403 research outputs found
Measurement of the prompt J/ψ pair production cross-section in pp collisions at √s=8 TeV with the ATLAS detector
No full textThe production of two prompt J/ψ mesons, each with transverse momenta pT>8.5 GeV and rapidity |y|<2.1, is studied using a sample of proton-proton collisions at √s=8 TeV, corresponding to an integrated luminosity of 11.4 fb −1 collected in 2012 with the ATLAS detector at the LHC. The differential cross-section, assuming unpolarised J/ψ production, is measured as a function of the transverse momentum of the lower- pT J/ψ meson, di- J/ψ pT and mass, the difference in rapidity between the two J/ψ mesons, and the azimuthal angle between the two J/ψ mesons. The fraction of prompt pair events due to double parton scattering is determined by studying kinematic correlations between the two J/ψ mesons. The total and double parton scattering cross-sections are compared with predictions. The effective cross-section of double parton scattering is measured to be σeff=6.3±1.6(stat)±1.0(syst) mb
Measurements of and production in collisions at TeV with the ATLAS detector
No full textSee paper for full list of authors - 42 pages in total, author list starting page 26, 10 figures, 8 tables. Submitted to JHEP. All figures including auxiliary figures are available at http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/BPHY-2015-03/International audienceDifferential cross sections are presented for the prompt and non-prompt production of the hidden-charm states and , in the decay mode , measured using 11.4 fb of collisions at TeV by the ATLAS detector at the LHC. The ratio of cross-sections is also given, separately for prompt and non-prompt components, as well as the non-prompt fractions of and . Assuming independent single effective lifetimes for non-prompt and production gives , while separating short- and long-lived contributions, assuming that the short-lived component is due to decays, gives , with the fraction of non-prompt produced via decays for GeV being . The distributions of the dipion invariant mass in the and decays are also measured and compared to theoretical predictions
Determination of spin and parity of the Higgs boson in the decay channel with the ATLAS detector
No full textSee paper for full list of authors – 42 pages plus author list + cover pages (59 pages total), 19 figures, 9 tables, submitted to The European Physical Journal C, All figures are available at https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/HIGG-2013-14/International audienceStudies of the spin and parity quantum numbers of the Higgs boson in the final state are presented, based on proton-proton collision data collected by the ATLAS detector at the Large Hadron Collider, corresponding to an integrated luminosity of 20.3 fb at a centre-of-mass energy of TeV. The Standard Model spin-parity hypothesis is compared with alternative hypotheses for both spin and CP. The case where the observed resonance is a mixture of the Standard-Model-like Higgs boson and CP-even () or CP-odd () Higgs boson in scenarios beyond the Standard Model is also studied. The data are found to be consistent with the Standard Model prediction and limits are placed on alternative spin and CP hypotheses, including CP mixing in different scenarios
Prompt and non-prompt J/ψ and ψ(2S) suppression at high transverse momentum in 5.02 TeV Pb+Pb collisions with the ATLAS experiment
No full textA measurement of J/ψ and ψ(2S) production is presented. It is based on a data sample from Pb+Pb collisions at sNN−−−√=5.02 TeV and pp collisions at s√=5.02 TeV recorded by the ATLAS detector at the LHC in 2015, corresponding to an integrated luminosity of 0.42 nb−1 and 25 pb−1 in Pb+Pb and pp, respectively. The measurements of per-event yields, nuclear modification factors, and non-prompt fractions are performed in the dimuon decay channel for 9<pμμT<40 GeV in dimuon transverse momentum, and −2<yμμ<2 in rapidity. Strong suppression is found in Pb+Pb collisions for both prompt and non-prompt J/ψ , increasing with event centrality. The suppression of prompt ψ(2S) is observed to be stronger than that of J/ψ , while the suppression of non-prompt ψ(2S) is equal to that of the non-prompt J/ψ within uncertainties, consistent with the expectation that both arise from b-quarks propagating through the medium. Despite prompt and non-prompt J/ψ arising from different mechanisms, the dependence of their nuclear modification factors on centrality is found to be quite similar
A measurement of the calorimeter response to single hadrons and determination of the jet energy scale uncertainty using LHC Run-1 -collision data with the ATLAS detector
