0000000000252713
AUTHOR
Christian Zeitnitz
Determination of the LEP centre-of-mass energy from Zγ events
Radiative returns to the Z resonance (Zgamma events) are used to determine the LEP2 centre-of-mass energy from the data collected with the ALEPH detector in 1997. The average centre-of-mass energy is measured to be: E_CM = 182.50 +- 0.19(stat) +- 0.08(syst) GeV in good agreement with the precise determination by the LEP energy working group of 182.652 +- 0.050 GeV. If applied to the measurement of the W mass, its precision translates into a systematic error on M_W which is smaller than the statistical error achieved from the corresponding dataset.
Observation of the Doubly StrangebBaryonΩb−
We report the observation of the doubly strange b baryon Omega(-)(b) in the decay channel Omega(-)(b) -> J/psi Omega(-), with J/psi -> mu(+)mu(-) and Omega(-) -> Lambda K- -> (p pi(-))K-, in p (p) over bar collisions at root s = 1.96 TeV. Using approximately 1.3 fb(-1) of data collected with the D0 detector at the Fermilab Tevatron Collider, we observe 17.8 +/- 4.9(stat) +/- 0.8(syst) Omega(-)(b) signal events at a mass of 6.165 +/- 0.010(stat) +/- 0.013(syst) GeV. The significance of the observed signal is 5.4 sigma, corresponding to a probability of 6.7 x 10(-8) of it arising from a background fluctuation.
Search for pairs of highly collimated photon-jets in pp collisions at s=13 TeV with the ATLAS detector
Results of a search for the pair production of photon-jets - collimated groupings of photons - in the ATLAS detector at the Large Hadron Collider are reported. Highly collimated photon-jets can arise from the decay of new, highly boosted particles that can decay to multiple photons collimated enough to be identified in the electromagnetic calorimeter as a single, photonlike energy cluster. Data from proton-proton collisions at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 36.7 fb-1, were collected in 2015 and 2016. Candidate photon-jet pair production events are selected from those containing two reconstructed photons using a set of identification criteria …
Search forZZandZγ*Production inpp¯Collisions ats=1.96 TeVand Limits on AnomalousZZZandZZγ*Couplings
We present a study of mu mu mu mu, eeee, and mu mu ee events using 1 fb(-1) of data collected with the D0 detector at the Fermilab Tevatron p (p) over bar Collider at root s = 1.96 TeV. Requiring t ...
Search for γγ→ηb in e+e− collisions at LEP 2
A search for the pseudoscalar meson eta_b is performed in two-photon interactions at LEP~2 with an integrated luminosity of 699 pb^-1 collected at e+e- centre-of-mass energies from 181 GeV to 209 GeV. One candidate event is found in the six-charged-particle final state and none in the four-charged-particle final state, in agreement with the total expected background of about one event. Upper limits of Gamma_gammagamma(eta_b) * BR(eta_b -> 4 charged particles) 6 charged particles) < 132 eV are obtained at 95% confidence level, which correspond to 95% confidence level upper limits of 9.0% and 25% on these branching ratios.
Search for the Higgs Boson inH→WW(*)Decays inpp¯Collisions ats=1.96 TeV
We present a search for the standard model Higgs boson in H --> WW(*) decays with e+e-, e+/-mu-/+, and mu+mu- final states in pp collisions at a center-of-mass energy of square root of s = 1.96 TeV. The data, collected from April 2002 to June 2004 with the D0 detector, correspond to an integrated luminosity of 300-325 pb(-1), depending on the final state. The number of events observed is consistent with the expectation from backgrounds. Limits from the combination of all three channels on the Higgs boson production cross section times branching ratio sigma x BR(H --> WW(*) are presented.
Four-jet final state production in e+e- collisions at centre-of-mass energies of 130 and 136 GeV
The four-jet final state is analyzed to search for hadronic decays of pair-produced heavy particles. The analysis uses the ALEPH data collected at LEP in November 1995 at centre-of-mass energies of 130 and 136 GeV, corresponding to a total integrated luminosity of 5.7 pb(-1). An excess of four-jet events is observed with respect to the standard model predictions. In addition, these events exhibit an enhancement in the sum of the two di-jet masses around 105 GeV/c(2). The properties of these events are studied and compared to the expectations from standard processes and to pair production hypotheses. RI ANTONELLI, ANTONELLA/C-6238-2011; Passalacqua, Luca/F-5127-2011; Murtas, Fabrizio/B-5729-…
A purity monitoring system for liquid argon calorimeters
Abstract For liquid argon calorimeters electronegative impurities dissolved in the medium degrade the detector response and deteriorate the energy resolution, especially at high energies. A concept for a purity monitoring system for liquid argon calorimeters has been developed and is presented here. Special combined monitors of 241 Am- and 207 Bi-cells are used to monitor the concentration of impurities. The working principle as well as results from test measurements are discussed.
Search for admixture of scalar top quarks in the tt¯ lepton + jets final state at s=1.96 TeV
A search for pair production of the lightest supersymmetric partner of the top quark is performed in the lepton+jets channel using 0.9 fb-1 of data collected by the D0 experiment. Kinematic differences between scalar top quark pair production and the dominant top quark pair production background are used to separate the two processes. First limits from Run II of the Fermilab Tevatron Collider for the scalar top quark decaying to a chargino and a b quark are obtained for scalar top quark masses of 130-190 GeV and chargino masses of 90-150 GeV.
Search for Third-Generation Scalar Leptoquarks inpp¯Collisions ats=1.96 TeV
We report on a search for charge-1/3 third-generation leptoquarks (LQ) produced in p (p) over bar collisions at root s =1.96 TeV using the D0 detector at Fermilab. Third-generation leptoquarks are assumed to be produced in pairs and to decay to a tau neutrino and a b quark with branching fraction B. We place upper limits on sigma(p (p) over bar -> LQ (LQ) over bar )B-2 as a function of the leptoquark mass M-LQ. Assuming B=1, we exclude at the 95% confidence level third-generation scalar leptoquarks with M-LQ < 229 GeV.
Dijet azimuthal correlations and conditional yields in pp and p+Pb collisions at sNN=5.02TeV with the ATLAS detector
This paper presents a measurement of forward-forward and forward-central dijet azimuthal angular correlations and conditional yields in proton-proton (pp) and proton-lead (p + Pb) collisions as a p ...
Measurements of four-lepton production in pp collisions at s=8 TeV with the ATLAS detector
A search is presented for a high-mass Higgs boson in the , , , and decay modes using the ATLAS detector at the CERN Large Hadron Collider. The search uses proton-proton collision data at a centre-o ...
Search for anomalous electroweak production of WW/WZ in association with a high-mass dijet system in pp collisions at s=8 TeV with the ATLAS detector
A search is presented for anomalous quartic gauge boson couplings in vector-boson scattering. The data for the analysis correspond to $20.2$ fb$^{-1}$ of $\sqrt{s}=8$ TeV $pp$ collisions, and were collected in 2012 by the ATLAS experiment at the Large Hadron Collider. The search looks for the production of $WW$ or $WZ$ boson pairs accompanied by a high-mass dijet system, with one $W$ decaying leptonically, and a $W$ or $Z$ decaying hadronically. The hadronically decaying $W/Z$ is reconstructed as either two small-radius jets or one large-radius jet using jet substructure techniques. Constraints on the anomalous quartic gauge boson coupling parameters $\alpha_4$ and $\alpha_5$ are set by fit…
Relative luminosity measurement of the LHC with the ATLAS forward calorimeter
In this paper it is shown that a measurement of the relative luminosity changes at the LHC may be obtained by analysing the currents drawn from the high voltage power supplies of the electromagnetic section of the forward calorimeter of the ATLAS detector. The method was verified with a reproduction of a small section of the ATLAS forward calorimeter using proton beams of known beam energies and variable intensities at the U-70 accelerator at IHEP in Protvino, Russia. The experimental setup and the data taking during a test beam run in April 2008 are described in detail. A comparison of the measured high voltage currents with reference measurements from beam intensity monitors shows a linea…
Measurement of inclusive jet charged-particle fragmentation functions in Pb+Pb collisions at sNN=2.76 TeV with the ATLAS detector
Measurements of charged-particle fragmentation functions of jets produced in ultra-relativistic nuclear collisions can provide insight into the modification of parton showers in the hot, dense medi ...
Performance of the ATLAS liquid argon endcap calorimeter in the pseudorapidity region in beam tests
Abstract The pseudorapidity region 2.5 | η | 4.0 in ATLAS is a particularly complex transition zone between the endcap and forward calorimeters. A set-up consisting of 1 4 resp. 1 8 of the full azimuthal acceptance of the ATLAS liquid argon endcap and forward calorimeters has been exposed to beams of electrons, pions and muons in the energy range E ⩽ 200 GeV at the CERN SPS. Data have been taken in the endcap and forward calorimeter regions as well as in the transition region. This beam test set-up corresponds very closely to the geometry and support structures in ATLAS. A detailed study of the performance in the endcap and forward calorimeter regions is described. The data are compared wit…
Measurement of theΛb0Lifetime in the DecayΛb0→J/ψΛ0with the D0 Detector
We present measurements of the Lambda(b)(0) lifetime in the exclusive decay channel Lambda(b)(0)-> J/psi Lambda(0), with J/psi ->mu(+)mu(-) and Lambda(0)-> p pi(-), the B-0 lifetime in the decay B-0-> J/psi K-S(0) with J/psi ->mu(+)mu(-) and K-S(0)->pi(+)pi(-), and the ratio of these lifetimes. The analysis is based on approximately 250 pb(-1) of data recorded with the D0 detector in p (p) over bar collisions at root s = 1.96 TeV. The Lambda(b)(0) lifetime is determined to be tau(Lambda(b)(0))=1.22(-0.18)(+0.22)(stat)+/- 0.04(syst) ps, the B-0 lifetime tau(B-0)=1.40(-) (+0.11)(0.10)(stat)+/- 0.03(syst) ps, and the ratio tau(Lambda(b)(0))/tau(B-0)=0.87(-) (+0.17)(0.14)(stat)+/- 0.03(syst). I…
Search for high-mass dilepton resonances using 139 fb−1 of pp collision data collected at s=13 TeV with the ATLAS detector
A search for high-mass dielectron and dimuon resonances in the mass range of 250 GeV to 6 TeV is presented. The data were recorded by the ATLAS experiment in proton–proton collisions at a centre-of-mass energy of s=13 TeV during Run 2 of the Large Hadron Collider and correspond to an integrated luminosity of 139 fb −1 . A functional form is fitted to the dilepton invariant-mass distribution to model the contribution from background processes, and a generic signal shape is used to determine the significance of observed deviations from this background estimate. No significant deviation is observed and upper limits are placed at the 95% confidence level on the fiducial cross-section times bran…
Search for Higgs bosons decaying toaain theμμττfinal state inppcollisions ats=8 TeVwith the ATLAS experiment
A search for the decay to a pair of new particles of either the 125 GeV Higgs boson (h) or a second charge parity (CP)-even Higgs boson (H) is presented. The data set corresponds to an integrated luminosity of 20.3 fb(-1) of pp collisions at root s = 8 TeV recorded by the ATLAS experiment at the LHC in 2012. The search was done in the context of the next-to-minimal supersymmetric standard model, in which the new particles are the lightest neutral pseudoscalar Higgs bosons (a). One of the two a bosons is required to decay to two muons while the other is required to decay to two tau leptons. No significant excess is observed above the expected backgrounds in the dimuon invariant mass range fr…
Transverse momentum correlations in hadronic Z decays
Using data obtained with the ALEPH detector at the Z resonance, a measure based on transverse momentum is shown to exhibit a correlation between the two halves of a hadronic event which cannot be explained by energy-momentum conservation, flavour conservation, the imposition of an event axis or imperfect event reconstruction. Two possible interpretations based on existing Monte Carlo models are examined: a) ARIADNE, with the correlation forming early in the parton shower and with the transition from partons to hadrons playing only a minor part; b) JETSET, with the correlation forming at the fragmentation stage. A correlation technique based on a jet cluster analysis is used to make a compar…
Search for long-lived particles produced in pp collisions at s=13 TeV that decay into displaced hadronic jets in the ATLAS muon spectrometer
A search for the decay of neutral, weakly interacting, long-lived particles using data collected by the ATLAS detector at the LHC is presented. The analysis in this paper uses 36.1 fb(-1) of proton ...
Search for the rare decayBs0→ϕμ+μ−with the D0 detector
We present a search for the flavor-changing neutral current decay B-s(0)->phi mu(+)mu(-) using about 0.45 fb(-1) of data collected in p (p) over bar collisions at root s=1.96 TeV with the D0 detector at the Fermilab Tevatron Collider. We find an upper limit on the branching ratio of this decay normalized to B-s(0)-> J/psi phi of B(B-s(0)->phi mu(+)mu(-))/B(B-s(0)-> J/psi phi) J/psi phi, the limit corresponds to B(B-s(0)->phi mu(+)mu(-))< 4.1x10(-6) at the 95% C.L., the most stringent upper bound to date.
Search for an excess of events with an identical flavour lepton pair and significant missing transverse momentum in root s=7 TeV proton-proton collisions with the ATLAS detector
Results are presented of a search for supersymmetric particles decaying into final states with significant missing transverse momentum and exactly two identical flavour leptons (e or mu) of opposite charge in sqrt{s}=7 TeV collisions at the Large Hadron Collider. This channel is particularly sensitive to supersymmetric particle cascade decays producing flavour correlated lepton pairs. Flavour uncorrelated backgrounds are subtracted using a sample of opposite flavour lepton pair events. Observation of an excess beyond Standard Model expectations following this subtraction procedure would offer one of the best routes to measuring the masses of supersymmetric particles. In a data sample corres…
Search for Pair Production of Scalar Bottom Quarks inpp¯Collisions ats=1.96 TeV
A search for direct production of scalar bottom quarks ((b) over bar) is performed with 310 pb(-1) of data collected by the D0 experiment in p (p) over bar collisions at root s = 1.96 TeV at the Fermilab Tevatron Collider. The topology analyzed consists of two b jets and an imbalance in transverse momentum due to undetected neutralinos (chi(0)(1)), with chi(0)(1) assumed to be the lightest supersymmetric particle. We find the data consistent with standard model expectations, and set a 95% C.L. exclusion domain in the (m(b), m(chi 1)(0)) mass plane, improving significantly upon the results from run I of the Tevatron.
Search for right-handed W bosons in top quark decay
We present a measurement of the fraction f+ of right-handed W bosons produced in top quark decays, based on a candidate sample of $t\bar{t}$ events in the lepton+jets decay mode. These data correspond to an integrated luminosity of 230pb^-1, collected by the DO detector at the Fermilab Tevatron $p\bar{p}$ Collider at sqrt(s)=1.96 TeV. We use a constrained fit to reconstruct the kinematics of the $t\bar{t}$ and decay products, which allows for the measurement of the leptonic decay angle $\theta^*$ for each event. By comparing the $\cos\theta^*$ distribution from the data with those for the expected background and signal for various values of f+, we find f+=0.00+-0.13(stat)+-0.07(syst). This …
Study of the DecayBs0→Ds(*)Ds(*)
We report a study of the decay B-s(0)->(DsDs(*))-D-(*) using a data sample corresponding to 1.3 fb(-1) of integrated luminosity collected by the D0 experiment in 2002-2006 during run II of the F ...
Search for light resonances decaying to boosted quark pairs and produced in association with a photon or a jet in proton–proton collisions at s=13TeV with the ATLAS detector
This Letter presents a search for new light resonances decaying to pairs of quarks and produced in association with a high- pT photon or jet. The dataset consists of proton–proton collisions with an integrated luminosity of 36.1 fb −1 at a centre-of-mass energy of s=13 TeV recorded by the ATLAS detector at the Large Hadron Collider. Resonance candidates are identified as massive large-radius jets with substructure consistent with a particle decaying into a quark pair. The mass spectrum of the candidates is examined for local excesses above background. No evidence of a new resonance is observed in the data, which are used to exclude the production of a lepto-phobic axial-vector Z′ boson.
Properties of jet fragmentation using charged particles measured with the ATLAS detector in pp collisions at s=13 TeV
This paper presents a measurement of quantities related to the formation of jets from high-energy quarks and gluons (fragmentation). Jets with transverse momentum 100 GeV 500 MeV and vertical bar ...
Measurement ofσ(pp¯→Z)·Br(Z→ττ)ats=1.96 TeV
We present a measurement of the cross section for Z production times the branching fraction to tau leptons, sigma.Br(Z ->tau(+)tau(-)), in p (p) over bar collisions at root s=1.96 TeV in the channel in which one tau decays into mu nu(mu)nu(tau), and the other into hadrons+nu(tau) or e nu(e)nu(tau). The data sample corresponds to an integrated luminosity of 226 pb(-1) collected with the D0 detector at the Fermilab Tevatron collider. The final sample contains 2008 candidate events with an estimated background of 55%. From this we obtain sigma.Br(Z ->tau(+)tau(-)) = 237 +/- 15(stat)+/- 18(sys)+/- 15(lum)pb, in agreement with the standard model prediction.
