate that $p_{\rm T}$-dependent fluctuations are only present for the second order flow vector. Similar results hav…
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).
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…
Novel method for determination of tritium depth profiles in metallic samples
Tritium accumulation in fusion reactor materials is considered a serious radiological issue, therefore a lot of effort has been concentrated on the development of radiometric techniques. A novel method, based on gradual dissolution, for the determination of the total tritium content and its depth profiles in metallic samples is demonstrated. This method allows for the measurement of tritium in metallic samples after their exposure to a hydrogen and tritium mixture, tritium containing plasma or after irradiation with neutrons resulting in tritium formation. In this method, successive layers of metal are removed using an appropriate etching agent in the controlled regime and the amount of evo…
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 theZZProduction Cross Section and Limits on Anomalous Neutral Triple Gauge Couplings in Proton-Proton Collisions ats=7 TeVwith the ATLAS Detector
A measurement of the ZZ production cross section in proton-proton collisions at root s = 7 TeV using data corresponding to an integrated luminosity of 1.02 fb(-1) recorded by the ATLAS experiment a ...
Harmonic decomposition of two particle angular correlations in Pb–Pb collisions at sNN=2.76 TeV
Angular correlations between unidentified charged trigger (t) and associated (a) particles are measured by the ALICE experiment in Pb-Pb collisions at root s(NN) = 2.76 TeV for transverse momenta 0.25 p(T)(a). The shapes of the pair correlation distributions are studied in a variety of collision centrality classes between 0 and 50% of the total hadronic cross section for particles in the pseudorapidity interval |eta| 0.8, and are referred to as "long-range correlations". Fourier components V-n Delta equivalent to are extracted from the long-range azimuthal correlation functions. If particle pairs are correlated to one another through their individual correlation to a common symmetry plane, …
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 ...
Inclusive quarkonium production at forward rapidity in pp collisions at \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\mathbf {\sqrt{s}=8}~$$\end{document}s=8TeV
We report on the inclusive production cross sections of \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\mathrm{J}/\psi }$$\end{document}J/ψ, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\psi (\mathrm{2S})}$$\end{document}ψ(2S), \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepac…
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…
First measurement of the |t|-dependence of coherent J/ψ photonuclear production
The first measurement of the dependence on $|t|$, the square of the momentum transferred between the incoming and outgoing target nucleus, of coherent J/ψ photoproduction is presented. The data were measured with the ALICE detector in ultra-peripheral Pb-Pb collisions at a centre-of-mass energy per nucleon pair $\sqrt{s_{\rm NN}} = 5.02$ TeV with the J/$\psi$ produced in the central rapidity region $|y| < 0.8$, which corresponds to the small Bjorken-$x$ range $(0.3 − 1.4) \times 10 ^{−3}$. The measured $|t|$-dependence is not described by computations based only on the Pb nuclear form factor, while the photonuclear cross section is better reproduced by models including shadowing according t…
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…
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, …
Search for new phenomena in final states with large jet multiplicities and missing transverse momentum using root s=7 TeV pp collisions with the ATLAS detector
Results are presented of a search for any particle(s) decaying to six or more jets in association with missing transverse momentum. The search is performed using 1.34fb−1 of s √ s = 7 TeV proton-proton collisions recorded by the ATLAS detector during 2011. Data-driven techniques are used to determine the backgrounds in kinematic regions that require at least six, seven or eight jets, well beyond the multiplicities required in previous analyses. No evidence is found for physics beyond the Standard Model. The results are interpreted in the context of a supersymmetry model (MSUGRA/CMSSM) where they extend previous constraints.
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 WH production with a light Higgs boson decaying to prompt electron-jets in proton–proton collisions at \(\sqrt {s}=7\) TeV with the ATLAS detector
A search is performed for WH production with a light Higgs boson decaying to hidden-sector particles resulting in clusters of collimated electrons, known as electron-jets. The search is performed with 2.04 fb[superscript −1] of data collected in 2011 with the ATLAS detector at the Large Hadron Collider in proton–proton collisions at √s=7 TeV . One event satisfying the signal selection criteria is observed, which is consistent with the expected background rate. Limits on the product of the WH production cross section and the branching ratio of a Higgs boson decaying to prompt electron-jets are calculated as a function of a Higgs boson mass in the range from 100 to 140 GeV.