No full textSee paper for full list of authors - 47 pages plus author list + cover pages (65 pages total), 38 figures, 1 table, submitted to Eur. Phys. J. C, All figures including auxiliary figures are available at http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/PERF-2015-05International audienceA measurement of the calorimeter response to isolated charged hadrons in the ATLAS detector at the LHC is presented. This measurement is performed with 3.2 nb of proton--proton collision data at TeV from 2010 and 0.1 nb of data at TeV from 2012. A number of aspects of the calorimeter response to isolated hadrons are explored. After accounting for energy deposited by neutral particles, there is a 5\% discrepancy in the modelling, using Geant4 physics lists, of the calorimeter response to isolated charged hadrons in the central calorimeter region. The description of the response to anti-protons at low momenta is found to be improved with respect to previous analyses. The electromagnetic and hadronic calorimeters are also examined separately, and the detector simulation is found to describe the response in the hadronic calorimeter well. The jet energy scale uncertainty and correlations in scale between jets of different momenta are derived based on these studies. The uncertainty is 2--5\% for jets with transverse momenta above 2 TeV, where this method provides the jet energy scale uncertainty for ATLAS
Study of the rare decays of B0s and B0 into muon pairs from data collected during the LHC Run 1 with the ATLAS detector
No full textSee paper for full list of authors - Comments: 29 pages plus author list + cover pages (46 pages total), 9 figures, 5 tables, submitted to Eur. Phys. J. C., regular article. All figures including auxiliary figures are available at this http URLInternational audienceA study of the decays B0→μ+μ− and B0s→μ+μ− has been performed using data corresponding to an integrated luminosity of 25 fb−1 of 7 TeV and 8 TeV proton--proton collisions collected with the ATLAS detector during the LHC Run 1. For B0, an upper limit on the branching fraction is set at B(B0→μ+μ−)<4.2×10−10 at 95% confidence level. For B0s, the branching fraction B(B0s→μ+μ−)=(0.9+1.1−0.8)×10−9 is measured. The results are consistent with the Standard Model expectation with a p-value of 4.8%, corresponding to 2.0 standard deviations
Measurement of the CP-violating phase phi(s) and the B-s(0) meson decay width difference with B-s(0) -> J/psi phi decays in ATLAS
No full textA measurement of the B-s(0) decay parameters in the B-s(0) -> J/psi/phi channel using an integrated luminosity of 14.3 fb(-1) collected by the ATLAS detector from 8TeV pp collisions at the LHC is presented. The measured parameters include the CP-violating phase phi(s), the decay width Gamma(s) and the width di ff erence between the mass eigenstates Delta Gamma(s). The values measured for the physical parameters are statistically combined with those from 4.9 fb-1 of 7TeV data, leading to the following: phi(s) = -0.090 +/- 0.078 (stat.) +/- 0.041 (syst.) rad Delta Gamma s = 0.085 +/- 0.011 (stat.) +/- 0.007 (syst.) ps(-1) Gamma(s) = 0.675 +/- 0.003 (stat.) +/- 0.003 (syst:) ps(-1). In the analysis the parameter Delta Gamma(s) is constrained to be positive. Results for phi(s) and Delta Gamma(s) are also presented as 68% and 95% likelihood contours in the phi(s)-Delta Gamma(s) plane. Also measured in this decay channel are the transversity amplitudes and corresponding strong phases. All measurements are in agreement with the Standard Model predictions
Search for a new resonance decaying to a or boson and a Higgs boson in the final states with the ATLAS Detector
No full textSee paper for full list of authors – 14 pages plus author list + cover pages (30 pages total), 4 figures, 1 tables, submitted to EPJC, All figures including auxiliary figures are available at http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/EXOT-2013-23/International audienceA search for a new resonance decaying to a or boson and a Higgs boson in the final states is performed using 20.3 fb of collision data recorded at 8 TeV with the ATLAS detector at the Large Hadron Collider. The search is conducted by examining the invariant mass distribution for a localized excess. No significant deviation from the Standard Model background prediction is observed. The results are interpreted in terms of constraints on the Minimal Walking Technicolor model and on a simplified approach based on a phenomenological Lagrangian of Heavy Vector Triplets
Search for bottom squark pair production in proton--proton collisions at 13 TeV with the ATLAS detector
No full textSee paper for full list of authors - 20 pages (plus author list: 37 pages total), 4 figures, 7 tables. Submitted to Eur. Phys. J. C. All figures including auxiliary figures are available at https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/SUSY-2015-01International audienceThe result of a search for pair production of the supersymmetric partner of the Standard Model bottom quark () is reported. The search uses 3.2 fb of collisions at 13 TeV collected by the ATLAS experiment at the Large Hadron Collider in 2015. Bottom squarks are searched for in events containing large missing transverse momentum and exactly two jets identified as originating from -quarks. No excess above the expected Standard Model background yield is observed. Exclusion limits at 95% confidence level on the mass of the bottom squark are derived in phenomenological supersymmetric -parity-conserving models in which the is the lightest squark and is assumed to decay exclusively via , where is the lightest neutralino. The limits significantly extend previous results; bottom squark masses up to 800 (840) GeV are excluded for the mass below 360 (100) GeV whilst differences in mass above 100 GeV between the and the are excluded up to a mass of 500 GeV
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