Measurement of jet fragmentation in Pb+Pb and pp collisions at sNN=5.02 TeV with the ATLAS detector
This paper presents a measurement of jet fragmentation functions in 0.49 nb−1 of Pb+Pb collisions and 25 pb−1 of pp collisions at √sNN=5.02 TeV collected in 2015 with the ATLAS detector at the LHC. These measurements provide insight into the jet quenching process in the quark-gluon plasma created in the aftermath of ultrarelativistic collisions between two nuclei. The modifications to the jet fragmentation functions are quantified by dividing the measurements in Pb+Pb collisions by baseline measurements in pp collisions. This ratio is studied as a function of the transverse momentum of the jet, the jet rapidity, and the centrality of the collision. In both collision systems, the jet fragmen…
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…
Search for a Structure in the Bs0π± Invariant Mass Spectrum with the ATLAS Experiment
A search for the narrow structure, X(5568), reported by the D0 Collaboration in the decay sequence X→B_{s}^{0}π^{±}, B_{s}^{0}→J/ψϕ, is presented. The analysis is based on a data sample recorded with the ATLAS detector at the LHC corresponding to 4.9 fb^{-1} of pp collisions at 7 TeV and 19.5 fb^{-1} at 8 TeV. No significant signal was found. Upper limits on the number of signal events, with properties corresponding to those reported by D0, and on the X production rate relative to B_{s}^{0} mesons, ρ_{X}, were determined at 95% confidence level. The results are N(X)<382 and ρ_{X}<0.015 for B_{s}^{0} mesons with transverse momenta above 10 GeV, and N(X)<356 and ρ_{X}<0.016 for transverse m…
Study of the hard double-parton scattering contribution to inclusive four-lepton production in pp collisions at s=8 TeV with the ATLAS detector
The inclusive production of four isolated charged leptons in pp collisions is analysed for the presence of hard double-parton scattering, using 20.2 fb(-1) of data recorded in the ATLAS detector at ...
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 ...
Measurements of the Total and Differential Higgs Boson Production Cross Sections Combining theH→γγandH→ZZ*→4ℓDecay Channels ats=8 TeVwith the ATLAS Detector
Measurements of the total and differential cross sections of Higgs boson production are performed using 20.3 fb(-1) of pp collisions produced by the Large Hadron Collider at a center-of-mass energy of root s = 8 TeV and recorded by the ATLAS detector. Cross sections are obtained from measured H -> gamma gamma and H -> ZZ*. 4l event yields, which are combined accounting for detector efficiencies, fiducial acceptances, and branching fractions. Differential cross sections are reported as a function of Higgs boson transverse momentum, Higgs boson rapidity, number of jets in the event, and transverse momentum of the leading jet. The total production cross section is determined to be sigma(pp -> …
Measurement of theBs0Lifetime in the Exclusive Decay ChannelBs0→J/ψϕ
Using the exclusive decay B-s(0)-->J/psi(mu(+)mu(-))phi(K+K-), we report the most precise single measurement of the B-s(0) lifetime. The data sample corresponds to an integrated luminosity of approximately 220 pb(-1) collected with the D0 detector at the Fermilab Tevatron Collider in 2002-2004. We reconstruct 337 signal candidates, from which we extract the B-s(0) lifetime, tau(B-s(0))=1.444(-0.090)(+0.098)(stat)+/-0.020(sys) ps. We also report a measurement for the lifetime of the B-0 meson using the exclusive decay B-0-->J/psi(mu(+)mu(-))K-*0(892)(K(+)pi(-)). We reconstruct 1370 signal candidates, obtaining tau(B-0)=1.473(-0.050)(+0.052)(stat)+/-0.023(sys) ps, and the ratio of lifetimes, …
Search for Low-Mass Dijet Resonances Using Trigger-Level Jets with the ATLAS Detector in pp Collisions at s=13 TeV
Searches for dijet resonances with sub-TeV masses using the ATLAS detector at the Large Hadron Collider can be statistically limited by the bandwidth available to inclusive single-jet triggers, who ...
Search for $\gamma\gamma$ decays of a Higgs boson produced in association with a fermion pair in $e^+ e^-$ collisions at LEP
A serach for gamma gamma decays of Higgs boson is performed in the data sample collected at LEP with the ALEPH detector between 1991 and 1999. This corresponds to an integrated luminosity of 672 pb-1 centre-of-mass energies ranging from 88 to 202 GeV. The search is based on topologies arising from a Higgs boson produced in association with a fermion pair via the Higgs-strahlung process e+e- -> Hffbar, with ffbar = nunubar, e+e-, mu+mu-, tau+tau- or qqbar... (CERN)
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 Dijet Azimuthal Decorrelations at Central Rapidities inpp¯Collisions ats=1.96 TeV
Correlations in the azimuthal angle between the two largest transverse momentum jets have been measured using the D0 detector in p (p) over bar collisions at a center-of-mass energy root s=1.96 TeV. The analysis is based on an inclusive dijet event sample in the central rapidity region corresponding to an integrated luminosity of 150 pb(-1). Azimuthal correlations are stronger at larger transverse momenta. These are well described in perturbative QCD at next-to-leading order in the strong coupling constant, except at large azimuthal differences where contributions with low transverse momentum are significant.
Hadronic calibration of the ATLAS liquid argon end-cap calorimeter in the pseudorapidity region in beam tests
Abstract A full azimuthal φ -wedge of the ATLAS liquid argon end-cap calorimeter has been exposed to beams of electrons, muons and pions in the energy range 6 GeV ⩽ E ⩽ 200 GeV at the CERN SPS. The angular region studied corresponds to the ATLAS impact position around the pseudorapidity interval 1.6 | η | 1.8 . The beam test setup is described. A detailed study of the performance is given as well as the related intercalibration constants obtained. Following the ATLAS hadronic calibration proposal, a first study of the hadron calibration using a weighting ansatz is presented. The results are compared to predictions from Monte Carlo simulations, based on GEANT 3 and GEANT 4 models.
Search for long-lived particles decaying into electron or photon pairs with the D0 detector
In this Letter we report on a search for long-lived particles that decay into final states with two electrons or photons. Such long-lived particles arise in a variety of theoretical models, like hidden valleys and supersymmetry with gauge-mediated breaking. By precisely reconstructing the direction of the electromagnetic shower we are able to probe much longer lifetimes than previously explored. We see no evidence of the existence of such long-lived particles and interpret this search as a quasi model-independent limit on their production cross section, as well as a limit on a long-lived fourth generation quark.
Search for the Flavor-Changing Neutral Current DecayBs0→μ+μ−inpp¯Collisions ats=1.96 TeVwith the D0 Detector
We present the results of a search for the flavor-changing neutral current decay B-s(0)-->mu(+)mu(-) using a data set with integrated luminosity of 240 pb(-1) of p (p) over bar collisions at roo ...
Search for pair production of Higgsinos in final states with at least three b -tagged jets in s=13 TeV pp collisions using the ATLAS detector
A search for pair production of the supersymmetric partners of the Higgs boson (higgsinos H˜) in gauge-mediated scenarios is reported. Each higgsino is assumed to decay to a Higgs boson and a gravitino. Two complementary analyses, targeting high- and low-mass signals, are performed to maximize sensitivity. The two analyses utilize LHC pp collision data at a center-of-mass energy s=13 TeV, the former with an integrated luminosity of 36.1 fb-1 and the latter with 24.3 fb-1, collected with the ATLAS detector in 2015 and 2016. The search is performed in events containing missing transverse momentum and several energetic jets, at least three of which must be identified as b-quark jets. No sig…
Measurement of jet charge in dijet events froms=8 TeVppcollisions with the ATLAS detector
The momentum-weighted sum of the charges of tracks associated to a jet is sensitive to the charge of the initiating quark or gluon. This paper presents a measurement of the distribution of momentum ...
Luminosity determination in pp collisions at s=7 TeV using the ATLAS detector at the LHC
Measurements of luminosity obtained using the ATLAS detector during early running of the Large Hadron Collider (LHC) at s√=7 TeV are presented. The luminosity is independently determined using several detectors and multiple algorithms, each having different acceptances, systematic uncertainties and sensitivity to background. The ratios of the luminosities obtained from these methods are monitored as a function of time and of μ, the average number of inelastic interactions per bunch crossing. Residual time- and μ-dependence between the methods is less than 2% for 0<μ<2.5. Absolute luminosity calibrations, performed using beam separation scans, have a common systematic uncertainty of ±11%, do…
Studies of QCD in ${\rm e^+ e^-}\to $ hadrons at $E_{\rm cm} = 130$ and 136 GeV
Studies of QCD in $\mbox{e}^+\mbox{e}^- \rightarrow$ Hadrons at $E_{cm} = $} 130 and 136 GeV The ALEPH Collaboration An analysis of the properties of hadronic final states produced in electron-positron annihilation at centre-of-mass energies of 130 and 136 GeV is presented. The measurements are based on a data sample of 5.7 $\mbox{pb}^{-1}$ collected in November 1995 with the \Aleph detector at LEP. Inclusive charged particle distributions, jet rates and event-shape distributions are measured and the results are compared with the predictions of QCD-based models. From the measured distributions quantities are determined for which the dependence on the centre-of-mass energy can be predicted b…
Search for large extra spatial dimensions in dimuon production with the D0 detector
We present the results of a search for the effects of large extra spatial dimensions in $p{\bar p}$ collisions at $\sqrt{s} =$ 1.96 TeV in events containing a pair of energetic muons. The data correspond to 246 \ipb of integrated luminosity collected by the \D0 experiment at the Fermilab Tevatron Collider. Good agreement with the expected background was found, yielding no evidence for large extra dimensions. We set 95% C.L. lower limits on the fundamental Planck scale between 0.85 TeV and 1.27 TeV within several formalisms. These are the most stringent limits achieved in the dimuon channel to date.
Resolution of the ATLAS muon spectrometer monitored drift tubes in LHC Run 2
The momentum measurement capability of the ATLAS muon spectrometer relies fundamentally on the intrinsic single-hit spatial resolution of the monitored drift tube precision tracking chambers. Optimal resolution is achieved with a dedicated calibration program that addresses the specific operating conditions of the 354 000 high-pressure drift tubes in the spectrometer. The calibrations consist of a set of timing offsets and drift time to drift distance transfer relations, and result in chamber resolution functions. This paper describes novel algorithms to obtain precision calibrations from data collected by ATLAS in LHC Run 2 and from a gas monitoring chamber, deployed in a dedicated gas fac…
Measurement of σ(pp¯→Z+X)Br(Z→τ+τ−) at s=1.96 TeV
We present a measurement of the cross section for Z boson production times the branching fraction to tau lepton pairs sigma(p (p) over bar -> Z + X)Br(Z -> tau(+)tau(-)) in p (p) over bar collisions at root s = 1.96 TeV. The measurement is performed in the channel in which one tau lepton decays into a muon and neutrinos. and the other tau lepton decays hadronically or into an electron and neutrinos. The data sample corresponds to an integrated luminosity of 1.0 fb(-1) collected with the DO detector at the Fermilab Tevatron Collider. The sample contains 1511 candidate events with an estimated 20% background from jets or muons misidentified as tau leptons. We obtain sigma . Br = 240 +/- 8 (st…
Search for dark matter candidates and large extra dimensions in events with a jet and missing transverse momentum with the ATLAS detector
A search for new phenomena in events with a high-energy jet and large missing transverse momentum is performed using data from proton-proton collisions at √s = 7 TeV with the ATLAS experiment at the Large Hadron Collider. Four kinematic regions are explored using a dataset corresponding to an integrated luminosity of 4.7 fb[superscript −1]. No excess of events beyond expectations from Standard Model processes is observed, and limits are set on large extra dimensions and the pair production of dark matter particles.
Searches for neutral Higgs bosons in e+e− collisions at centre-of-mass energies from 192 to 202 GeV
Searches for neutral Higgs bosons are performed with the 237 pb-1 of data collected in 1999 by the ALEPH detector at LEP, for centre-of-mass energies between 191.6 and 201.6 GeV. These searches apply to Higgs bosons within the context of the Standard Model and its minimal supersymmetric extension (MSSM) as well as to invisibly decaying Higgs bosons. No evidence of a signal is seen. A lower limit on the mass of the Standard Model Higgs boson of 107.7 GeV/c2 at 95% confidence level is set. In the MSSM, lower limits of 91.2 and 91.6 GeV/c2 are derived for the masses of the neutral Higgs bosons h and A, respectively. For a Higgs boson decaying invisibly and produced with the Standard Model cros…
A flavour-independent Higgs boson search in e+e- collisions at sqrt(s) up to 209GeV
A search for the Higgsstrahlung process e+e- → HZ is carried out, covering decays of the Higgs boson into any quark pair, a gluon pair or a tau pair. The analysis is based on the 630 pb-1 of data collected by the ALEPH detector at LEP at centre-of-mass energies from 189 to 209 GeV. A 95% C.L. lower mass limit of 109.1 GeV/c2 is obtained for a Higgs boson cross section equal to that expected from the Standard Model if the Higgs boson decays exclusively into hadrons and/or taus, irrespective of the relative branching fractions. © 2002 Elsevier Science B.V. All rights reserved.
Search for R-parity-violating supersymmetric particles in multi-jet final states produced in p–p collisions at s=13 TeV using the ATLAS detector at the LHC
Results of a search for gluino pair production with subsequent R-parity-violating decays to quarks are presented. This search uses 36.1 fb(-1) of data collected by the ATLAS detector in proton-prot ...
Inclusive production of neutral vector mesons in hadronic Z decays
Data on the inclusive production of the neutral vector mesons rho(0)(770), omega(782), K*(0)(892), and phi (1020) in hadronic Z decays recorded with the ALEPH detector at LEP are presented and compared to Monte Carlo model predictions. Bose-Einstein effects are found to be important in extracting a reliable value for the p(0) production rate. An average p(0) multiplicity of 1.45 +/- 0.21 per event is obtained. The omega is detected via its three pion decay mode omega --> pi(+)pi(-)pi(0) and has a total rate of 1.07 +/- 0.14 per event. The multiplicity of the K*(0) is 0.83 +/- 0.09, whilst that of the phi is 0.122 +/- 0.009, both measured using their charged decay modes. The measurements pro…
Measurement of the differential cross-section of highly boosted top quarks as a function of their transverse momentum ins=8 TeVproton-proton collisions using the ATLAS detector
The differential cross-section for pair production of top quarks with high transverse momentum is measured in 20.3 fb(-1) of proton-proton collisions at a center-of-mass energy of 8 TeV. The measur ...
Search for anomalous Wtb couplings in single top quark production
Made available in DSpace on 2022-04-28T20:46:40Z (GMT). No. of bitstreams: 0 Previous issue date: 2008-11-25 Science and Technology Facilities Council In 0.9fb-1 of pp̄ collisions, the D0 Collaboration presented evidence for single top quark production in events with an isolated lepton, missing transverse momentum, and two to four jets. We examine these data to study the Lorentz structure of the Wtb coupling. The standard model predicts a left-handed vector coupling at the Wtb vertex. The most general lowest dimension, CP-conserving Lagrangian admits right-handed vector and left- or right-handed tensor couplings as well. We find that the data prefer the left-handed vector coupling and set u…
Combined D0 measurements constraining theCP-violating phase and width difference in theBs0system
We combine the D0 measurement of the width difference between the light and heavy B-s(0) mass eigenstates and of the CP-violating mixing phase determined from the time-dependent angular distributions in the B-s(0)-> J/psi phi decays along with the charge asymmetry in semileptonic decays also measured with the D0 detector. With the additional constraint from the world average of the flavor-specific B-s(0) lifetime, we obtain Delta Gamma(s)equivalent to(Gamma(L)-Gamma(H))=0.13 +/- 0.09 ps(-1) and vertical bar phi(s)vertical bar=0.70(-0.47)(+0.39) or Delta Gamma(s)=-0.13 +/- 0.09 ps(-1) and vertical bar phi(s)vertical bar=2.44(-0.39)(+0.47). The data sample corresponds to an integrated luminos…
Measurement of the ratio of inclusive cross sectionsσ(pp¯→Z+b−quark jet)/σ(pp¯→Z+jet)ats=1.96 TeV
The ratio of the cross section for $p\bar{p}$ interactions producing a $Z$ boson and at least one $b$ quark jet to the inclusive $Z+{\rm jet}$ cross section is measured using $4.2\ {\rm fb}^{-1}$ of $p\bar{p}$ collisions collected with the \dzero\ detector at the Fermilab Tevatron collider at $\sqrt{s}=1.96$ TeV. The $Z\rightarrow\ell^+\ell^-$ candidate events with at least one $b$ jet are discriminated from $Z+$ charm and light jet(s) events by a novel technique that exploits the properties of the tracks associated to the jet. The measured ratio is $0.0193\pm0.0027$ for events having a jet with transverse momentum $\pt > 20 \GeV$ and pseudorapidity $|\eta| \leq 2.5$, which is the most prec…
Search for supersymmetry with gauge-mediated breaking in diphoton events at D0
We report the results of a search for supersymmetry (SUSY) with gauge-mediated breaking in the missing transverse energy distribution of inclusive diphoton events using 263 pb$^{-1}$ of data collected by the D0 experiment at the Fermilab Tevatron Collider in 2002--2004. No excess is observed above the background expected from standard model processes, and lower limits on the masses of the lightest neutralino and chargino of about 108 and 195 GeV, respectively, are set at the 95% confidence level. These are the most stringent limits to date for models with gauge-mediated SUSY breaking with a short-lived neutralino as the next-lightest SUSY particle.