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.
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…
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.
Real-time data processing in the ALICE High Level Trigger at the LHC
At the Large Hadron Collider at CERN in Geneva, Switzerland, atomic nuclei are collided at ultra-relativistic energies. Many final-state particles are produced in each collision and their properties are measured by the ALICE detector. The detector signals induced by the produced particles are digitized leading to data rates that are in excess of 48 GB/$s$. The ALICE High Level Trigger (HLT) system pioneered the use of FPGA- and GPU-based algorithms to reconstruct charged-particle trajectories and reduce the data size in real time. The results of the reconstruction of the collision events, available online, are used for high level data quality and detector-performance monitoring and real-tim…
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…
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…
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 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 <= pT < 430 GeV and |y| < 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…
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…
Search for a common baryon source in high-multiplicity pp collisions at the LHC
Physics letters / B B811, 135849 (2020). doi:10.1016/j.physletb.2020.135849
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…
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 displaced muonic lepton jets from light Higgs boson decay in proton–proton collisions at s=7 TeV with the ATLAS detector
A search is performed for collimated muon pairs displaced from the primary vertex produced in the decay of long-lived neutral particles in proton-proton collisions at root s = 7 TeV centre-of-mass ...
Charged jet cross sections and properties in proton-proton collisions at $\sqrt{s}=7$ TeV
The differential charged jet cross sections, jet fragmentation distributions, and jet shapes are measured in minimum bias proton-proton collisions at centre-of-mass energy $\sqrt{s}=7$ TeV using the ALICE detector at the LHC. Jets are reconstructed from charged particle momenta in the mid-rapidity region using the sequential recombination $k_{\rm T}$ and anti-$k_{\rm T}$ as well as the SISCone jet finding algorithms with several resolution parameters in the range $R=0.2$ to $0.6$. Differential jet production cross sections measured with the three jet finders are in agreement in the transverse momentum ($p_{\rm T}$) interval $20<p_{\rm T}^{\rm jet,ch}<100$ GeV/$c$. They are also consistent w…
Comparison of the structure of the plasma-facing surface and tritium accumulation in beryllium tiles from JET ILW campaigns 2011-2012 and 2013-2014
In this study, beryllium tiles from Joint European Torus (JET) vacuum vessel wall were analysed and compared regarding their position in the vacuum vessel and differences in the exploitation conditions during two campaigns of ITER-Like-Wall (ILW) in 2011-2012 (ILW1) and 2013-2014 (ILW2) Tritium content in beryllium samples were assessed. Two methods were used to measure tritium content in the samples - dissolution under controlled conditions and tritium thermal desorption. Prior to desorption and dissolution experiments, scanning electron microscopy and energy dispersive x-ray spectroscopy were used to study structure and chemical composition of plasma-facing-surfaces of the beryllium sampl…
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…
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…
Dielectron production in proton-proton and proton-lead collisions at √sNN=5.02TeV
The first measurements of dielectron production at midrapidity (|ηe| < 0.8) in proton–proton and proton–lead collisions at √sNN = 5.02 TeV at the LHC are presented. The dielectron cross section is measured with the ALICE detector as a function of the invariant mass mee and the pair transverse momentum pT, ee in the ranges mee < 3.5 GeV/c2 and pT, ee < 8 GeV/c, in both collision systems. In proton–proton collisions, the charm and beauty cross sections are determined at midrapidity from a fit to the data with two different event generators. This complements the existing dielectron measurements performed at √s = 7 and 13 TeV. The slope of the √s dependence of the three measurements is…
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.
Measurement of pion, kaon and proton production in proton–proton collisions at \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\sqrt{s} = 7$$\end{document}s=7 TeV
The measurement of primary \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\pi ^{\pm }$$\end{document}π±, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$K^{\pm }$$\end{document}K±, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrs…
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 ...
