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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,045 records · Page 58
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DOE OSTI2012

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

A measurement of the production cross-section for top quark pairs ($t\bar{t}$) in pp collisions at $\sqrt{s} = 7TeV is presented using data recorded with the ATLAS detector at the Large Hadron Collider. Events are selected in the single lepton topology by requiring an electron or muon, large missing transverse momentum and at least three jets. With a data sample of 35 pb -1 , two different multivariate methods, one of which uses b-quark jet identification while the other does not, use kinematic variables to obtain cross-section measurements of σ $t\bar{t}$ = 187±11 (stat.) $+18\atop{-17}$ (syst.) ± 6 (lumi.) pb and σ $t\bar{t}$ =173 ± 17 (stat.) $+18\atop{-16}$ (syst.) ± 6 (lumi.) pb respectively. In conclusion, the two measurements are in agreement with each other and with QCD calculations. The first measurement has a better a priori sensitivity and constitutes the main result of this Letter.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Measurement of the top quark mass in the t t ¯ → dilepton channel from s = 8 TeV ATLAS data

The top quark mass is measured in the t¯t→dileptonchannel (lepton=e, μ) using ATLAS data recorded in the year 2012 at the LHC. The data were taken at a proton–proton centre-of-mass energy of √s=8TeVand correspond to an integrated luminosity of about 20.2fb-1. Exploiting the template method, and using the distribution of invariant masses of lepton–b-jetpairs, the top quark mass is measured to be mtop=172.99 ±0.41(stat)±0.74(syst)GeV, with a total uncertainty of 0.84GeV. Finally, acombination with previous ATLAS mtopmeasurements from √s=7TeVdata in the t¯t→dileptonand t¯t→lepton+jetschannels results in mtop=172.84 ±0.34(stat)±0.61(syst)GeV, with a total uncertainty of 0.70GeV.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

Search for high-mass new phenomena in the dilepton final state using proton–proton collisions at s = 13 TeV with the ATLAS detector

A search is conducted for both resonant and non-resonant high-mass new phenomena in dielectron and dimuon final states. The search uses 3.2 fb-1of proton–proton collision data, collected at √s = 13 TeV by the ATLAS experiment at the LHC in 2015. The dilepton invariant mass is used as the discriminating variable. No significant deviation from the Standard Model prediction is observed; therefore limits are set on the signal model parameters of interest at 95% credibility level. Upper limits are set on the cross-section times branching ratio for resonances decaying to dileptons, and the limits are converted into lower limits on the resonance mass, ranging between 2.74 TeV and 3.36 TeV, depending on the model. Lower limits on the ℓℓqq contact interaction scale are set between 16.7 TeV and 25.2 TeV, also depending on the model.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

Measurements of the charge asymmetry in top-quark pair production in the dilepton final state at s = 8 TeV with the ATLAS detector

We presented measurements of the top-antitop quark pair production charge asymmetry in the dilepton channel, characterized by two high- pT leptons (electrons or muons), using data corresponding to an integrated luminosity of 20.3 fb $-$1 from pp collisions at a center-of-mass energy $\sqrt{s}$ = 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 $t\bar{t}$ system are performed both in the full phase space and in a fiducial phase space closely matching the detector acceptance. Two observables are studied: A $ℓℓ\atop{C}$ based on the selected leptons and A$t\bar{t}\atop{C}$ based on the reconstructed $t\bar{t}$ final state. The inclusive asymmetries are measured in the full phase space to be A $ℓℓ\atop{C}$ = 0.008 ± 0.006 and A$t\bar{t}\atop{C}$= 0.021 ± 0.016 , which are in agreement with the Standard Model predictions of A $ℓℓ\atop{C}$ = 0.0064 ± 0.0003 and A$t\bar{t}\atop{C}$ = 0.0111 ± 0.0004 .

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

Measurement of exclusive γ γ → W + W - production and search for exclusive Higgs boson production in p p collisions at s = 8 TeV using the ATLAS detector

Searches for exclusively produced W boson pairs in the process p p ( γ γ ) → p W + W - p and an exclusively produced Higgs boson in the process p p ( g g ) → p H p have been performed using e ± μ ∓ final states. These measurements use 20.2 fb - 1 of p p collisions collected by the ATLAS experiment at a center-of-mass energy √ s = 8 TeV at the LHC. Exclusive production of W + W - consistent with the Standard Model prediction is found with 3.0 σ significance. The exclusive W + W - production cross section is determined to be σ ( γ γ → W + W - → e ± μ ∓ X ) = 6.9 ± 2.2 ( stat ) ± 1.4 ( sys ) fb , in agreement with the Standard Model prediction. Limits on anomalous quartic gauge couplings are set at 95% confidence level as - 1.7 × 10 - 6 < a W 0 / Λ 2 < 1.7 × 10 - 6 GeV - 2 and - 6.4 × 10 - 6 < a W C / Λ 2 < 6.3 × 10 - 6 GeV - 2 . A 95% confidence-level upper limit on the total production cross section for an exclusive Higgs boson is set to 1.2 pb.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

Search for pair production of Higgs bosons in the b b ¯ b b ¯ final state using proton-proton collisions at s = 13 TeV with the ATLAS detector with the ATLAS detector

A search for Higgs-boson pair production in the b b ¯ b b ¯ final state using proton-proton collisions at s = 13 TeV final state is carried out with 3.2 fb -1 of proton-proton collision data collected at √s=13 TeV with the ATLAS detector. The data are consistent with the estimated background and are used to set upper limits on the production cross section of Higgs-boson pairs times branching ratio to b b ¯ b b ¯ final state using proton-proton collisions at s = 13 TeV for both nonresonant and resonant production. In the case of resonant production of Kaluza-Klein gravitons within the Randall-Sundrum model, upper limits in the 24 to 91 fb range are obtained for masses between 600 and 3000 GeV, at the 95% confidence level. The production cross section times branching ratio for nonresonant Higgs-boson pairs is also constrained to be less than 1.22 pb, at the 95% confidence level.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