Measurement of the nuclear modification factor for inclusive jets in Pb+Pb collisions at sNN=5.02 TeV with the ATLAS detector
Measurements of the yield and nuclear modification factor, R-AA, for inclusive jet production are performed using 0.49 nb(-1) of Pb+Pb data at root s(NN) = 5.02 TeV and 25 pb(-1) of Pb+Pb data at r ...
Four-fermion production in $e^+e^-$ collisions at centre-of-mass energies of 130 and 136 GeV
Four-fermion events have been selected in a data sample of 5.8 pb(-1) collected with the ALEPH detector at centre-of-mass energies of 130 and 136 GeV. The final states l(+)l(-), l(+)l(-)l(+)l(-), , and <l(+)l(-) have been examined Five events are observed in the data, in agreement with the Standard Model predictions of 6.67 +/- 0.38 events from four-fermion processes and 0.14(-0.05)(+0.19) from background processes. RI ANTONELLI, ANTONELLA/C-6238-2011; Passalacqua, Luca/F-5127-2011; Murtas, Fabrizio/B-5729-2012; Sanchez, Federico/F-5809-2012; Ferrante, Isidoro/F-1017-2012
Measurement of W-pair production in $e^+ e^-$ collisions at 189 GeV
The production of W-pairs is analysed in a data sample collected by ALEPH at a mean centre-of-mass energy of 188.6 GeV, corresponding to an integrated luminosity of 174.2 pb^-1. Cross sections are given for different topologies of W decays into leptons or hadrons. Combining all final states and assuming Standard Model branching fractions, the total W-pair cross section is measured to be 15.71 +- 0.34 (stat) +- 0.18 (syst) pb. Using also the W-pair data samples collected by ALEPH at lower centre-of-mass energies, the decay branching fraction of the W boson into hadrons is measured to be BR (W > hadrons) = 66.97 +- 0.65 (stat) +- 0.32 (syst) %, allowing a determination of the CKM matrix el…
Measurements of the charged particle multiplicity distribution in restricted rapidity intervals
Charged particle multiplicity distributions have been measured with the ALFPH detector in restricted rapidity intervals \Y\ less than or equal to 0.5, 1.0, 1.5, 2.0 along the thrust axis and also without restriction on rapidity. The distribution for the full range can be parametrized by a log-normal distribution. For smaller windows one finds a more complicated structure, which is understood to arise from perturbative effects. The negative-binomial distribution fails to describe the data both with and without the restriction on rapidity. The JETSET model is found to describe all aspects of the data while the width predicted by HERWIG is in significant disagreement.
Search for Associated Higgs Boson ProductionWH→WWW*→l±νl′±ν′+Xinpp¯Collisions ats=1.96 TeV
We present a search for associated Higgs boson production in the process $p\bar{p} \to WH\to WWW^*\to l^\pm\nu l'^\pm\nu'+X$ in final states containing two like-sign isolated electrons or muons ($e^\pm e^\pm$, $e^\pm \mu^\pm$, or $\mu^\pm \mu^\pm$). The search is based on D0 Run II data samples corresponding to integrated luminosities of 360--380 pb$^{-1}$. No excess is observed over the predicted standard model background. We set 95% C.L. upper limits on $\sigma(p\bar{p}\to WH)\times Br(H\to WW^*)$ between 3.2 and 2.8 pb for Higgs masses from 115 to 175 GeV.
Search for dark matter produced in association with a Higgs boson decaying to two bottom quarks inppcollisions ats=8 TeVwith the ATLAS detector
This article reports on a search for dark matter pair production in association with a Higgs boson decaying to a pair of bottom quarks, using data from 20.3 fb(-1) of pp collisions at a center-of-m ...
Search for excited muons inpp¯collisions ats=1.96 TeV
We present the results of a search for the production of an excited state of the muon, mu(*), in proton antiproton collisions at root s =1.96 TeV. The data have been collected with the D0 experiment at the Fermilab Tevatron Collider and correspond to an integrated luminosity of approximately 380 pb(-1). We search for mu(*) in the process p (p) over bar ->mu(*)mu, with the mu(*) subsequently decaying to a muon plus photon. No excess above the standard model expectation is observed in data. Interpreting our data in the context of a model that describes mu(*) production by four-fermion contact interactions and mu(*) decay via electroweak processes, we set a 95% confidence level production cros…
Measurement of the hadronic photon structure function at LEP 1 for 〈Q2〉 values between 9.9 and 284 GeV2
Inclusive γ*γ interactions to hadronic final states where one scattered electron or positron is detected in the electromagnetic calorimeters have been studied in the LEP 1 data taken by ALEPH from 1991 to 1995. The event sample has been used to measure the hadronic structure function of the photon F2γ in three bins with of 9.9, 20.7 and 284 GeV2.
Search for the standard model Higgs boson in tau final states
We present a search for the standard model Higgs boson using hadronically decaying tau leptons, in 1 inverse femtobarn of data collected with the D0 detector at the Fermilab Tevatron ppbar collider. We select two final states: tau plus missing transverse energy and b jets, and tau+ tau- plus jets. These final states are sensitive to a combination of associated W/Z boson plus Higgs boson, vector boson fusion and gluon-gluon fusion production processes. The observed ratio of the combined limit on the Higgs production cross section at the 95% C.L. to the standard model expectation is 29 for a Higgs boson mass of 115 GeV.
Multivariate searches for single top quark production with the D0 detector
We present a search for electroweak production of single top quarks in the s-channel (p-pbar -> t bbar + X) and t-channel (p-pbar -> tq bbar + X) modes. We have analyzed 230 pb^(-1) of data collected with the D0 detector at the Fermilab Tevatron collider at a center-of-mass energy of sqrt(s) = 1.96 TeV. Two separate analysis methods are used: neural networks and a cut-based analysis. No evidence for a single top quark signal is found. We set 95% confidence level upper limits on the production cross sections using Bayesian statistics, based on event counts and binned likelihoods formed from the neural network output. The limits from the neural network (cut-based) analysis are 6.4 pb (1…
Search for vectorlikeBquarks in events with one isolated lepton, missing transverse momentum, and jets ats=8 TeVwith the ATLAS detector
A search has been performed for pair production of heavy vectorlike down-type (B) quarks. The analysis explores the lepton-plus-jets final state, characterized by events with one isolated charged lepton (electron or muon), significant missing transverse momentum, and multiple jets. One or more jets are required to be tagged as arising from b quarks, and at least one pair of jets must be tagged as arising from the hadronic decay of an electroweak boson. The analysis uses the full data sample of pp collisions recorded in 2012 by the ATLAS detector at the LHC, operating at a center-of-mass energy of 8 TeV, corresponding to an integrated luminosity of 20.3 fb(-1). No significant excess of event…
Study of D0– mixing and D0 doubly Cabibbo-suppressed decays
Abstract Using a sample of four million hadronic Z events collected in ALEPH from 1991 to 1995, the decays D ∗+ → D 0 π s + , with D0 decaying to K−π+ or to K+π−, are studied. The relative branching ratio B(D0→K+π−)/B(D0→K−π+) is measured to be 1.84±0.59( stat. ) ±0.34( syst. ) %. The two possible contributions to the D0→K+π− decay, doubly Cabibbo-suppressed decays and D0– D 0 mixing, are disentangled by measuring the proper-time distribution of the reconstructed D0's. Assuming no interference between the two processes, the upper limit obtained on the mixing rate is 0.92% at 95% CL . The possible effect of interference between the two amplitudes is also assessed.
Electron and photon performance measurements with the ATLAS detector using the 2015-2017 LHC proton-proton collision data
This paper describes the reconstruction of electrons and photons with the ATLAS detector, employed for measurements and searches exploiting the complete LHC Run 2 dataset. An improved energy clustering algorithm is introduced, and its implications for the measurement and identification of prompt electrons and photons are discussed in detail. Corrections and calibrations that affect performance, including energy calibration, identification and isolation efficiencies, and the measurement of the charge of reconstructed electron candidates are determined using up to 81 fb−1 of proton-proton collision data collected at √s=13 TeV between 2015 and 2017.
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.
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.
Measurement of Higgs boson production in the diphoton decay channel inppcollisions at center-of-mass energies of 7 and 8 TeV with the ATLAS detector
A measurement of the production processes of the recently discovered Higgs boson is performed in the two-photon final state using 4.5 fb(-1) of proton-proton collisions data at root s = 7 TeV and 20.3 fb(-1) at root s = 8 TeV collected by the ATLAS detector at the Large Hadron Collider. The number of observed Higgs boson decays to diphotons divided by the corresponding Standard Model prediction, called the signal strength, is found to be mu = 1.17 +/- 0.27 at the value of the Higgs boson mass measured by ATLAS, m(H) = 125.4 GeV. The analysis is optimized to measure the signal strengths for individual Higgs boson production processes at this value of m(H). They are found to be mu(ggF) = 1.32…
Fermion pair production in e+e- collisions at 189-209 GeV and constraints on physics beyond the Standard Model
Cross sections, angular distributions and forward-backward asymmetries are presented, of two-fermion events produced in e+e- collisions at centre-of-mass energies from 189 to 209 GeV at LEP, measured with the ALEPH detector. Results for e+e-, mu+mu-, tau+tau-, qq, bb and cc production are in agreement with the Standard Model predictions. Constraints are set on scenarios of new physics such as four-fermion contact interactions, leptoquarks, Z' bosons, TeV-scale quantum gravity and R-parity violating squarks and sneutrinos.
The upgraded DO detector
The DØ experiment enjoyed a very successful data-collection run at the Fermilab Tevatron collider between 1992 and 1996. Since then, the detector has been upgraded to take advantage of improvements to the Tevatron and to enhance its physics capabilities. We describe the new elements of the detector, including the silicon microstrip tracker, central fiber tracker, solenoidal magnet, preshower detectors, forward muon detector, and forward proton detector. The uranium/liquid-argon calorimeters and central muon detector, remaining from Run I, are discussed briefly. We also present the associated electronics, triggering, and data acquisition systems, along with the design and implementation of s…
Measurement of the top quark mass in thelepton+jetsfinal state with the matrix element method
We present a measurement of the top quark mass with the Matrix Element method in the lepton+jets final state. As the energy scale for calorimeter jets represents the dominant source of systematic uncertainty, the Matrix Element likelihood is extended by an additional parameter, which is defined as a global multiplicative factor applied to the standard energy scale. The top quark mass is obtained from a fit that yields the combined statistical and systematic jet energy scale uncertainty.
Study ofZγEvents and Limits on AnomalousZZγandZγγCouplings inpp¯Collisions ats=1.96 TeV
We present a measurement of the Z gamma production cross section and limits on anomalous ZZ gamma and Z gamma gamma couplings for form-factor scales of Lambda=750 and 1000 GeV. The measurement is based on 138 (152) candidates in the ee gamma (mu mu gamma) final state using 320(290) pb(-1) of p (p) over bar collisions at root s=1.96 TeV. The 95% C.L. limits on real and imaginary parts of individual anomalous couplings are vertical bar h(10,30)(Z)vertical bar < 0.23, vertical bar h(20,40)(Z)vertical bar < 0.020, vertical bar h(10,30)(gamma)vertical bar < 0.23, and vertical bar h(20,40)(gamma)vertical bar < 0.019 for Lambda=1000 GeV.
Measurements of the top quark branching ratios into channels with leptons and quarks with the ATLAS detector
Measurements of the branching ratios of top quark decays into leptons and jets using events with t[bar over t] (top antitop) pairs are reported. Events were recorded with the ATLAS detector at the LHC in pp collisions at a center-of-mass energy of 7 TeV. The collected data sample corresponds to an integrated luminosity of 4.6 fb[superscript −1]. The measured top quark branching ratios agree with the Standard Model predictions within the measurement uncertainties of a few percent.
Measurement of the charge asymmetry in semileptonic Bs0 decays.
Made available in DSpace on 2022-04-28T20:16:10Z (GMT). No. of bitstreams: 0 Previous issue date: 2007-04-11 We have performed the first direct measurement of the time-integrated flavor untagged charge asymmetry in semileptonic Bs0 decays ASLs,unt by comparing the decay rate of Bs0→μ+Ds-νX, where Ds- π- and →K+K-, with the charge-conjugate B̄s0 decay rate. This sample was selected from 1.3fb-1 of data collected by the D0 experiment in run II of the Fermilab Tevatron collider. We obtain ASLs,unt=[1.23±0.97(stat)±0. 17(syst)]×10-2. Assuming that Δms/Γ̄s 1, this result can be translated into a measurement of the CP-violating phase in Bs0 mixing: ΔΓs/Δmstan s=[2.45±1.93(stat)±0.35(syst)] ×10-2.…
Measurement of hard double-parton interactions inW(???) + 2-jet events at $\sqrt{s}\,=7$ TeV with the ATLAS detector
The production of W bosons in association with two jets in proton–proton collisions at a centre-of-mass energy of √s=7 TeV has been analysed for the presence of double-parton interactions using data corresponding to an integrated luminosity of 36 pb[superscript −1], collected with the ATLAS detector at the Large Hadron Collider. The fraction of events arising from double-parton interactions, f[superscript (D) over subscript DP], has been measured through the p[subscript T] balance between the two jets and amounts to f[superscript (D) over subscript DP] = 0.08 ± 0.01 (stat.) ± 0.02 (sys.) for jets with transverse momentum p[subscript T] > 20 GeV and rapidity |y| < 2.8. This corresponds to a …
Search for supersymmetry via associated production of charginos and neutralinos in final states with three leptons
A search for associated production of charginos and neutralinos is performed using data recorded with the D0 detector at a ppbar center-of-mass energy of 1.96 TeV at the Fermilab Tevatron Collider. This analysis considers final states with missing transverse energy and three leptons, of which at least two are electrons or muons. No evidence for supersymmetry is found in a dataset corresponding to an integrated luminosity of 320 pb-1. Limits on the product of the production cross section and leptonic branching fraction are set. For the minimal supergravity model, a chargino lower mass limit of 117 GeV at the 95% C.L. is derived in regions of parameter space with enhanced leptonic branching f…
Measurements of spin correlation in top-antitop quark events from proton-proton collisions ats=7 TeVusing the ATLAS detector
Measurements of spin correlation in top quark pair production are presented using data collected with the ATLAS detector at the LHC with proton-proton collisions at a center-of-mass energy of 7 TeV, corresponding to an integrated luminosity of 4.6 fb(-1). Events are selected in final states with two charged leptons and at least two jets and in final states with one charged lepton and at least four jets. Four different observables sensitive to different properties of the top quark pair production mechanism are used to extract the correlation between the top and antitop quark spins. Some of these observables are measured for the first time. The measurements are in good agreement with the Stan…
Search for direct stau production in events with two hadronic τ -leptons in s=13 TeV pp collisions with the ATLAS detector
A search for the direct production of the supersymmetric partners of τ -leptons (staus) in final states with two hadronically decaying τ -leptons is presented. The analysis uses a dataset of p p collisions corresponding to an integrated luminosity of 139 fb − 1 , recorded with the ATLAS detector at the Large Hadron Collider at a center-of-mass energy of 13 TeV. No significant deviation from the expected Standard Model background is observed. Limits are derived in scenarios of direct production of stau pairs with each stau decaying into the stable lightest neutralino and one τ -lepton in simplified models where the two stau mass eigenstates are degenerate. Stau masses from 120 GeV to 390…
Search for the Standard Model Higgs Boson in the Missing Energy and Acoplanarb-Jet Topology ats=1.96 TeV
We report a search for the standard model Higgs boson in the missing energy and acoplanar b-jet topology, using an integrated luminosity of 0.93 fb(-1) recorded by the D0 detector at the Fermilab Tevatron p (p) over bar Collider. The analysis includes signal contributions from p (p) over bar -> ZH -> v (v) over barb (b) over bar, as well as from WH production in which the charged lepton from the W boson decay is undetected. Neural networks are used to separate signal from background. In the absence of a signal, we set limits on sigma(p (p) over bar -> VH) x B(H -> b (b) over bar) at the 95% C.L. of 2.6-2.3 pb, for Higgs boson masses in the range 105-135 GeV, where V W, Z. The corresponding …
Improved search for $B_{s}^{0} - \overline{B}_{s}^{0}$ oscillations
An improved search for Bs oscillations is performed in the ALEPH data sample collected during the first phase of LEP, and reprocessed in 1998. Three analyses based on complementary event selections are presented. First, decays of Bs mesons into hadronic flavour eigenstates are fully reconstructed. This selection yields a small sample of candidates with excellent decay length and momentum resolution and high average Bs purity. Semileptonic decays with a reconstructed Ds- meson provide a second sample with larger statistics, high average Bs purity, but a poorer momentum and decay length resolution due to the partial decay reconstruction. Finally, semileptonic b-hadron decays are inclusively s…
Search for charged Higgs bosons in $e^+ e^-$ collisions at energies up to $\sqrt{s}$ = 189 GeV
The data collected at centre-of-mass energies of 188.6 GeV by ALEPH at LEP, corresponding to an integrated luminosity of 176.2 pb-1, are analysed in a search for pair-produced charged Higgs bosons H+/-. Three analyses are employed to select the taunutaunu, taunucs and cscs final states. No evidence for a signal is found. Upper limits are set on the production cross section as a function of the branching fraction BR(H+ to tau nu) and of the mass M(H+), assuming that the sum of the branching ratios is equal to one. In the framework of a two-Higgs-doublet model, charged Higgs bosons with masses below 65.4 GeV/c2 are excluded at 95% confidence level independently of the decay mode.