Measurement of the cross-section for W boson production in association with b-jets in pp collisions at root s=7 TeV with the ATLAS detector
This paper reports a measurement of the W +b-jets (W +b+ X and W + b[¯ over b] +X) production cross-section in proton-proton collisions at a centre-of-mass energy of 7 TeV at the LHC. These results are based on data corresponding to an integrated luminosity of 4.6 fb[superscript −1], collected with the ATLAS detector. Cross-sections are presented as a function of jet multiplicity and of the transverse momentum of the leading b-jet for both the muon and electron decay modes of the W boson. The W +b-jets cross-section, corrected for all known detector effects, is quoted in a limited kinematic range. Combining the muon and electron channels, the fiducial cross-section for W +b-jets is measured…
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 ...
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 ...
Production of K\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$^{*}$$\end{document}∗(892)\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$^{0}$$\end{document}0 and \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\phi $$\end{document}ϕ(1020) in p–Pb collisions at \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\sqrt{s_{{\text {NN}}}}$$\end{document}sNN = 5.02 TeV
The production of K\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$^{*}$$\end{document}∗(892)\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$^{0}$$\end{document}0 and \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage…
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…
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.
Measurement of the branching fraction of the decay Bs0→KS0KS0
A measurement of the branching fraction of the decay Bs0→KS0KS0 is performed using proton-proton collision data corresponding to an integrated luminosity of 5 fb-1 collected by the LHCb experiment between 2011 and 2016. The branching fraction is determined to be B(Bs0→KS0KS0)=[8.3±1.6(stat)±0.9(syst)±0.8(norm)±0.3(fs/fd)]×10-6, where the first uncertainty is statistical, the second is systematic, and the third and fourth are due to uncertainties on the branching fraction of the normalization mode B0→φKS0 and the ratio of hadronization fractions fs/fd. This is the most precise measurement of this branching fraction to date. Furthermore, a measurement of the branching fraction of the decay B0…
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 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.…
Direct photon production in Pb–Pb collisions atsNN=2.76 TeV
Direct photon production at mid-rapidity in Pb–Pb collisions at √sNN = 2.76 TeV was studied in the transverse momentum range 0.9<pT<14 GeV/c. Photons were detected with the highly segmented electromagnetic calorimeter PHOS and via conversions in the ALICE detector material with the e+e− pair reconstructed in the central tracking system. The results of the two methods were combined and direct photon spectra were measured for the 0–20%, 20–40%, and 40–80% centrality classes. For all three classes, agreement was found with perturbative QCD calculations for pT≳5 GeV/c. Direct photon spectra down to pT≈1 GeV/c could be extracted for the 20–40% and 0–20% centrality classes. The significance of th…
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…
Kaon femtoscopy in Pb-Pb collisions at √sNN=2.76 TeV
We present the results of three-dimensional femtoscopic analyses for charged and neutral kaons recorded by ALICE in Pb-Pb collisions at √ s NN = 2.76 TeV. Femtoscopy is used to measure the space-time characteristics of particle production from the effects of quantum statistics and final-state interactions in two-particle correlations. Kaon femtoscopy is an important supplement to that of pions because it allows one to distinguish between different model scenarios working equally well for pions. In particular, we compare the measured three-dimensional kaon radii with a purely hydrodynamical calculation and a model where the hydrodynamic phase is followed by a hadronic rescattering stage. The…
Precision measurement of the mass difference between light nuclei and anti-nuclei
The measurement of the mass differences for systems bound by the strong force has reached a very high precision with protons and anti-protons. The extension of such measurement from (anti-)baryons to (anti-)nuclei allows one to probe any difference in the interactions between nucleons and anti-nucleons encoded in the (anti-)nuclei masses. This force is a remnant of the underlying strong interaction among quarks and gluons and can be described by effective theories, but cannot yet be directly derived from quantum chromodynamics. Here we report a measurement of the difference between the ratios of the mass and charge of deuterons and anti-deuterons, and $^{3}{\rm He}$ and $^3\overline{\rm He}…
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 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…
Study of cosmic ray events with high muon multiplicity using the ALICE detector at the CERN Large Hadron Collider
ALICE is one of four large experiments at the CERN Large Hadron Collider near Geneva, specially designed to study particle production in ultra-relativistic heavy-ion collisions. Located 52 meters underground with 28 meters of overburden rock, it has also been used to detect muons produced by cosmic ray interactions in the upper atmosphere. In this paper, we present the multiplicity distribution of these atmospheric muons and its comparison with Monte Carlo simulations. This analysis exploits the large size and excellent tracking capability of the ALICE Time Projection Chamber. A special emphasis is given to the study of high multiplicity events containing more than 100 reconstructed muons a…
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 ...