Measurement of the Inelastic Proton-Proton Cross Section at s = 13 TeV with the ATLAS Detector at the LHC

This Letter presents a measurement of the inelastic proton-proton cross section using 60 μ b -1 of p p collisions at a center-of-mass energy √ s of 13 TeV with the ATLAS detector at the LHC. Inelastic interactions are selected using rings of plastic scintillators in the forward region ( 2.07 < | η | < 3.86 ) of the detector. A cross section of 68.1 ± 1.4 mb is measured in the fiducial region ξ = M $2\atop{X}$ / s > 10 - 6 , where M X is the larger invariant mass of the two hadronic systems separated by the largest rapidity gap in the event. In this ξ range the scintillators are highly efficient. For diffractive events this corresponds to cases where at least one proton dissociates to a system with M X > 13 GeV . The measured cross section is compared with a range of theoretical predictions. When extrapolated to the full phase space, a cross section of 78.1 ± 2.9 mb is measured, consistent with the inelastic cross section increasing with center-of-mass energy.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

Muon reconstruction performance of the ATLAS detector in proton–proton collision data at √s=13 TeV

This article documents the performance of the ATLAS muon identification and reconstruction using the LHC dataset recorded at √s=13 TeV in 2015. Using a large sample of J/ψ → μμ and Z → μμ decays from 3.2 fb -1 of pp collision data, measurements of the reconstruction efficiency, as well as of the momentum scale and resolution, are presented and compared to Monte Carlo simulations. Furthermore, the reconstruction efficiency is measured to be close to 99% over most of the covered phase space (|η| < 2.5 and 52.2 , the p T resolution for muons from Z → μμ decays is 2.9% while the precision of the momentum scale for low-p T muons from J/ψ → μμ decays is about 0.2% .

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

The performance of the jet trigger for the ATLAS detector during 2011 data taking

The performance of the jet trigger for the ATLAS detector at the LHC during the 2011 data taking period is described. During 2011 the LHC provided proton–proton collisions with a centre-of-mass energy of 7 TeV and heavy ion collisions with a 2.76 TeV per nucleon–nucleon collision energy. The ATLAS trigger is a three level system designed to reduce the rate of events from the 40 MHz nominal maximum bunch crossing rate to the approximate 400 Hz which can be written to offline storage. The ATLAS jet trigger is the primary means for the online selection of events containing jets. Events are accepted by the trigger if they contain one or more jets above some transverse energy threshold. During 2011 data taking the jet trigger was fully efficient for jets with transverse energy above 25 GeV for triggers seeded randomly at Level 1. For triggers which require a jet to be identified at each of the three trigger levels, full efficiency is reached for offline jets with transverse energy above 60 GeV. Jets reconstructed in the final trigger level and corresponding to offline jets with transverse energy greater than 60 GeV, are reconstructed with a resolution in transverse energy with respect to offline jets, of better than 4 % in the central region and better than 2.5 % in the forward direction.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

Measurement of the $b\overline{b}$ dijet cross section in pp collisions at $\sqrt{s} = 7$ TeV with the ATLAS detector

The dijet production cross section for jets containing a b-hadron (b-jets) has been measured in proton–proton collisions with a centre-of-mass energy of √s = 7 TeV, using the ATLAS detector at the LHC. The data used correspond to an integrated luminosity of 4.2fb –1 . The cross section is measured for events with two identified b-jets with a transverse momentum p T > 20 GeV and a minimum separation in the η–Φ plane of ΔR=0.4. At least one of the jets in the event is required to have p T > 270 GeV. The cross section is measured differentially as a function of dijet invariant mass, dijet transverse momentum, boost of the dijet system, and the rapidity difference, azimuthal angle and angular distance between the b-jets. The results are compared to different predictions of leading order and next-to-leading order perturbative quantum chromodynamics matrix elements supplemented with models for parton-showers and hadronization.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

Measurements of ψ(2S) and X(3872) → J/ψπ + π - production in pp collisions at $\sqrt{s} = 8$ TeV with the ATLAS detector

Differential cross sections are presented for the prompt and non-prompt production of the hidden-charm states X(3872) and ψ(2S), in the decay mode J/ψπ + π – , measured using 11.4 fb –1 of pp collisions at √s = 8 TeV by the ATLAS detector at the LHC. The ratio of cross-sections X(3872)/ψ(2S) is also given, separately for prompt and non-prompt components, as well as the non-prompt fractions of X(3872) and ψ(2S). Assuming independent single effective lifetimes for non-prompt X(3872) and ψ(2S) production gives R B = B(B→X(3872)+any)B(X(3872)→J/ψπ+π–)/B(B→ψ(2S)+any)B(ψ(2S)→J/ψπ+π–)=(3.95±0.32(stat)±0.08(sys))×10 –2 separating short- and long-lived contributions, assuming that the short-lived component is due to B c decays, gives R B = (3.57 ± 0.33(stat) ± 0.11(sys)) × 10 –2 , with the fraction of non-prompt X(3872) produced via B c decays for p T (X(3872)) > 10 GeV being (25 ± 13(stat) ± 2(sys) ± 5(spin))%. The distributions of the dipion invariant mass in the X(3872) and ψ(2S) decays are also measured and compared to theoretical predictions.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