Search for Neutral Higgs Bosons in Multi-b-Jet Events inpp¯Collisions ats=1.96 TeV
Data recorded by the D0 experiment at the Fermilab Tevatron Collider are analyzed to search for neutral Higgs bosons produced in association with b quarks. This production mode can be enhanced in the minimal supersymmetric standard model (MSSM). The search is performed in the three b quark channel using multijet triggered events corresponding to an integrated luminosity of 1 fb(-1). No statistically significant excess of events with respect to the predicted background is observed and limits are set in the MSSM parameter space.
Search for a Heavy Neutral Particle Decaying toeμ,eτ, orμτinppCollisions ats=8 TeVwith the ATLAS Detector
This Letter presents a search for a heavy neutral particle decaying into an opposite-sign different-flavor dilepton pair, e(+/-) mu(-/+), e(+/-) tau(-/+), or mu(+/-) tau(-/+) using 20.3 fb(-1) of pp collision data at root s = 8 TeV collected by the ATLAS detector at the LHC. The numbers of observed candidate events are compatible with the standard model expectations. Limits are set on the cross section of new phenomena in two scenarios: the production of (nu) over tilde (tau) in R-parity-violating supersymmetric models and the production of a lepton-flavor-violating Z' vector boson.
Measurement of the W±Z production cross section and limits on anomalous triple gauge couplings in proton–proton collisions at s=7 TeV with the ATLAS detector
This Letter presents a measurement of W(+/-)Z production in 1.02 fb(-1) of pp collision data at root s = 7 TeV collected by the ATLAS experiment in 2011. Doubly leptonic decay events are selected w ...
First measurement of the quark-to-photon fragmentation function
Earlier measurements at LEP of isolated hard photons in hadronic Z decays, attributed to radiation from primary quark pairs, have been extended in the ALEPH experiment to include hard photon production inside hadron jets. Events are selected where all particles combine democratically to form hadron jets, one of which contains a photon with a fractional energy z greater than or equal to 0.7. After statistical subtraction of non-prompt photons, the quark-to-photon fragmentation function, D(z), is extracted directly from the measured 2-jet rate. By taking into account the perturbative contributions to D(z) obtained from an O(alpha alpha(s)) QCD calculation, the unknown non-perturbative compone…
Production of orbitally excited charm mesons in semileptonic B decays
A sample of 3.6 million hadronic Z decays recorded between 1991 and 1995 with the ALEPH detector at LEP is used to investigate semileptonic decays of B mesons into final states involving orbitally excited charm mesons. Topological vertex criteria are used to search for decays involving narrow D** states as well as wide D** resonances and non-resonant D(*)pi final states. The sum of the branching ratios for these processes is measured to be Br((B) over bar --> D pi l(-)(v) over bar) + Br((B) over bar --> D*pi l(-)(v) over bar) = (2.26 +/-t 0.29(stat) +/- 0.33(syst))%, which accounts for a significant fraction of the deficit between inclusive measurements and the sum of exclusive semileptonic…
Direct limits on the $B_s^0$ oscillation frequency
Made available in DSpace on 2022-04-28T20:09:59Z (GMT). No. of bitstreams: 0 Previous issue date: 2006-01-01 We report results of a study of the Bs0 oscillation frequency using a large sample of Bs0 semileptonic decays corresponding to approximately 1fb-1 of integrated luminosity collected by the D0 experiment at the Fermilab Tevatron Collider in 2002-2006. The amplitude method gives a lower limit on the Bs0 oscillation frequency at 14.8ps-1 at the 95% C.L. At Δms=19ps-1, the amplitude deviates from the hypothesis A=0 (1) by 2.5 (1.6) standard deviations, corresponding to a two-sided C.L. of 1% (10%). A likelihood scan over the oscillation frequency, Δms, gives a most probable value of 19ps…
Measurement of the Ratio ofB+andB0Meson Lifetimes
The ratio of the B+ and B-0 meson lifetimes was measured using data collected in 2002-2004 by the D0 experiment in Run II of the Fermilab Tevatron Collider. These mesons were reconstructed in BRμ(+)ν D*-X decays, which are dominated by B-0 and BRμ(+)ν(D) over bar X-0 decays, which are dominated by B+. The ratio of lifetimes is measured to be τ(+)/τ(0)=1.080P 0.016(stat)P 0.014(syst).
Search for squarks and gluinos in final states with hadronically decaying τ -leptons, jets, and missing transverse momentum using pp collisions at s=13 TeV with the ATLAS detector
A search for supersymmetry in events with large missing transverse momentum, jets, and at least one hadronically decaying τ-lepton is presented. Two exclusive final states with either exactly one or at least two τ-leptons are considered. The analysis is based on proton-proton collisions at s=13 TeV corresponding to an integrated luminosity of 36.1 fb-1 delivered by the Large Hadron Collider and recorded by the ATLAS detector in 2015 and 2016. No significant excess is observed over the Standard Model expectation. At 95% confidence level, model-independent upper limits on the cross section are set and exclusion limits are provided for two signal scenarios: a simplified model of gluino pair pr…
Search for a scalar top almost degenerate with the lightest neutralino e(+)e(-) collisions at root s up to 202 GeV
Data collected at centre-of-mass energies from 189 GeV to 202 GeV by the ALEPH detector at LEP corresponding to an integrated luminosity of 411 pb(-1), are analysed in a search for the scalar top in the decay channels (t) over tilde --> c/u chi for small mass differences between the stop and the lightest neutralino. No evidence for deviations from the Standard Model expectation is found and a lower limit of 59 GeV/c(2) is set for the stop mass, independent of the stop to neutralino mass difference and of the stop lifetime. (C) 2000 Elsevier Science B.V. All rights reserved.
Determination of the strong coupling constant from the inclusive jet cross section inpp¯collisions ats=1.96 TeV
We determine the strong coupling constant alpha(s) and its energy dependence from the p(T) dependence of the inclusive jet cross section in pp collisions at s=1.96 TeV. The strong coupling constant is determined over the transverse momentum range 50 < p(T)< 145 GeV. Using perturbative QCD calculations to order O(alpha(3)(s)) combined with O(alpha(4)(s)) contributions from threshold corrections, we obtain alpha(s)(M-Z)=0.1161(-0.0048)(+0.0041). This is the most precise result obtained at a hadron-hadron collider.
Search for pair production of second generation scalar leptoquarks in pp¯ collisions at s=1.96 TeV
We report on a search for the pair production of second generation scalar leptoquarks (LQ_2) in ppbar collisions at the center-of-mass energy sqrt(s) = 1.96 TeV, using data corresponding to an integrated luminosity of 294 +- 19 pb^-1 recorded with the D0 detector. No evidence for a leptoquark signal in the LQ_2 LQ_2 -> muq muq channel has been observed, and upper bounds on the product of cross section times branching fraction were set. This yields lower mass limits of m(LQ_2) > 247 GeV for beta = Br(LQ_2->muq) = 1 and m(LQ_2) > 182 GeV for beta = 1/2. Combining these limits with previous D0 results, the lower limits on the mass of a second generation scalar leptoquark are m(LQ_2) > 251 GeV …
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 scalar leptoquarks in pp collisions at $\sqrt{s}$=13 TeV with the ATLAS experiment
An inclusive search for a new-physics signature of lepton-jet resonances has been performed by the ATLAS experiment. Scalar leptoquarks, pair-produced in pp collisions at s √s = 13 TeV at the large hadron collider, have been considered. An integrated luminosity of 3.2 fb-1, corresponding to the full 2015 dataset was used. First (second) generation leptoquarks were sought in events with two electrons (muons) and two or more jets. The observed event yield in each channel is consistent with Standard Model background expectations. The observed (expected) lower limits on the leptoquark mass at 95% confidence level are 1100 and 1050 GeV (1160 and 1040 GeV) for first and second generation leptoqua…
Search for excited electrons inpp¯collisions ats=1.96 TeV
We present the results of a search for the production of an excited state of the electron, e(*), in proton-antiproton collisions at root s = 1.96 TeV. The data were collected with the D0 experiment at the Fermilab Tevatron Collider and correspond to an integrated luminosity of approximately 1 fb(-1). We search for e(*) in the process p (p) over bar -> e(*)e, with the e(*) subsequently decaying to an electron plus photon. No excess above the standard model background is observed. Interpreting our data in the context of a model that describes e(*) production by four-fermion contact interactions and e(*) decay via electroweak processes, we set 95% C.L. upper limits on the production cross sect…
Improved measurement of theB 0 andB + meson lifetimes
The lifetimes of the B 0 and B + mesons have been measured with the Aleph detector at LEP, using approximately 3 million hadronic Z decays collected in the period 1991 1994. In the first of three methods, semileptonic decays of B 0 and B + mesons were partially reconstructed by identifying events containing a lepton with an associated D*- orbar D^0 meson. The second method used fully reconstructed B 0 and B + mesons. The third method, used to measure the B 0 lifetime, employed a partial reconstruction technique to identify B 0→ D*- π + X decays. The combined results are begin{gathered} tau _0 = 1.55 ± 0.06 ± 0.03 ps, \ tau _ + = 1.58 ± 0.09 ± 0.03 ps, \ tfrac{{tau _ + }}{{tau _0 }} = 1.03 ±…
Search for the Standard Model Higgs Boson in thepp¯→ZH→νν¯bb¯Channel
We report a search for the standard model (SM) Higgs boson based on data collected by the D0 experiment at the Fermilab Tevatron Collider, corresponding to an integrated luminosity of 260 pb^-1. We study events with missing transverse energy and two acoplanar b-jets, which provide sensitivity to the ZH production cross section in the neutrino-neutrino-b-b channel and to WH production, when the lepton from the W -> lepton+neutrino decay is undetected. The data are consistent with the SM background expectation, and we set 95% C.L. upper limits on sigma(p p-bar -> ZH/WH) x B(H -> b b-bar) from 3.4/8.3 to 2.5/6.3 pb, for Higgs masses between 105 and 135 GeV.
Search for Production of Single Top Quarks ViatcgandtugFlavor-Changing-Neutral-Current Couplings
We search for the production of single top quarks via flavor-changing neutral current couplings of a gluon to the top quark and a charm ($c$) or up ($u$) quark. We analyze 230 pb$^{-1}$ of lepton + jets data from $\ppbar$ collisions at a center of mass energy of 1.96 TeV collected by the D0 detector at the Fermilab Tevatron Collider. We observe no significant deviation from standard model predictions, and hence set upper limits on the anomalous coupling parameters $\kappacLambda$ and $\kappauLambda$, where $\kappag$ define the strength of $tcg$ and $tug$ couplings, and $\Lambda$ defines the scale of new physics. The limits at 95% C.L. are: $\kappacLambda < 0.15 \rm TeV^{-1}$ and $\kappauLam…
Search for squarks and gluinos in events with jets and missing transverse energy in pp¯ collisions at s=1.96 TeV
Abstract The results of a search for squarks and gluinos using data from p p ¯ collisions recorded at a center-of-mass energy of 1.96 TeV by the DO detector at the Fermilab Tevatron Collider are reported. The topologies analyzed consist of acoplanar-jet and multijet events with large missing transverse energy. No evidence for the production of squarks or gluinos was found in a data sample of 310 pb−1. Lower limits of 325 and 241 GeV were derived at the 95% C.L. on the squark and gluino masses, respectively, within the framework of minimal supergravity with tan β = 3 , A 0 = 0 , and μ 0 .
Production of excited beauty states in Z decays
A data sample of about 3.0 million hadronicZ decays collected by the ALEPH experiment at LEP in the years 1991 through 1994 is used to make an inclusive selection of B hadron events. In this event sample 4227±140±252B* mesons in the decayB*→Bγ and 1944±108±161B** u,d mesons decaying into a B meson and a charged pion are reconstructed. Here and in the followingB** u,d denotes the eightL=1(bū) and (bd) states and their charge conjugate. For the well establishedB* meson the following quantities are obtained:ΔM=M B*−MB=(45.30±0.35±0.87) MeV/c2 andN B*/(N B+N B*)=(77.1±2.6±7.0)%. The angular distribution of the photons in theB* rest frame is used to measure the relative contribution of longitudi…
Evidence for production of single top quarks
We present first evidence for the production of single top quarks in the D0 detector at the Fermilab Tevatron ppbar collider. The standard model predicts that the electroweak interaction can produce a top quark together with an antibottom quark or light quark, without the antiparticle top quark partner that is always produced from strong coupling processes. Top quarks were first observed in pair production in 1995, and since then, single top quark production has been searched for in ever larger datasets. In this analysis, we select events from a 0.9 fb-1 dataset that have an electron or muon and missing transverse energy from the decay of a W boson from the top quark decay, and two, three, …
Measurement of thepp¯→WZ+Xcross section ats=1.96 TeVand limits onWWZtrilinear gauge couplings
We present measurements of the process p (P) over bar -> WZ + X -> l 'nu(l ')l (l) over bar at root s = 1:96 TeV,where l and l ' are electrons or muons. Using 1 fb(-1) of data from the D0 experiment, we observe 13 candidates with an expected background of 4.5 +/- 0.6 events and measure a cross section sigma(WZ) = 2.7(-1.3)(+1.7) pb. From the number of observed events and the Z boson transverse momentum distribution, we limit the trilinear WWZ gauge couplings to -0: 17 <= lambda(Z) <= 0.21 (Delta k(Z) <= 0.29(lambda(Z) = 0) at the 95% C.L. for a form factor scale Lambda = 2 TeV. Further, assuming that Delta g(1)(Z) = Delta k(Z), we find -0.12 <= Delta k(Z) <= 0.29(lambda(Z) = 0) at the 95% C…
Measurement of thepp¯→Wγ+Xcross section ats=1.96 TeV andWWγanomalous coupling limits
The WWgamma triple gauge boson coupling parameters are studied using p-pbar -> l nu gamma + X (l = e,mu) events at sqrt(s) = 1.96 TeV. The data were collected with the DO detector from an integrated luminosity of 162 pb^{-1} delivered by the Fermilab Tevatron Collider. The cross section times branching fraction for p-pbar -> W(gamma) + X -> l nu gamma + X with E_T^{gamma} > 8 GeV and Delta R_{l gamma} > 0.7 is 14.8 +/- 1.6 (stat) +/- 1.0 (syst) +/- 1.0 (lum) pb. The one-dimensional 95% confidence level limits on anomalous couplings are -0.88 < Delta kappa_{gamma} < 0.96 and -0.20 < lambda_{gamma} < 0.20.
Observation and Properties of theX(3872)Decaying toJ/ψπ+π−inpp¯Collisions ats=1.96 TeV
We report the observation of the X(3872) in the J/psipi(+)pi(-) channel, with J/psi decaying to mu(+)mu(-), in p (p) over bar collisions at roots=1.96 TeV. Using approximately 230 pb(-1) of data collected with the Run II D0 detector, we observe 522+/-100 X(3872) candidates. The mass difference between the X(3872) state and the J/psi is measured to be 774.9+/-3.1(stat)+/-3.0(syst) MeV/c(2). We have investigated the production and decay characteristics of the X(3872) and find them to be similar to those of the psi(2S) state.