Centrality and pseudorapidity dependence of the charged-particle multiplicity density in Xe–Xe collisions at sNN=5.44TeV
In this Letter, the ALICE Collaboration presents the first measurements of the charged-particle multiplicity density, dNch/dη, and total charged-particle multiplicity, Nchtot, in Xe–Xe collisions at a centre-of-mass energy per nucleon–nucleon pair of sNN=5.44TeV. The measurements are performed as a function of collision centrality over a wide pseudorapidity range of −3.5<η<5. The values of dNch/dη at mid-rapidity and Nchtot for central collisions, normalised to the number of nucleons participating in the collision (Npart) as a function of sNN follow the trends established in previous heavy-ion measurements. The same quantities are also found to increase as a function of Npart, and up …
Beauty production in pp collisions at s=2.76 TeV measured via semi-electronic decays
The ALICE Collaboration at the LHC reports measurement of the inclusive production cross section of electrons from semi-leptonic decays of beauty hadrons with rapidity |y|<0.8 and transverse momentum 1<pT<10 GeV/c, in pp collisions at s=2.76 TeV. Electrons not originating from semi-electronic decay of beauty hadrons are suppressed using the impact parameter of the corresponding tracks. The production cross section of beauty decay electrons is compared to the result obtained with an alternative method which uses the distribution of the azimuthal angle between heavy-flavour decay electrons and charged hadrons. Perturbative QCD predictions agree with the measured cross section within the exper…
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…
Measurement of dielectron production in central Pb-Pb collisions at √sNN = 2.76 TeV
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. The first measurement of dielectron (e + e −) production in central (0 – 10 %) Pb – Pb collisions at √sNN=2.76TeV at the LHC is presented. The dielectron invariant-mass spectrum is compared to the expected contributions from hadron decays in the invariant-mass range 0 < mee < 3.5 GeV / c2. The ratio of data and the cocktail of hadronic contributions without vacuum ρ0 is measured in the invariant-mass range 0.15 < mee < 0.7 GeV / c2, w…
Elliptic Flow in Pb-Pb Collisions at
We report a precise measurement of the J/ψ elliptic flow in Pb-Pb collisions at sNN=5.02 TeV with the ALICE detector at the LHC. The J/ψ mesons are reconstructed at midrapidity (|y|<0.9) in the dielectron decay channel and at forward rapidity (2.5<y<4.0) in the dimuon channel, both down to zero transverse momentum. At forward rapidity, the elliptic flow v2 of the J/ψ is studied as a function of the transverse momentum and centrality. A positive v2 is observed in the transverse momentum range 2<pT<8 GeV/c in the three centrality classes studied and confirms with higher statistics our earlier results at sNN=2.76 TeV in semicentral collisions. At midrapidity, the J/ψ v2 is investigated as …
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…
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.
Overview of the JET results in support to ITER
The 2014–2016 JET results are reviewed in the light of their significance for optimising the ITER research plan for the active and non-active operation. More than 60 h of plasma operation with ITER first wall materials successfully took place since its installation in 2011. New multi-machine scaling of the type I-ELM divertor energy flux density to ITER is supported by first principle modelling. ITER relevant disruption experiments and first principle modelling are reported with a set of three disruption mitigation valves mimicking the ITER setup. Insights of the L–H power threshold in Deuterium and Hydrogen are given, stressing the importance of the magnetic configurations and the recent m…
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…
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 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 ...