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…
Determination of sin^2(theta(eff)(w)) using jet charge measurements in hadronic Z decays
The electroweak mixing angle is determined with high precision from measurements of the mean difference between forward and backward hemisphere charges in hadronic decays of the Z. A data sample of 2.5 million hadronic Z decays recorded over the period 1990 to 1994 in the ALEPH detector at LEP is used. The mean charge separation between event hemispheres containing the original quark and antiquark is measured for b (b) over bar and c (c) over bar events in subsamples selected by their long lifetimes or using fast D*'s. The corresponding average charge separation for light quarks is measured in an inclusive sample from the anticorrelation between charges of opposite hemispheres and agrees wi…
Direct Observation of the StrangebBaryonΞb−
We report the first direct observation of the strange b baryon Xi(b)- (Xi(b)+). We reconstruct the decay Xi(b)- -->J/psiXi-, with J/psi-->mu+mu-, and Xi--->Lambdapi--->ppi-pi- in pp collisions at square root of s =1.96 TeV. Using 1.3 fb(-1) of data collected by the D0 detector, we observe 15.2 +/- 4.4(stat)(-0.4)(+1.9)(syst) Xi(b)- candidates at a mass of 5.774 +/- 0.011(stat) +/- 0.015(syst) GeV. The significance of the observed signal is 5.5 sigma, equivalent to a probability of 3.3 x 10(-8) of it arising from a background fluctuation. Normalizing to the decay Lambda(b)-->J/psiLambda, we measure the relative rate sigma(Xi(b-) x B(Xi)b})- -->J/psiXi-)/sigma(Lambda(b)) x B(Lambda(b)-->J/psi…
Measurement of top quark pair differential cross sections in the dilepton channel in pp collisions at s=7 and 8 TeV with ATLAS
Measurements of normalized differential cross-sections of top quark pair ($t\bar t$) production are presented as a function of the mass, the transverse momentum and the rapidity of the $t\bar t$ system in proton-proton collisions at center-of-mass energies of $\sqrt{s}$ = 7 TeV and 8 TeV. The dataset corresponds to an integrated luminosity of 4.6 fb$^{-1}$ at 7 TeV and 20.2 fb$^{-1}$ at 8 TeV, recorded with the ATLAS detector at the Large Hadron Collider. Events with top quark pair signatures are selected in the dilepton final state, requiring exactly two charged leptons and at least two jets with at least one of the jets identified as likely to contain a $b$-hadron. The measured distributi…
Measurement of the Shape of the Boson-Transverse Momentum Distribution inpp¯→Z/γ*→e+e−+XEvents Produced ats=1.96 TeV
We present a measurement of the shape of the Z/gamma* boson transverse momentum (q(T)) distribution in p (p) over bar -> Z/gamma(*)-> e(+)e(-)+X events at a center-of-mass energy of 1.96 TeV using 0.98 fb(-1) of data collected with the D0 detector at the Fermilab Tevatron collider. The data are found to be consistent with the resummation prediction at low q(T), but above the perturbative QCD calculation in the region of q(T)> 30 GeV/c. Using events with q(T)< 30 GeV/c, we extract the value of g(2), one of the nonperturbative parameters for the resummation calculation. Data at large boson rapidity y are compared with the prediction of resummation and with alternative models that employ a res…
Search for Pair Production of Doubly Charged Higgs Bosons in theH++H--→μ+μ+μ−μ−Final State
We report the results of a search for pair production of doubly-charged Higgs bosons via ppbar to H^{++}H^{--}X to mu^+mu^+mu^-mu^-X at sqrt{s} = 1.96 TeV. We use a dataset corresponding to an integrated luminosity of 1.1 fb^{-1} collected from 2002 to 2006 by the D0 detector at the Fermilab Tevatron Collider. In the absence of an excess above the standard model background, lower mass limits of M(H^{pmpm}_L) > 150 GeV/c^2 and M(H^{pmpm}_R) > 127 GeV/c^2 at 95% C.L. are set, respectively, for left-handed and right-handed doubly-charged Higgs bosons assuming a 100% branching ratio into muons.
Search for Decay of a Fermiophobic Higgs Bosonhf→γγwith the D0 Detector ats=1.96 TeV
We report the results of a search for a narrow resonance decaying into two photons in 1.1 fb(-1) of data collected by the D0 experiment at the Fermilab Tevatron Collider during the period 2002-2006. We find no evidence for such a resonance and set a lower limit on the mass of a fermiophobic Higgs boson of m(hf) > 100 GeV at the 95% C.L. This exclusion limit exceeds those obtained in previous searches at the Fermilab Tevatron and covers a significant region of the parameter space B(h(f) -> gamma gamma) vs m(hf) which was not accessible at the CERN Large Electron-Positron Collider.
Measurement of upsilon production in 7 TeV pp collisions at ATLAS
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
Production ofWZEvents inpp¯Collisions ats=1.96 TeVand Limits on AnomalousWWZCouplings
We present results from a search for WZ production with subsequent decay to l nu l'(l) over bar'(l and l' = e or mu) using 0.30 fb(-1) of data collected by the D0 experiment between 2002 and 2004 at the Fermilab Tevatron. Three events with WZ decay characteristics are observed. With an estimated background of 0.71 +/- 0.08 events, we measure the WZ production cross section to be 4.5(-2.6)(+3.8) pb, with a 95% C.L. upper limit of 13.3 pb. The 95% C.L. limits for anomalous WWZ couplings are found to be -2.0 <Delta kappa(Z)< 2.4 for form factor scale Lambda=1 TeV, and -0.48 <lambda(Z)< 0.48 and -0.49 <Delta g(1)(Z)< 0.66 for Lambda=1.5 TeV.
Search for Scalar Neutrino Superpartners ine+μFinal States inpp¯Collisions ats=1.96 TeV
We report a search for R-parity-violating production and decay of sneutrino particles in the e mu final state with 1.04 +/- 0.06 fb(-1) of data collected with the D-0 detector at the Fermilab Tevatron Collider in 2002-2006. Good agreement between the data and the standard model prediction is observed. With no evidence for new physics, we set limits on the R-parity-violating couplings lambda'(311) and lambda(312) as a function of the sneutrino mass.
Combination of Searches for Invisible Higgs Boson Decays with the ATLAS Experiment
Dark matter particles, if sufficiently light, may be produced in decays of the Higgs boson. This Letter presents a statistical combination of searches for H → invisible decays where H is produced according to the standard model via vector boson fusion, Z(ℓℓ)H, and W/Z(had)H, all performed with the ATLAS detector using 36.1 fb⁻¹ of pp collisions at a center-of-mass energy of √s = 13 TeV at the LHC. In combination with the results at √s = 7 and 8 TeV, an exclusion limit on the H → invisible branching ratio of 0.26(0.17-0.05+0.07) at 95% confidence level is observed (expected).
Combination oftt¯cross section measurements and constraints on the mass of the top quark and its decays into charged Higgs bosons
We combine measurements of the top quark pair production cross section in p (p) over bar collisions in the l + jets, ll, and tau l final states ( where l is an electron or muon) at a center of mass energy of root s = 1.96 TeV in 1 fb(-1) of data collected with the D0 detector. For a top quark mass of 170 GeV/c(2), we obtain sigma(t (t) over bar) = 8.18(-0.87)(+0.98) pb in agreement with the theoretical prediction. Based on predictions from higher order quantum chromodynamics, we extract a mass for the top quark from the combined t (t) over bar cross section, consistent with the world average of the top quark mass. In addition, the ratios of t (t) over bar cross sections in different final s…
Search for anomalous heavy-flavor quark production in association with W bosons.
We present a search for anomalous production of heavy-flavor quark jets in association with a W boson at the Fermilab Tevatron ppbar Collider. This search is conducted through an examination of the exclusive jet spectrum of W+jets final states in which the heavy-flavor quark content has been enhanced by requiring at least one tagged jet in an event. Jets are tagged by the combined use of two algorithms, one based on semileptonic decays of b/c hadrons, and the other on their lifetimes. We compare data in e+jets (164 pb-1) and mu+jets (145 pb-1) channels, collected with the D0 detector at sqrt{s}=1.96 TeV, to expectations from the standard model, and set upper limits on anomalous production o…
Search for third generation scalar leptoquarks decaying into tau b
We have searched for third generation leptoquarks (LQ3) using 1.05 inverse femtobarns of data collected with the D0 detector at the Fermilab Tevatron Collider operating at sqrt(s)=1.96 TeV. We set a 95% C.L. lower limit of 210 GeV on the mass of a scalar LQ3 state decaying solely to a b quark and a tau lepton.
Evidence for the production of three massive vector bosons with the ATLAS detector
A search for the production of three massive vector bosons in proton–proton collisions is performed using data at TeV recorded with the ATLAS detector at the Large Hadron Collider in the years 2015–2017, corresponding to an integrated luminosity of 79.8 fb−1. Events with two same-sign leptons ℓ (electrons or muons) and at least two reconstructed jets are selected to search for . Events with three leptons without any same-flavour opposite-sign lepton pairs are used to search for , while events with three leptons and at least one same-flavour opposite-sign lepton pair and one or more reconstructed jets are used to search for . Finally, events with four leptons are analysed to search for and .…
B-physics results from LEP
Abstract The LEP collider continues to improve our knowledge and understanding of B-physics. Recent results are presented in the areas of B-hadron lifetimes, BB oscillations, B-spectroscopy and rare B-decays.
Search for pentaquarks states in Z decays
Exotic hadrons made of five quarks (pentaquarks) are searched for in hadronic Z decays collected by the ALEPH detector at LEP. No significant signal is observed. At 95% C.L. upper limits are set on the production rates N of such particles and their charge-conjugate state per Z decay: N Θ(1535)+·BR(Θ(1535)+→pK S0)<6.2×10-4, N Ε(1862)-·BR(Ε(1862)-→Ε -π-)<4.5×10-4, N Ε(1862)0·BR(Ε(1862)0→Ε -π+)<8.9×10-4, N Θc(3100)0·BR(Θc(3100) 0→D*-p)<6.3×10-4, N Θc(3100)0·BR(Θc(3100) 0→D-p)<31×10-4. © 2004 Elsevier B.V. All rights reserved.
Inclusive production of neutral pions in hadronic Z decays
A measurement of the inclusive production of pi(0) mesons in hadronic Z decays is presented and compared to Monte Carlo model predictions. The analysis is based on approximately 2 million hadronic events recorded with the ALEPH detector at LEP at a centre-of-mass energy of root s = 91.2 GeV. Neutral pions are reconstructed using photons measured in the electromagnetic calorimeter and photons from conversion pairs. The inclusive pi(0) momentum spectrum is measured in the range 0.025 < x(p) = p/p(beam) < 1. In this range the number of pi(0) per hadronic Z is found to be 4.80 +/- 0.07(stat) +/- 0.31(sys). The differential inclusive pi(0) cross section is also measured as a function of transver…
Lifetime Difference andCP-Violating Phase in theBs0System
From an analysis of the decay B-s(0)-> J/psi phi, we obtain the width difference between the light and heavy mass eigenstates Delta Gamma equivalent to(Gamma(L)-Gamma(H))=0.17 +/- 0.09(stat)+/- 0.02(syst) ps(-1) and the CP-violating phase phi(s)=-0.79 +/- 0.56(stat)(-0.01)(+0.14)(syst). Under the hypothesis of no CP violation (phi(s)equivalent to 0), we obtain 1/Gamma=tau/(B-s(0))=1.52 +/- 0.08(stat)(-0.03)(+0.01)(syst) ps and Delta Gamma=0.12(-0.10)(+0.08)(stat)+/- 0.02(syst) ps(-1). The data sample corresponds to an integrated luminosity of about 1.1 fb(-1) accumulated with the D0 detector at the Fermilab Tevatron collider. This is the first direct measurement of the CP-violating mixing p…
Search for a heavy charged boson in events with a charged lepton and missing transverse momentum from pp collisions at s=13 TeV with the ATLAS detector
A search for a heavy charged-boson resonance decaying into a charged lepton (electron or muon) and a neutrino is reported. A data sample of 139 fb−1 of proton-proton collisions at √s=13 TeV collected with the ATLAS detector at the LHC during 2015–2018 is used in the search. The observed transverse mass distribution computed from the lepton and missing transverse momenta is consistent with the distribution expected from the Standard Model, and upper limits on the cross section for pp→W′→lν are extracted (l=e or μ). These vary between 1.3 pb and 0.05 fb depending on the resonance mass in the range between 0.15 and 7.0 TeV at 95% confidence level for the electron and muon channels combined. …
Search for sleptons in e(+)e(-) collisions at centre-of-mass energies up to 184 GeV
The data collected by the ALEPH experiment at LEP at centre-of-mass energies around 183 GeV are analysed to search for sleptons, the partners of leptons in supersymmetric theories. The previously published search for acoplanar leptons and missing energy has been updated. New searches have been developed to cover a wider range of slepton signals. These include single electrons, acoplanar leptons accompanied by two photons plus missing energy as well as particles with lifetime. No evidence for the production of any such particles is found. Slepton mass limits are reported within gravity mediated and gauge mediated SUSY breaking scenarios. (C) 1998 Elsevier Science B.V. All rights reserved.
Search for Supersymmetry inppCollisions ats=7 TeVin Events with Two Photons and Missing Transverse Energy
A search for supersymmetry in the context of general gauge-mediated breaking with the lightest neutralino as the next-to-lightest supersymmetric particle and the gravitino as the lightest is presented. The data sample corresponds to an integrated luminosity of 36 pb(-1) recorded by the CMS experiment at the LHC. The search is performed by using events containing two or more isolated photons, at least one hadronic jet, and significant missing transverse energy. No excess of events at high missing transverse energy is observed. Upper limits on the signal cross section for general gauge-mediated supersymmetry between 0.3 and 1.1 pb at the 95% confidence level are determined for a range of squa…
Observation of a Centrality-Dependent Dijet Asymmetry in Lead-Lead Collisions atsNN=2.76 TeVwith the ATLAS Detector at the LHC
By using the ATLAS detector, observations have been made of a centrality-dependent dijet asymmetry in the collisions of lead ions at the Large Hadron Collider. In a sample of lead-lead events with a per-nucleon center of mass energy of 2.76 TeV, selected with a minimum bias trigger, jets are reconstructed in fine-grained, longitudinally segmented electromagnetic and hadronic calorimeters. The transverse energies of dijets in opposite hemispheres are observed to become systematically more unbalanced with increasing event centrality leading to a large number of events which contain highly asymmetric dijets. This is the first observation of an enhancement of events with such large dijet asymme…
Measurement of triple gauge-boson couplings at 172 GeV
The triple gauge-boson couplings, αWΦ, αW and αBΦ, have been measured using 34 semileptonically and 54 hadronically decaying W+W- candidate events. The events were selected in the data recorded during 1996 with the ALEPH detector at 172 GeV, corresponding to an integrated luminosity of 10.65 pb-1. The triple gauge-boson couplings have been measured using optimal observables constructed from kinematic information of W+W- events. The results are in agreement with the Standard Model expectation.
Measurement of the tt¯ production cross section in pp¯ collisions at s=1.96 TeV in dilepton final states
We present a measurement of the top quark pair ($t\bar{t}$) production cross section ($\sigma_{t\bar{t}}$) in $p\bar{p}$ collisions at $\sqrt{s}=1.96$ TeV using 230 pb$^{-1}$ of data collected by the D0 experiment at the Fermilab Tevatron Collider. We select events with one charged lepton (electron or muon), missing transverse energy, and jets in the final state. We employ lifetime-based b-jet identification techniques to further enhance the $t\bar{t}$ purity of the selected sample. For a top quark mass of 175 GeV, we measure $\sigma_{t\bar{t}}=8.6^{+1.6}_{-1.5}(stat.+syst.)\pm 0.6(lumi.)$ pb, in agreement with the standard model expectation
Fermi-Dirac correlations in Lambda pairs in hadronic Z decays
Two-particle correlations of Lambda Lambda and pairs have been studied in multihadronic Z decays recorded with the ALEPH detector at LEP in the years from 1992 to 1995. The correlations were measured as a function of the four-momentum difference Q of the pair. A depletion of events is observed in the region Q 2 GeV the fraction of pairs with spin one is consistent with the value of 0.75 expected for a statistical spin mixture, whilst for Q pairs, where no Fermi-Dirac correlations are expected, the spin one fraction is measured to be consistent with 0.75 over the entire analysed Q range. (C) 2000 Elsevier Science B.V. All rights reserved.