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…
Measurement of quarkonium production at forward rapidity in \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\mathbf {pp}$$\end{document}pp collisions at \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\mathbf {\sqrt{s}=7}~$$\end{document}s=7TeV
The inclusive production cross sections at forward rapidity of \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\mathrm{J}/\psi }$$\end{document}J/ψ, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\psi (\mathrm{2S})}$$\end{document}ψ(2S), \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} …
Centrality dependence of charged jet production in p–Pb collisions at \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\sqrt{s_\mathrm{NN}}$$\end{document}sNN = 5.02 TeV
Measurements of charged jet production as a function of centrality are presented for p–Pb collisions recorded at \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\sqrt{s_\mathrm {NN}}= 5.02$$\end{document}sNN=5.02 TeV with the ALICE detector. Centrality classes are determined via the energy deposit in neutron calorimeters at zero degree, close to the beam direction, to minimise dynamical biases of the selection. The corresponding number of participants or binary nucleon–nucleon collisions is determined based on…
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 < 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 < 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…
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…
Measurement of Z 0 -boson production at large rapidities in Pb–Pb collisions at
The production of Z0 bosons at large rapidities in Pb–Pb collisions at √sNN=5.02TeV is reported. Z0 candidates are reconstructed in the dimuon decay channel (Z0→μ+μ−), based on muons selected with pseudo-rapidity −4.0 20GeV/c. The invariant yield and the nuclear modification factor, RAA, are presented as a function of rapidity and collision centrality. The value of RAA for the 0–20% central Pb–Pb collisions is 0.67±0.11(stat.)±0.03(syst.)±0.06(corr. syst.), exhibiting a deviation of 2.6σ from unity. The results are well-described by calculations that include nuclear modifications of the parton distribution functions, while the predictions using vacuum PDFs deviate from data by 2.3σ in the 0…
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 quark contact interactions in dijet angular distributions in pp collisions at s=7 TeV measured with the ATLAS detector
Dijet angular distributions from the first LHC pp collisions at center-of-mass energy sqrt(s) = 7 TeV have been measured with the ATLAS detector. The dataset used for this analysis represents an integrated luminosity of 3.1 pb-1. Dijet $\chi$ distributions and centrality ratios have been measured up to dijet masses of 2.8 TeV, and found to be in good agreement with Standard Model predictions. Analysis of the $\chi$ distributions excludes quark contact interactions with a compositeness scale $\Lambda$ below 3.4 TeV, at 95% confidence level, significantly exceeding previous limits.
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 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…
Measurement of electrons from heavy-flavour hadron decays in p–Pb collisions at sNN=5.02TeV
The production of electrons from heavy-flavour hadron decays was measured as a function of transverse momentum (pT) in minimum-bias p–Pb collisions at √sNN = 5.02 TeV using the ALICE detector at the LHC. The measurement covers the pT interval 0.5 < pT < 12 GeV/c and the rapidity range −1.065 < ycms < 0.135 in the centre-of-mass reference frame. The contribution of electrons from background sources was subtracted using an invariant mass approach. The nuclear modification factor RpPb was calculated by comparing the pT-differential invariant cross section in p–Pb collisions to a pp reference at the same centre-of-mass energy, which was obtained by interpolating measurements at √s = 2.76 TeV an…
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 …
Centrality determination of Pb-Pb collisions atsNN=2.76TeV with ALICE
This publication describes the methods used to measure the centrality of inelastic Pb-Pb collisions at a center-of-mass energy of 2.76 TeV per colliding nucleon pair with ALICE. The centrality is a key parameter in the study of the properties of QCD matter at extreme temperature and energy density, because it is directly related to the initial overlap region of the colliding nuclei. Geometrical properties of the collision, such as the number of participating nucleons and the number of binary nucleon-nucleon collisions, are deduced from a Glauber model with a sharp impact parameter selection and shown to be consistent with those extracted from the data. The centrality determination provides …
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.
Measurements of mixed harmonic cumulants in Pb–Pb collisions at sNN=5.02 TeV
Correlations between moments of different flow coefficients are measured in Pb–Pb collisions at sNN=5.02 TeV recorded with the ALICE detector. These new measurements are based on multiparticle mixed harmonic cumulants calculated using charged particles in the pseudorapidity region |η|<0.8 with the transverse momentum range 0.2<pT<5.0 GeV/c. The centrality dependence of correlations between two flow coefficients as well as the correlations between three flow coefficients, both in terms of their second moments, are shown. In addition, a collection of mixed harmonic cumulants involving higher moments of v2 and v3 is measured for the first time, where the characteristic signature of ne…
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 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 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 …
Centrality dependence ofπ,K, andpproduction in Pb-Pb collisions atsNN=2.76TeV
In this paper measurements are presented of pi(+/-), K-+/-, p, and (p) over bar production at midrapidity (vertical bar y vertical bar < 0.5), in Pb-Pb collisions at root s(NN) = 2.76 TeV as a function of centrality. The measurement covers the transverse-momentum (p(T)) range from 100, 200, and 300 MeV/c up to 3, 3, and 4.6 GeV/c for pi, K, and p, respectively. The measured p(T) distributions and yields are compared to expectations based on hydrodynamic, thermal and recombination models. The spectral shapes of central collisions show a stronger radial flow than measured at lower energies, which can be described in hydrodynamic models. In peripheral collisions, the p(T) distributions are not…
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…
Energy dependence of the transverse momentum distributions of charged particles in pp collisions measured by ALICE
Differential cross sections of charged particles in inelastic pp collisions as a function of $p_{\rm T}$ have been measured at $\sqrt{s}=$ 0.9, 2.76 and 7 TeV at the LHC. The $p_{\rm T}$ spectra are compared to NLO-pQCD calculations. Though the differential cross section for an individual $\sqrt{s}$ cannot be described by NLO-pQCD, the relative increase of cross section with $\sqrt{s}$ is in agreement with NLO-pQCD. Based on these measurements and observations, procedures are discussed to construct pp reference spectra at $\sqrt{s} =$ 2.76 and 5.02 TeV up to $p_{\rm T}$ = 50 GeV/$c$ as required for the calculation of the nuclear modification factor in nucleus-nucleus and proton-nucleus coll…
Measurement of visible cross sections in proton-lead collisions at √sNN= 5.02 TeV in van der Meer scans with the ALICE detector
In 2013, the Large Hadron Collider provided proton-lead and lead-proton collisions at the center-of-mass energy per nucleon pair $\sqrt{s_{\rm{NN}}}=5.02$ TeV. Van der Meer scans were performed for both configurations of colliding beams, and the cross section was measured for two reference processes, based on particle detection by the T0 and V0 detectors, with pseudo-rapidity coverage $4.6<\eta< 4.9$, $-3.3<\eta<-3.0$ and $2.8<\eta< 5.1$, $-3.7<\eta<-1.7$, respectively. Given the asymmetric detector acceptance, the cross section was measured separately for the two configurations. The measured visible cross sections are used to calculate the integrated luminosity of the proton-lead and lead-…
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…
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…
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 ...
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…
Modelling of JET hybrid plasmas with emphasis on performance of combined ICRF and NBI heating
International audience; During the 2015--2016 JET campaigns, many efforts have been devoted to the exploration of high-performance plasma scenarios envisaged for DT operation in JET. In this paper, we review various key recent hybrid discharges and model the combined ICRF NBI heating. These deuterium discharges with deuterium beams had the ICRF antenna frequency tuned to match the cyclotron frequency of minority H at the centre of the tokamak coinciding with the second harmonic cyclotron resonance of D. The modelling takes into account the synergy between ICRF and NBI heating through the second harmonic cyclotron resonance of D beam ions, allowing us to assess its impact on the neutron rate…
Search for stable hadronising squarks and gluinos with the ATLAS experiment at the LHC
Hitherto unobserved long-lived massive particles with electric and/or colour charge are predicted by a range of theories which extend the Standard Model. In this Letter a search is performed at the ATLAS experiment for slow-moving charged particles produced in proton–proton collisions at 7 TeV centre-of-mass energy at the LHC, using a data-set corresponding to an integrated luminosity of 34 pb[superscript −1]. No deviations from Standard Model expectations are found. This result is interpreted in a framework of supersymmetry models in which coloured sparticles can hadronise into long-lived bound hadronic states, termed R-hadrons, and 95% CL limits are set on the production cross-sections of…
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…
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 ...
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…