Tau hadronic branching ratios
From 64492 selected tau-pair events, produced at the Zeta(o) resonance, the measurement of the tau decays into hadrons from a global analysis using 1991, 1992 and 1993 ALEPH data is presented. Special emphasis is given to the reconstruction of photons and pi(o)'s, and the removal of fake photons. A detailed study of the systematics entering the pi(o) reconstruction is also given. A complete and consistent set of tau hadronic branching ratios is presented for 18 exclusive modes. Most measurements are more precise than the present world average. The new level of precision reached allows a stringent test of tau - mu universality in hadronic decays, g(tau)/g(mu) = 1.0013 +/- 0.0095, and the fir…
Measurement of the shape of the boson rapidity distribution forpp¯→Z/γ*→e+e−+Xevents produced atsof 1.96 TeV
We present a measurement of the shape of the boson rapidity distribution for p (p) over bar -> Z/gamma(*)-> e(+)e(-)+X events at a center-of-mass energy of 1.96 TeV. The measurement is made for events with electron-positron mass 71 < M-ee < 111 GeV and uses 0.4 fb(-1) of data collected at the Fermilab Tevatron collider with the D0 detector. This measurement significantly reduces the uncertainties on the rapidity distribution in the forward region compared with previous measurements. Predictions of next-to-next-to-leading order (NNLO) QCD are found to agree well with the data over the full rapidity range.
Measurement of the lifetime difference in the B$_s^0$ system
We present a study of the decay B_s^0 -> J/psi phi We obtain the CP-odd fraction in the final state at time zero, R_perp = 0.16 +/- 0.10 (stat) +/- 0.02 (syst), the average lifetime of the (B_s, B_sbar) system, tau (B_s^0) =1.39^{+0.13}_{-0.16} (stat) ^{+0.01}_{-0.02} (syst) ps, and the relative width difference between the heavy and light mass eigenstates, Delta Gamma/Gamma = (Gamma_L - Gamma_H)/Gamma =0.24^{+0.28}_{-0.38} (stat) ^{+0.03}_{-0.04} (syst). With the additional constraint from the world average of the B_s^0$lifetime measurements using semileptonic decays, we find tau (B_s^0)= 1.39 +/- 0.06 ~ps and Delta Gamma/\Gamma = 0.25^{+0.14}_{-0.15}. For the ratio of the B_s^0 and B^0 li…
Measurement of the Forward-Backward Charge Asymmetry and Extraction ofsin2θWeffinpp¯→Z/γ*+X→e+e−+XEvents Produced ats=1.96 TeV
We present a measurement of the forward-backward charge asymmetry ($A_{FB}$) in $p\bar{p} \to Z/\gamma^{*}+X \to e^+e^-+X$ events at a center-of-mass energy of 1.96 TeV using 1.1 fb$^{-1}$ of data collected with the D0 detector at the Fermilab Tevatron collider. $A_{FB}$ is measured as a function of the invariant mass of the electron-positron pair, and found to be consistent with the standard model prediction. We use the $A_{FB}$ measurement to extract the effective weak mixing angle $sin^2Theta^{eff}_W = 0.2327 \pm 0.0018 (stat.) \pm 0.0006 (syst.)$.
First Study of the Radiation-Amplitude Zero inWγProduction and Limits on AnomalousWWγCouplings ats=1.96 TeV
We present results from a study of p (p) over bar -> W gamma+X events utilizing data corresponding to 0.7 fb(-1) of integrated luminosity at root s = 1.96 TeV collected by the D0 detector at the Fermilab Tevatron Collider. We set limits on anomalous WW gamma couplings at the 95% C.L. The one-dimensional 95% C.L. limits are 0.49 <kappa(gamma)< 1.51 and -0.12 <lambda(gamma)< 0.13. We make the first study of the charge-signed rapidity difference between the lepton and the photon and find it to be indicative of the standard model radiation-amplitude zero in the W gamma system.
Search for heavy particles decaying into a top-quark pair in the fully hadronic final state in pp collisions at s=13 TeV with the ATLAS detector
A search for new particles decaying into a pair of top quarks is performed using proton-proton collision data recorded with the ATLAS detector at the Large Hadron Collider at a center-of-mass energ ...
Search for heavy charged long-lived particles in proton–proton collisions at s=13TeV using an ionisation measurement with the ATLAS detector
This Letter presents a search for heavy charged long-lived particles produced in proton-proton collisions at root s= 13 TeV at the LHC using a data sample corresponding to an integrated luminosity ...
Study of DirectCPViolation inB±→J/ψK±(π±)Decays
We present a search for direct CP violation in $B^{\pm} \to J/\psi K^{\pm}(\pi^{\pm})$ decays. The event sample is selected from 2.8 fb$^{-1}$ of $p\bar{p}$ collisions recorded by D0 experiment in Run II of the Fermilab Tevatron Collider. The charge asymmetry $A_{CP}(B^+ \to J/\psi K^+) = +0.0075 \pm 0.0061$(stat.)$\pm 0.0027$(syst.) is obtained using a sample of approximately 40 thousand $B^{\pm} \to J/\psi K^{\pm}$ decays. The achieved precision is of the same level as the expected deviation predicted by some extensions of the standard model. We also measured the charge asymmetry $A_{CP}(B^+ \to J/\psi \pi^+) = -0.09 \pm 0.08$(stat.)$\pm 0.03$(syst.).
Measurement of the tt¯Z and tt¯W cross sections in proton-proton collisions at s=13 TeV with the ATLAS detector
A measurement of the associated production of a top-quark pair (tt) with a vector boson (W, Z) in proton-proton collisions at a center-of-mass energy of 13 TeV is presented, using 36.1 fb-1 of integrated luminosity collected by the ATLAS detector at the Large Hadron Collider. Events are selected in channels with two same- or opposite-sign leptons (electrons or muons), three leptons or four leptons, and each channel is further divided into multiple regions to maximize the sensitivity of the measurement. The ttZ and ttW production cross sections are simultaneously measured using a combined fit to all regions. The best-fit values of the production cross sections are σttZ=0.95±0.08stat±0.10syst…
Search for γγ decays of a Higgs boson in e+e- collisions at √s up to 209 GeV
A search for events with a photon pair arising from the decay of a Higgs boson produced in association with a fermion pair, is performed in 893 pb-1 of data recorded by the ALEPH detector at LEP at centre-of-mass energies up to 209 GeV. No excess of such events is found over the expected background, An upper limit is derived on the product of the e+e- → HZ cross section and the H → γγ branching fraction as a function of the Higgs boson mass. A fermiophobic Higgs boson produced with the Standard Model cross section is excluded at 95% confidence level for all masses below 105.4 GeV/c2. © 2002 Elsevier Science B.V. All rights reserved.
Simultaneous measurements of thett¯,W+W−, andZ/γ*→ττproduction cross-sections inppcollisions ats=7 TeVwith the ATLAS detector
Simultaneous measurements of the t (t) over bar, W+W-, and Z/gamma* -> tau tau production cross-sections using an integrated luminosity of 4.6 fb(-1) of pp collisions at root s = 7 TeV collected ...
ATLAS data quality operations and performance for 2015-2018 data-taking
The ATLAS detector at the Large Hadron Collider reads out particle collision data from over 100 million electronic channels at a rate of approximately 100 kHz, with a recording rate for physics events of approximately 1 kHz. Before being certified for physics analysis at computer centres worldwide, the data must be scrutinised to ensure they are clean from any hardware or software related issues that may compromise their integrity. Prompt identification of these issues permits fast action to investigate, correct and potentially prevent future such problems that could render the data unusable. This is achieved through the monitoring of detector-level quantities and reconstructed collision ev…
Measurement of the muon charge asymmetry from W boson decays
We present a measurement of the muon charge asymmetry from W boson decays using 0.3 fb^{-1} of data collected at \sqrt{s}=1.96 GeV between 2002 and 2004 with the D0 detector at the Fermilab Tevatron ppbar Collider. We compare our findings with expectations from next-to-leading-order calculations performed using the CTEQ6.1M and MRST04 NLO parton distribution functions. Our findings can be used to constrain future parton distribution function fits.
Search for lepton-flavor-violating decays of the Z boson into a τ lepton and a light lepton with the ATLAS detector
Direct searches for lepton flavor violation in decays of the Z boson with the ATLAS detector at the LHC are presented. Decays of the Z boson into an electron or muon and a hadronically decaying r l ...
Search for heavy long-lived multicharged particles in proton-proton collisions at s=13 TeV using the ATLAS detector
A search for heavy long-lived multicharged particles is performed using the ATLAS detector at the LHC. Data with an integrated luminosity of 36.1 fb(-1) collected in 2015 and 2016 from proton-proto ...
Observation of Higgs boson production in association with a top quark pair at the LHC with the ATLAS detector
Physics letters / B 784, 173 - 191 (2018). doi:10.1016/j.physletb.2018.07.035
Measurement ofD s + meson production inZ decays and of theB s 0 lifetime
D + mesons produced inZ 0→bb events were separated from theZ 0→cc component using a lifetime tag. Using a sample of 1.5 million hadronicZ decays collected with theAleph detector theB 0 andD s + yields have been measured: $$\begin{gathered} \hfill B(b \to \bar B_s^0 )B(\bar B_s^0 \to D_s^ + ) = 0.088 \pm 0.020(stat.) \\ \hfill \pm 0.020(stat.) \\ \hfill B(c \to D_s^ + ) = 0.088 \pm 0.020(stat.)_{ - 0.016}^{ + 0.019} (syst.) \\ \end{gathered} $$ TheB 0 lifetime was measured in aB 0 enriched sample reconstructing the decay length from the vertex of theD + with a hadron from theB 0 decay. The result obtained is: $$\tau _{B_s } = 1.61_{ - 0.29}^{ + 0.30} (stat.)_{ - 0.016}^{ + 0.018} (syst.)$$ p…
Search for a heavy resonance decaying into aZ+jetfinal state inpp¯collisions ats=1.96 TeVusing the D0 detector
We have searched for a heavy resonance decaying into a Z+jet final state in p (p) over bar collisions at a center of mass energy of 1.96 TeV at the Fermilab Tevatron collider using the D0 detector. No indication for such a resonance was found in a data sample corresponding to an integrated luminosity of 370 pb(-1). We set upper limits on the cross section times branching fraction for heavy resonance production at the 95% C.L. as a function of the resonance mass and width. The limits are interpreted within the framework of a specific model of excited quark production.
Measurements of the charge asymmetry in top-quark pair production in the dilepton final state ats=8 TeVwith the ATLAS detector
Measurements of the top--antitop quark pair production charge asymmetry in the dilepton channel are presented using data corresponding to an integrated luminosity of 20.3 fb−1 from pp collisions at a center-of-mass energy of s√=8 TeV collected with the ATLAS detector at the Large Hadron Collider at CERN. Inclusive and differential measurements as a function of the invariant mass, transverse momentum, and longitudinal boost of the tt¯ system are performed both in the full phase space and in a fiducial phase space closely matching the detector acceptance. Two observables are studied: AllC based on the selected leptons and Att¯C based on the reconstructed tt¯ final state. The inclusive asymmet…
Searches for the neutral Higgs bosons of the MSSM in e+e− collisions at centre-of-mass energies of 181–184 GeV
The data collected by ALEPH at LEP at centre-of-mass energies ranging from 181 to 184 GeV, corresponding to an integrated luminosity of 57 pb(-1), are analysed to search for pair-produced neutral Higgs bosons h and A, in the b (b) over bar b (b) over bar and tau(+)tau(-)b (b) over bar final states. Two events are found in the data with 2.5 expected from standard model processes. When combined with the lower energy data collected by ALEPH and with earlier reported searches for associated hZ production, these analyses are interpreted in the context of the minimal supersymmetric extension of the standard model (MSSM). For standard choices of MSSM parameter sets, this combination results in 95%…
Measurement of $B_d$ mixing using opposite-side flavor tagging
We report on a measurement of the $B^0_d$ mixing frequency and the calibration of an opposite-side flavor tagger in the D{\O}experiment. Various properties associated with the $b$ quark on the opposite side of the reconstructed $B$ meson were combined using a likelihood-ratio method into a single variable with enhanced tagging power. Its performance was tested with data, using a large sample of reconstructed semileptonic $B \to \mu \dzero X$ and $B \to \mu \dst X$ decays, corresponding to an integrated luminosity of approximately 1 fb$^{-1}$. The events were divided into groups depending on the value of the combined tagging variable, and an independent analysis was performed in each group. …
Search for resonant second generation slepton production at the Fermilab Tevatron
Made available in DSpace on 2022-04-28T20:09:02Z (GMT). No. of bitstreams: 0 Previous issue date: 2006-01-01 We present a search for supersymmetry in the R-parity violating resonant production and decay of smuons and muon sneutrinos in the channels, 2,3,40. We analyzed 0.38fb-1 of integrated luminosity collected between April 2002 and August 2004 with the D0 detector at the Fermilab Tevatron Collider. The observed number of events is in agreement with the standard model expectation, and we calculate 95% C.L. limits on the slepton production cross section times branching fraction to gaugino plus muon, as a function of slepton and gaugino masses. In the framework of minimal supergravity, we s…
Measurement of Inclusive Differential Cross Sections forΥ(1S)Production inpp¯Collisions ats=1.96 TeV
We present measurements of the inclusive production cross sections of the Upsilon(1S) bottomonium state in p (p) over bar collisions at root s=1.96 TeV. Using the Upsilon(1S)->mu(+)mu(-) decay mode for a data sample of 159 +/- 10 pb(-1) collected by the D0 detector at the Fermilab Tevatron collider, we determine the differential cross sections as a function of the Upsilon(1S) transverse momentum for three ranges of the Upsilon(1S) rapidity: 0 <\y(Upsilon)\<= 0.6, 0.6 <\y(Upsilon)\<= 1.2, and 1.2 <\y(Upsilon)\<= 1.8.
Search for Resonant Pair Production of Neutral Long-Lived Particles Decaying tobb¯inpp¯Collisions ats=1.96 TeV
We report on a first search for resonant pair production of neutral long-lived particles (NLLP) which each decay to a b (b) over bar pair, using 3.6 fb(-1) of data recorded with the D0 detector at the Fermilab Tevatron collider. We search for pairs of displaced vertices in the tracking detector at radii in the range 1.6-20 cm from the beam axis. No significant excess is observed above background, and upper limits are set on the production rate in a hidden-valley benchmark model for a range of Higgs boson masses and NLLP masses and lifetimes.
Search for W ' bosons decaying to an electron and a neutrino with the D0 detector
This Letter describes the search for a new heavy charged gauge boson W' decaying into an electron and a neutrino. The data were collected with the D0 detector at the Fermilab Tevatron proton-antiproton Collider at a center-of-mass energy of 1.96 TeV, and correspond to an integrated luminosity of about 1 inverse femtobarn. Lacking any significant excess in the data in comparison with known processes, an upper limit is set on the production cross section times branching fraction, and a W' boson with mass below 1.00 TeV can be excluded at the 95% C.L., assuming standard-model-like couplings to fermions. This result significantly improves upon previous limits, and is the most stringent to date.
Measurement of the
A new method is presented for the measurement of the mean $\tau$ lepton lifetime using events in which $\tau$'s are pair-produced and both $\tau$'s decay to hadrons and $\nu_\tau$. Based on the correlation between the two $\tau$'s produced at a symmetric $e^+ e^-$ collider, the 3DIP method relies on the three-dimensional information from a double-sided vertex detector and on kinematic constraints for the precise measurement of the $\tau$ decay angles. Using the data collected from 1992 to 1994 with the ALEPH detector at LEP, a $\tau$ lifetime of $288.0 \pm 3.1 \pm 1.3 $\fs is obtained from the sample in which both $\tau$'s decay to one charged track, and $292.8 \pm 5.6 \pm 3.0 $\fs from the…
Search for a heavy Higgs boson decaying into a Z boson and another heavy Higgs boson in the ℓℓbb final state in pp collisions at s=13 TeV with the ATLAS detector
A search for a heavy neutral Higgs boson, A, decaying into a Z boson and another heavy Higgs boson, H, is performed using a data sample corresponding to an integrated luminosity of 36.1 fb(-1) from ...
Search for large extra dimensions via single photon plus missing energy final states at s=1.96TeV
Made available in DSpace on 2022-04-28T20:42:17Z (GMT). No. of bitstreams: 0 Previous issue date: 2008-06-30 We report on a search for large extra dimensions in a data sample of approximately 1fb-1 of pp̄ collisions at s=1.96TeV. We investigate Kaluza-Klein graviton production with a photon and missing transverse energy in the final state. At the 95% C.L. we set limits on the fundamental mass scale MD from 884to 778GeV for two to eight extra dimensions. © 2008 The American Physical Society. Universidad de Buenos Aires, Buenos Aires LAFEX Centro Brasileiro de Pesquisas Físicas, Rio de Janeiro Universidade Do Estado Do Rio de Janeiro, Rio de Janeiro Universidade Federal Do ABC, Santo André In…
Measurement of the Polarization of theΥ(1S)andΥ(2S)States inpp¯Collisions ats=1.96 TeV
We present a study of the polarization of the $\Upsilon(1S)$ and $\Upsilon(2S)$ states using a $1.3 $ fb$^{-1}$ data sample collected by the D0 experiment in 2002--2006 during Run II of the Fermilab Tevatron Collider. We measure the polarization parameter $\alpha=(\sigma_{T}-2\sigma_{L})/(\sigma_{T}+2\sigma_{L})$, where $\sigma_{T}$ and $\sigma_{L}$ are the transversely and longitudinally polarized components of the production cross section, as a function of the transverse momentum ($p_{T}^{\Upsilon}$) for the $\Upsilon(1S)$ and $\Upsilon(2S)$. Significant $p_{T}^{\Upsilon}$-dependent longitudinal polarization is observed for the $\Upsilon(1S)$. A comparison with theoretical models is prese…
Search for heavy charged long-lived particles in the ATLAS detector in 36.1 fb−1 of proton-proton collision data at s=13 TeV
A search for heavy charged long-lived particles is performed using a data sample of 36.1 fb−1 of proton-proton collisions at s=13 TeV collected by the ATLAS experiment at the Large Hadron Collider. The search is based on observables related to ionization energy loss and time of flight, which are sensitive to the velocity of heavy charged particles traveling significantly slower than the speed of light. Multiple search strategies for a wide range of lifetimes, corresponding to path lengths of a few meters, are defined as model independently as possible, by referencing several representative physics cases that yield long-lived particles within supersymmetric models, such as gluinos/squarks …
Search for Higgs boson decays into pairs of light (pseudo)scalar particles in the γγjj final state in pp collisions at s=13TeV with the ATLAS detector
This Letter presents a search for exotic decays of the Higgs boson to a pair of new (pseudo)scalar particles, H→aa , where the a particle has a mass in the range 20–60 GeV, and where one of the a bosons decays into a pair of photons and the other to a pair of gluons. The search is performed in event samples enhanced in vector-boson fusion Higgs boson production by requiring two jets with large invariant mass in addition to the Higgs boson candidate decay products. The analysis is based on the full dataset of pp collisions at s=13TeV recorded in 2015 and 2016 with the ATLAS detector at the CERN Large Hadron Collider, corresponding to an integrated luminosity of 36.7 fb −1 . The data are in a…
Search for new phenomena in final states with an energetic jet and large missing transverse momentum inppcollisions ats=13 TeVusing the ATLAS detector
Results of a search for new phenomena in final states with an energetic jet and large missing transverse momentum are reported. The search uses proton-proton collision data corresponding to an inte ...
Search for Large Extra Spatial Dimensions in the Dielectron and Diphoton Channels inpp¯Collisions ats=1.96 TeV
We report on a search for large extra spatial dimensions in the dielectron and diphoton channels using a data sample of 1.05 \invfb of \ppb collisions at a center-of-mass energy of 1.96 TeV collected by the D0 detector at the Fermilab Tevatron Collider. The invariant mass spectrum of the data agrees well with the prediction of the standard model. We find 95% C.L. lower limits on the effective Planck scale between 2.1 and 1.3 TeV for 2 to 7 extra dimensions.
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.
Measurement of theCP-violation parameter ofB0mixing and decay withpp¯→μμXdata
We measure the dimuon charge asymmetry A in p (p) over bar collisions at a center of mass energy root s=1960 GeV. The data was recorded with the D0 detector and corresponds to an integrated luminosity of approximately 1.0 fb(-1). Assuming that the asymmetry A is due to asymmetric B-0 (B) over bar (0) mixing and decay, we extract the CP-violation parameter of B-0 mixing and decay: ((epsilon B0))/(1+vertical bar epsilon B0 vertical bar 2)=(AB0)/(4)= -0.0023 +/- 0.0011(stat)+/- 0.0008(syst).A(B)(0) is the dimuon charge asymmetry from decays of B-0(B) over bar (0) pairs. The general case, with CP violation in both B-0 and B-s(0) systems, is also considered. Finally we obtain the forward-backwar…
Search for lepton-flavor violation in different-flavor, high-mass final states in pp collisions at s=13 TeV with the ATLAS detector
A search is performed for a heavy particle decaying into different-flavor, dilepton pairs (e mu, e tau or mu tau), using 36.1 fb(-1) of proton-proton collision data at root s = 13 TeV collected in ...
Measurement of the W mass by direct reconstruction in e+e- collisions at 172 GeV
The mass of the W boson is obtained from reconstructed invariant mass distributions in W-pair events. The sample of W pairs is selected from 10.65 pb(-1) collected with the ALEPH detector at a mean centre-of-mass energy of 172.09 GeV. The invariant mass distribution of simulated events are fitted to the experimental; distributions and the following W masses are obtained: WW --> , m(W) = 81.30 +/- 0.47(stat.) +/- 0.11(syst.)GeV/c(2), WW --> l nu (l=e,mu), m(W) = 80.54 +/- 0.47(stat.) +/- 0.11(syst.)GeV/c(2), WW --> tau nu, m(W) = 79.56 +/- 1.08(stat.) +/- 0.23(syst.) GeV/c(2). The statistical errors are the expected errors for Monte Carlo samples of the same integrated luminosity as the data…
Measurement of the W boson helicity in top quark decay at D0
We present a measurement of the fraction f_+ of right-handed W bosons produced in top quark decays, based on a candidate sample of ttbar events in the l+jets and dilepton decay channels corresponding to an integrated luminosity of 370 pb^-1 collected by the DO detector at the Fermilab Tevatron ppbar Collider at sqrt{s}=1.96 TeV. We reconstruct the decay angle theta^* for each lepton. By comparing the \cos\theta^* distribution from the data with those for the expected background and signal for various values of f_+, we find $f_+=0.056 +- 0.080 (stat) +- 0.057 (syst)}. (f_+ < 0.23 at 95% C.L.), consistent with the standard model prediction of f_+=3.6 x10^-4.
Measurement ofBs0Mixing Parameters from the Flavor-Tagged DecayBs0→J/ψϕ
From an analysis of the flavor-tagged decay B-s(0)-> J/psi phi we obtain the width difference between the B-s(0) light and heavy mass eigenstates, Delta Gamma(s)=0.19 +/- 0.07(stat)(-0.01)(+0.02)(syst) ps(-1), and the CP-violating phase, phi(s)=-0.57(-0.30)(+0.24)(stat)(-0.02)(+0.08)(syst). The allowed 90% CL intervals of Delta Gamma(s) and phi(s) are 0.06 <Delta Gamma(s)< 0.30 ps(-1) and -1.20 <phi(s)< 0.06, respectively. The data sample corresponds to an integrated luminosity of 2.8 fb(-1) accumulated with the D0 detector at the Fermilab Tevatron collider.
Search for TeV-scale gravity signatures in final states with leptons and jets with the ATLAS detector at s=7 TeV
A search for physics beyond the Standard Model, in final states with at least one high transverse momentum charged lepton (electron or muon) and two additional high transverse momentum leptons or jets, is performed using 3.2 fb−1 of proton–proton collision data recorded by the ATLAS detector at the Large Hadron Collider in 2015 at √s = 13 TeV. The upper end of the distribution of the scalar sum of the transverse momenta of leptons and jets is sensitive to the production of high-mass objects. No excess of events beyond Standard Model predictions is observed. Exclusion limits are set for models of microscopic black holes with two to six extra dimensions.
Construction, assembly and tests of the ATLAS electromagnetic barrel calorimeter
The construction and assembly of the two half barrels of the ATLAS central electromagnetic calorimeter and their insertion into the barrel cryostat are described. The results of the qualification tests of the calorimeter before installation in the LHC ATLAS pit are given.
Search for single top quark production in pp¯ collisions at s=1.96 TeV
We present a search for electroweak production of single top quarks in the s-channel and t-channel using neural networks for signal-background separation. We have analyzed 230 pb(-1) of data collected with the DO detector at the Fermilab Tevatron Collider at a center-of-mass energy of 1.96 TeV and find no evidence for a single top quark signal. The resulting 95% confidence level upper limits on the single top quark production cross sections are 6.4 pb in the s-channel and 5.0 ph in the t-channel. (c) 2005 Elsevier B.V. All rights reserved.
Measurement of the lifetime of the Bc +- meson in the semileptonic decay channel
Using approximately 1.3 fb-1 of data collected by the D0 detector between 2002 and 2006, we measure the lifetime of the B_c meson in the B_c -> J/psi mu nu X final state. A simultaneous unbinned likelihood fit to the J/\psi+mu invariant mass and lifetime distributions yields a signal of 881 +/- 80 (stat) candidates and a lifetime measurement of \tau(B_c) = 0.448 +0.038 -0.036 (stat) +/- 0.032 (syst) ps.
Search for higgs bosons decaying to tau pairs in pp̄ collisions with the D0 detector
Made available in DSpace on 2022-04-28T20:43:10Z (GMT). No. of bitstreams: 0 Previous issue date: 2008-08-14 Science and Technology Facilities Council We present a search for the production of neutral Higgs bosons decaying into τ+τ- final states in pp̄ collisions at a center-of-mass energy of 1.96 TeV. The data, corresponding to an integrated luminosity of approximately 1fb-1, were collected by the D0 experiment at the Fermilab Tevatron Collider. Limits on the production cross section times branching ratio are set. The results are interpreted in the minimal supersymmetric standard model yielding limits that are the most stringent to date at hadron colliders. © 2008 The American Physical Soc…
Search for AssociatedWand Higgs Boson Production inpp¯Collisions ats=1.96 TeV
We present results of a search for WH -> l nu b (b) over bar production in p (p) over bar collisions based on the analysis of 1.05 fb(-1) of data collected by the D0 experiment at the Fermilab Tevatron, using a neural network for separating the signal from backgrounds. No signal-like excess is observed, and we set 95% C. L. upper limits on the WH production cross section multiplied by the branching ratio for H -> b (b) over bar for Higgs boson masses between 100 and 150 GeV. For a mass of 115 GeV, we obtain an observed (expected) limit of 1.5 (1.4) pb, a factor of 11.4 (10.7) times larger than the standard model prediction.
Performance of the ATLAS Hadronic End-Cap Calorimeter in Beam Tests
Abstract Modules of the ATLAS liquid argon Hadronic End-cap Calorimeter (HEC) were exposed to beams of electrons, muons and pions in the energy range 6⩽ E ⩽200 GeV at the CERN SPS. A description of the HEC and of the beam test setup are given. Results on the energy response and resolution are presented and compared with simulations. The ATLAS energy resolution for jets in the end-cap region is inferred and meets the ATLAS requirements.
Electron and photon energy calibration with the ATLAS detector using 2015-2016 LHC proton-proton collision data
Artículo realizado por muchos autores. Solo se referencian el que aparece en primer lugar, el nombre del grupo de colaboración y los autores que firman como pertenecientes a la UAM
Limits on anomalous trilinear gauge couplings fromWW→e+e−,WW→e±μ∓, andWW→μ+μ−events frompp¯collisions ats=1.96 TeV
Limits are set on anomalous WW gamma and WWZ trilinear gauge couplings using W+W--> e(+)nu(e)e(-)(nu) over bar (e), W+W--> e(+/-)nu(e)mu(-/+)nu(mu), and W+W-->mu(+)nu(mu)mu(-)(nu) over bar (mu) events. The data set was collected by the Run II D0 detector at the Fermilab Tevatron Collider and corresponds to approximately 250 pb(-1) of integrated luminosity at root s=1.96 TeV. Under the assumption that the WW gamma couplings are equal to the WWZ couplings and using a form factor scale of Lambda=2.0 TeV, the combined 95% C.L. one-dimensional coupling limits from all three channels are -0.32 <Delta kappa < 0.45 and -0.29 <lambda < 0.30.
Measurement of Semileptonic Branching Fractions ofBMesons to NarrowD**States
Using the data accumulated in 2002-2004 with the D0 detector in proton-antiproton collisions at the Fermilab Tevatron collider with a center-of-mass energy of 1.96 TeV, the branching fractions of the decays B ->(D) over bar (0)(1)(2420)mu(+)nu(mu)X and B ->(D) over bar (*0)(2)(2460)mu(+)nu(mu)X and their ratio have been measured: B (b) over bar -> B)xB(B -> (D) over bar (0)(1)mu(+)nu(mu)X)xB((D) over bar (0)(1)-> D(*-)pi(+))=[0.087 +/- 0.007(stat)+/- 0.014(syst)]%; B((b) over bar -> B)xB(B ->(D) over bar (*0)(2)mu(+)nu(mu)X)xB((D) over bar (*0)(2)-> D(*-)pi(+))=[0.035 +/- 0.007(stat)+/- 0.008(syst)]% and [B(B ->(D) over bar (*0)(2)mu(+)nu(mu)X)xB((D) over bar (*0)(2)-> D(*-)pi(+))]/[B(B ->(…
Search for charged Higgs bosons through the violation of lepton universality in t(t)over-bar events using pp collision data at root s=7 TeV with the ATLAS experiment
In several extensions of the Standard Model, the top quark can decay into a bottom quark and a light charged Higgs boson H [superscript +], t → bH [superscript +], in addition to the Standard Model decay t → bW. Since W bosons decay to the three lepton generations equally, while H [superscript +] may predominantly decay into τν, charged Higgs bosons can be searched for using the violation of lepton universality in top quark decays. The analysis in this paper is based on 4.6 fb[superscript −1] of proton-proton collision data at √s = 7 TeV collected by the ATLAS experiment at the Large Hadron Collider. Signatures containing leptons (e or μ) and/or a hadronically decaying τ (τ [subscript had])…
Search for Neutral Higgs Bosons Decaying to Tau Pairs inpp¯Collisions ats=1.96 TeV
A search for the production of neutral Higgs bosons {Phi} decaying into {tau}{sup +}{tau}{sup -} final states in p{bar p} collisions at a center-of-mass energy of 1.96 TeV is presented. The data, corresponding to an integrated luminosity of approximately 325 pb{sup -1}, were collected by the D0 experiment at the Fermilab Tevatron Collider. Since no excess compared to the expectation from standard model processes is found, limits on the production cross section times branching ratio are set. The results are combined with those obtained from the D0 search for {Phi}b({bar b}) {yields} b{bar b}b({bar b}) and are interpreted in the minimal supersymmetric standard model.
Two-particle azimuthal correlations in photonuclear ultraperipheral Pb+Pb collisions at 5.02 TeV with ATLAS
We thank CERN for the very successful operation of the LHC, as well as the support staff from our institutions without whom ATLAS could not be operated efficiently. We acknowledge the support of ANPCyT, Argentina, YerPhI, Armenia, ARC, Australia, BMWFW and FWF, Austria, ANAS, Azerbaijan, SSTC, Belarus, CNPq and FAPESP, Brazil, NSERC, NRC, and CFI, Canada, CERN and ANID, Chile, CAS, MOST, and NSFC, China, COLCIENCIAS, Colombia, MSMT CR, MPO CR, and VSC CR, Czech Republic, DNRF and DNSRC, Denmark, IN2P3-CNRS and CEA-DRF/IRFU, France, SRNSFG, Georgia, BMBF, HGF, and MPG, Germany, GSRT, Greece, RGC and Hong Kong SAR, China, ISF and Benoziyo Center, Israel, INFN, Italy, MEXT and JSPS, Japan, CNR…
Search for chargino-neutralino production using recursive jigsaw reconstruction in final states with two or three charged leptons in proton-proton collisions at s=13 TeV with the ATLAS detector
A search for electroweak production of supersymmetric particles is performed in two-lepton and three-lepton final states using recursive jigsaw reconstruction, a technique that assigns reconstructed objects to the most probable hemispheres of the decay trees, allowing one to construct tailored kinematic variables to separate the signal and background. The search uses data collected in 2015 and 2016 by the ATLAS experiment in s=13 TeV proton-proton collisions at the CERN Large Hadron Collider corresponding to an integrated luminosity of 36.1 fb-1. Chargino-neutralino pair production, with decays via W/Z bosons, is studied in final states involving leptons and jets and missing transverse mome…
Observation of Long-Range Elliptic Azimuthal Anisotropies ins=13and 2.76 TeVppCollisions with the ATLAS Detector
ATLAS has measured two-particle correlations as a function of relative azimuthal-angle, $\Delta \phi$, and pseudorapidity, $\Delta \eta$, in $\sqrt{s}$=13 and 2.76 TeV $pp$ collisions at the LHC using charged particles measured in the pseudorapidity interval $|\eta|$<2.5. The correlation functions evaluated in different intervals of measured charged-particle multiplicity show a multiplicity-dependent enhancement at $\Delta \phi \sim 0$ that extends over a wide range of $\Delta\eta$, which has been referred to as the "ridge". Per-trigger-particle yields, $Y(\Delta \phi)$, are measured over 2<$|\Delta\eta|$<5. For both collision energies, the $Y(\Delta \phi)$ distribution in all multiplicity …
Measurement of the Electron Charge Asymmetry inpp¯→W+X→eν+XEvents ats=1.96 TeV
We present a measurement of the electron charge asymmetry in ppbar->W+X->enu+X events at a center of mass energy of 1.96 TeV using 0.75 fb-1 of data collected with the D0 detector at the Fermilab Tevatron Collider. The asymmetry is measured as a function of the electron transverse momentum and pseudorapidity in the interval (-3.2, 3.2) and is compared with expectations from next-to-leading order calculations in perturbative quantum chromodynamics. These measurements will allow more accurate determinations of the proton parton distribution functions.
Measurement of the top quark mass in the lepton+jets channel using the ideogram method
A measurement of the top quark mass using events with one charged lepton, missing transverse energy, and jets in the final state, collected by the D0 detector from p-pbar collisions at sqrt{s} = 1.96 TeV at the Fermilab Tevatron collider, is presented. A constrained fit is used to fully reconstruct the kinematics of the events. For every event a top quark mass likelihood is calculated taking into account all possible jet assignments and the probability that an event is signal or background. Lifetime-based identification of b jets is employed to enhance the separation between t-tbar signal and background from other physics processes and to improve the assignment of the observed jets to the q…
Search for neutral supersymmetric higgs bosons in multijet events at s=1.96TeV
Made available in DSpace on 2022-04-28T20:06:00Z (GMT). No. of bitstreams: 0 Previous issue date: 2005-10-07 We have performed a search for neutral Higgs bosons produced in association with bottom quarks in pp collisions, using 260pb-1 of data collected with the D0 detector in Run II of the Fermilab Tevatron Collider. The cross sections for these processes are enhanced in many extensions of the standard model (SM), such as in its minimal supersymmetric extension at large tanâ□¡Î. The results of our analysis agree with expectations from the SM, and we use our measurements to set upper limits on the production of neutral Higgs bosons in the mass range of 90 to 150 GeV. © 2005 The American Ph…
Measurement of B(t→Wb)/B(t→Wq) at s=1.96TeV
We present the measurement of R = B(t -> Wb)/B(t -> Wq) in pp collisions at root s = 1.96 TeV, using 230 pb(-1) of data collected by the DO experiment at the Fermilab Tevatron Collider. We fit simultaneously R and the number (N-tt) of selected top quark pairs (tt), to the number of identified b-quark jets in events with one electron or one muon, three or more jets, and high transverse energy imbalance. To improve sensitivity, kinematical properties of events with no identified b-quark jets are included in the fit. We measure R = 1.03(-0.17)(0.19) (stat + syst), in good agreement with the standard model. We set lower limits of R > 0.61 and vertical bar V-tb vertical bar > 0.78 at 95% confide…
Search for Randall-Sundrum gravitons in dilepton and diphoton final states
We report the first direct search for the Kaluza-Klein (KK) modes of Randall-Sundrum gravitons using dielectron, dimuon, and diphoton events observed with the D0 detector operating at the Fermilab Tevatron ppbar Collider at sqrt(s) = 1.96 TeV. No evidence for resonant production of gravitons has been found in the data corresponding to an integrated luminosity of approximately 260 pb^-1. Lower limits on the mass of the first KK mode at the 95% C.L. have been set between 250 and 785 GeV, depending on its coupling to SM particles.
Search for associated production of charginos and neutralinos in the trilepton final state using 2.3 fb-1 of data
We report the results of a search for associated production of charginos and neutralinos using a data set corresponding to an integrated luminosity of 2.3 fb-1 collected with the D0 experiment during Run II of the Tevatron proton-antiproton collider. Final states containing three charged leptons and missing transverse energy are probed for a signal from supersymmetry with four dedicated trilepton event selections. No evidence for a signal is observed, and we set limits on the product of production cross section and leptonic branching fraction. Within minimal supergravity, these limits translate into bounds on m_0 and m_1/2 that are well beyond existing limits.
Beam-induced and cosmic-ray backgrounds observed in the ATLAS detector during the LHC 2012 proton-proton running period
This paper discusses various observations on beam-induced and cosmic-ray backgrounds in the ATLAS detector during the LHC 2012 proton-proton run. Building on published results based on 2011 data, the correlations between background and residual pressure of the beam vacuum are revisited. Ghost charge evolution over 2012 and its role for backgrounds are evaluated. New methods to monitor ghost charge with beam-gas rates are presented and observations of LHC abort gap population by ghost charge are discussed in detail. Fake jets from colliding bunches and from ghost charge are analysed with improved methods, showing that ghost charge in individual radio-frequency buckets of the LHC can be resol…
Comparison between simulated and observed LHC beam backgrounds in the ATLAS experiment at E beam =4 TeV
Results of dedicated Monte Carlo simulations of beam-induced background (BIB) in the ATLAS experiment at the Large Hadron Collider (LHC) are presented and compared with data recorded in 2012. During normal physics operation this background arises mainly from scattering of the 4 TeV protons on residual gas in the beam pipe. Methods of reconstructing the BIB signals in the ATLAS detector, developed and implemented in the simulation chain based on the FLUKA Monte Carlo simulation package, are described. The interaction rates are determined from the residual gas pressure distribution in the LHC ring in order to set an absolute scale on the predicted rates of BIB so that they can be compared qua…
Search for Doubly Charged Higgs Boson Pair Production in the Decay toμ+μ+μ−μ−inpp¯Collisions ats=1.96 TeV
A search for pair production of doubly charged Higgs bosons in the process p (p) over bar -->H++H---->mu(+)mu(+)mu(-)mu(-) is performed with the D0 run II detector at the Fermilab Tevatron. The analysis is based on a sample of inclusive dimuon data collected at an energy of roots=1.96 TeV, corresponding to an integrated luminosity of 113 pb(-1). In the absence of a signal, 95% confidence level mass limits of M(H-L(+/-+/-))>118.4 GeV/c(2) and M(H-R(+/-+/-))>98.2 GeV/c(2) are set for left-handed and right-handed doubly charged Higgs bosons, respectively, assuming 100% branching into muon pairs.
ZZ→l+l−νν¯production inpp¯collisions ats=1.96 TeV
We describe a search for Z boson pair production in pp collisions at sqrt(s)= 1.96 TeV with the D0 detector at the Fermilab Tevatron Collider using a data sample corresponding to an integrated luminosity of 2.7 fb^-1. Using the final state decay ZZ to llvv (where l = e or mu) we measure a signal with a 2.6 standard deviations significance (2.0 expected) and measure a cross section of sigma(pp to ZZ + X) = 2.01 +- 0.93 (stat.) +- 0.29 (sys.) pb.
Search for charginos nearly mass degenerate with the lightest neutralino in e+e− collisions at centre-of-mass energies up to 209 GeV
A search for charginos nearly mass degenerate with the lightest neutralino is performed with the data collected by the ALEPH detector at LEP, at centre-of-mass energies between 189 and 209 GeV, corresponding to an integrated luminosity of 628 pb-1. The analysis is based on the detection of isolated and energetic initial state radiation photons, produced in association with chargino pairs whose decay products have little visible energy. The number of candidate events observed is in agreement with that expected from Standard Model background sources. These results are combined with those of other direct searches for charginos, and a lower limit of 88 GeV/c2 at 95 % confidence level is derived…
Measurement of the e+e- → ZZ production cross section at centre-of-mass energies of 183 and 189 GeV
The ee -> ZZ cross section at sqrt(s)=182.7 and 188.6 GeV has been measured using the ALEPH detector. The analysis covers all of the visible ZZ final states and yields cross section measurements of sigma_ZZ(182.7 GeV) = 0.11 +- (0.16,0.11) (stat.) +- 0.04 (syst.) pb and sigma_ZZ(188.6 GeV) = 0.67 +- 0.13 (stat.) +- 0.04 (syst.) pb consistent with the Standard Model expectations.
Exclusive production of pion and kaon meson pairs in two photon collisions at LEP
Exclusive production of pi and K meson pairs in two photon collisions is measured with ALEPH data collected between 1992 and 2000. Cross-sections are presented as a function of cos theta* and invariant mass, for \ cos theta* \ < 0.6 and invariant masses between 2.0 and 6.0 GeV/c(2) (2.25 and 4.0 GeV/c(2)) for pions (kaons). The shape of the distributions are found to be well described by QCD predictions but the data have a significantly higher normalization. (C) 2003 Published by Elsevier B.V.
Measurement of Dijet Angular Distributions ats=1.96 TeVand Searches for Quark Compositeness and Extra Spatial Dimensions
We present the first measurement of dijet angular distributions in ppbar collisions at sqrt{s}=1.96TeV at the Fermilab Tevatron Collider. The measurement is based on a dataset corresponding to an integrated luminosity of up to 0.7fb-1 collected with the D0 detector. Dijet angular distributions have been measured over a range of dijet masses, from 0.25TeV to above 1.1TeV. The data are in good agreement with the predictions of perturbative QCD and are used to constrain new physics models including quark compositeness, large extra dimensions, and TeV-1 scale extra dimensions. For all models we set the most stringent direct limits to date.
Observation of Single Top Quark Production
We report observation of the electroweak production of single top quarks in ppbar collisions at sqrt(s) = 1.96 TeV based on 2.3 fb^-1 of data collected by the D0 detector at the Fermilab Tevatron Collider. Using events containing an isolated electron or muon and missing transverse energy, together with jets originating from the fragmentation of b quarks, we measure a cross section of sigma(ppbar -> tb + X, tqb + X) = 3.94 +- 0.88 pb. The probability to measure a cross section at this value or higher in the absence of signal is 2.5 x 10^-7, corresponding to a 5.0 standard deviation significance for the observation.
Search for the Decay of the Higgs Boson to Charm Quarks with the ATLAS Experiment
A direct search for the standard model Higgs boson decaying to a pair of charm quarks is presented. Associated production of the Higgs and Z bosons, in the decay mode ZH→ℓ+ℓ−c¯c is studied. A data set with an integrated luminosity of 36.1 fb−1 of pp collisions at √s=13TeV recorded by the ATLAS experiment at the LHC is used. The H→c¯c signature is identified using charm-tagging algorithms. The observed (expected) upper limit on σ(pp→ZH)×B(H→c¯c) is 2.7 (3.9+2.1−1.1) pb at the 95% confidence level for a Higgs boson mass of 125 GeV, while the standard model value is 26 fb.
Observation of theBcMeson in the Exclusive DecayBc→J/ψπ
A fully reconstructed B-c -> J/psi pi signal is observed with the D0 detector at the Fermilab Tevatron p (p) over bar collider using 1.3 fb(-1) of integrated luminosity. The signal consists of 54 +/- 12 candidates with a significance that exceeds 5 standard deviations, and confirms earlier observations of this decay. The measured mass of the B-c meson is 6300 +/- 14(stat)+/- 5(syst) MeV/c(2).
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 four-top-quark production in the single-lepton and opposite-sign dilepton final states in pp collisions at s=13 TeV with the ATLAS detector
A search for four-top-quark production, tttt, is presented. It is based on proton-proton collision data with a center-of-mass energy s=13 TeV collected by the ATLAS detector at the Large Hadron Collider during the years 2015 and 2016, corresponding to an integrated luminosity of 36.1 fb-1. Data are analyzed in both the single-lepton and opposite-sign dilepton channels, characterized by the presence of one or two isolated electrons or muons with high-transverse momentum and multiple jets. A data-driven method is used to estimate the dominant background from top-quark pair production in association with jets. No significant excess above the Standard Model expectation is observed. The result i…
First measurement of the forward-backward charge asymmetry in top quark pair production
We present the first measurement of the integrated forward-backward charge asymmetry in top-antitop quark pair (ttbar) production in proton-antiproton collisions in the lepton plus jets final state. Using a b-jet tagging algorithm and kinematic reconstruction assuming ttbar+X production and decay, a sample of 0.9fb-1 of data, collected by the D0 experiment at the Fermilab Tevatron Collider, is used to measure the asymmetry for different jet multiplicities. The result is also used to set upper limits on ttbar+X production via a Z' resonance.
Observation of top-quark pair production in association with a photon and measurement of thett¯γproduction cross section inppcollisions ats=7TeV using the ATLAS detector
A search is performed for top-quark pairs (t (t) over bar) produced together with a photon (gamma) with transverse energy greater than 20 GeV using a sample of t (t) over bar candidate events in final states with jets, missing transverse momentum, and one isolated electron or muon. The data set used corresponds to an integrated luminosity of 4.59 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. In total, 140 and 222 t (t) over bar gamma candidate events are observed in the electron and muon channels, to be compared to the expectation of 79 +/- 26 and 120 +/- 39 non-t (t) over bar gamma background events,…
Inclusive semileptonic branching ratios of b hadrons produced in Z decays
A measurement of the inclusive semileptonic branching ratios of b hadrons produced in Z decay is presented, using four million hadronic events collected by the ALEPH detector from 1991 to 1995. Electrons and muons are selected opposite to b-tagged hemispheres. Two different methods are explored to distinguish the contributions from direct $\bl$ and cascade $\bcl$ decays to the total lepton yield. One is based on the lepton transverse momentum spectrum, the other makes use of the correlation between the charge of the lepton and charge estimators built from tracks in the opposite hemisphere of the event. The latter method reduces the dependence on the modelling of semileptonic b decays. The r…
Observation of an Excited $B^{\pm}_c$ Meson State with the ATLAS Detector
A search for excited states of the B±c meson is performed using 4.9 fb-1 of 7 TeV and 19.2 fb-1 of 8 TeV pp collision data collected by the ATLAS experiment at the LHC. A new state is observed through its hadronic transition to the ground state, with the latter detected in the decay B±c→J/ψπ±. The state appears in the m(Bc±π+π-)-m(Bc±)-2m(π±) mass difference distribution with a significance of 5.2 standard deviations. The mass of the observed state is 6842±4±5 MeV, where the first error is statistical and the second is systematic. The mass and decay of this state are consistent with expectations for the second S-wave state of the B±c meson, B±c(2S).
Femtoscopy with identified charged pions in proton-lead collisions at sNN=5.02 TeV with ATLAS
Bose-Einstein correlations between identified charged pions are measured for $p$+Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV using data recorded by the ATLAS detector at the LHC corresponding to a total integrated luminosity of $28$ $\mathrm{nb}^{-1}$. Pions are identified using ionization energy loss measured in the pixel detector. Two-particle correlation functions and the extracted source radii are presented as a function of collision centrality as well as the average transverse momentum ($k_{\mathrm{T}}$) and rapidity ($y^{\star}_{\pi\pi}$) of the pair. Pairs are selected with a rapidity $-2 < y^{\star}_{\pi\pi} < 1$ and with an average transverse momentum $0.1 < k_{\mathrm{T}} <…
Observation of an excess in the search for the Standard Model Higgs boson at ALEPH
A search has been performed for the Standard Model Higgs boson in the data sample collected with the ALEPH detector at LEP, at centre-of-mass energies up to 209GeV. An excess of 3sigma beyond the background expectation is found, consistent with the production of the Higgs boson with a mass near 114GeV/c2. Much of this excess is seen in the four-jet analyses, where three high purity events are selected.
Measurement of the Inclusive Jet Cross Section inpp¯Collisions ats=1.96 TeV
We report on a measurement of the inclusive jet cross section in p (p) over bar collisions at a center-of-mass energy root s = 1.96 TeV using data collected by the D0 experiment at the Fermilab Tevatron Collider corresponding to an integrated luminosity of 0: 70 fb(-1). The data cover jet transverse momenta from 50 to 600 GeV and jet rapidities in the range -2.4 to 2.4. Detailed studies of correlations between systematic uncertainties in transverse momentum and rapidity are presented, and the cross section measurements are found to be in good agreement with next-to-leading order QCD calculations.
Measurements of Higgs boson properties in the diphoton decay channel with 36 fb−1 of pp collision data at s=13 TeV with the ATLAS detector
Properties of the Higgs boson are measured in the two-photon final state using 36.1 fb-1 of proton? proton collision data recorded at ffiffi √s = 13 TeV by the ATLAS experiment at the Large Hadron Collider. Cross-section measurements for the production of a Higgs boson through gluon-gluon fusion, vectorboson fusion, and in association with a vector boson or a top-quark pair are reported. The signal strength, defined as the ratio of the observed to the expected signal yield, is measured for each of these production processes as well as inclusively. The global signal strength measurement of 0.99 ± 0.14 improves on the precision of the ATLAS measurement at √s = 7 and 8 TeV by a factor of two. …
Evidence for production of single top quarks and first direct measurement of |Vtb|.
The D0 Collaboration presents first evidence for the production of single top quarks at the Fermilab Tevatron ppbar collider. Using a 0.9 fb^-1 dataset, we apply a multivariate analysis to separate signal from background and measure sigma(ppbar->tb+X,tqb+X) = 4.9 +- 1.4 pb. The probability to measure a cross section at this value or higher in the absence of signal is 0.035%, corresponding to a 3.4 standard deviation significance. We use the cross section measurement to directly determine the CKM matrix element that describes the Wtb coupling and find 0.68 < |Vtb| <= 1 at 95% C.L. within the standard model.