Measurement of the correlation between flow harmonics of different order in lead-lead collisions at s NN = 2.76 TeV with the ATLAS detector
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Results for “Atlas”
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Measurement of differential J / ψ production cross sections and forward-backward ratios in p + Pb collisions with the ATLAS detector
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Search for chargino and neutralino production in final states with a Higgs boson and missing transverse momentum at s√=13 TeV with the ATLAS detector
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Search for direct stau production in events with two hadronic tau-leptons in root s=13 TeV pp collisions with the ATLAS detector
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Search for photonic signatures of gauge-mediated supersymmetry in 8 TeV p p collisions with the ATLAS detector
A search is presented for photonic signatures motivated by generalized models of gauge-mediated supersymmetry breaking. This search makes use of 20.3 fb -1 of proton-proton collision data at √s=8 TeV recorded by the ATLAS detector at the LHC, and explores models dominated by both strong and electroweak production of supersymmetric partner states. Four experimental signatures incorporating an isolated photon and significant missing transverse momentum are explored. These signatures include events with an additional photon, lepton, b-quark jet, or jet activity not associated with any specific underlying quark flavor. No significant excess of events is observed above the Standard Model prediction and model-dependent 95% confidence-level exclusion limits are set.
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Search for pair production of a new heavy quark that decays into a W boson and a light quark in p p collisions at s = 8 TeV with the ATLAS detector
We present a search for pair production of a new heavy quark ( Q ) that decays into a W boson and a light quark (q) in the final state where one W boson decays leptonically (to an electron or muon plus a neutrino) and the other W boson decays hadronically. The analysis is performed using an integrated luminosity of 20.3 fb -1 of pp collisions at $\sqrt{s}$ = 8 TeV collected by the ATLAS detector at the LHC. No evidence of $Q\overline{Q}$ production is observed. New chiral quarks with masses below 690 GeV are excluded at 95% confidence level, assuming BR ( Q → W q ) = 1 . Results are also interpreted in the context of vectorlike quark models, resulting in the limits on the mass of a vectorlike quark in the two-dimensional plane of BR ( Q → W q ) versus BR ( Q → H q ) .
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Measurement of the correlation between the polar angles of leptons from top quark decays in the helicity basis at $\sqrt{s}$ = 7 TeV using the ATLAS detector
A measurement of the correlations between the polar angles of leptons from the decay of pair-produced t and $\bar{t}$ quarks in the helicity basis is reported, using proton-proton collision data collected by the ATLAS detector at the LHC. The dataset corresponds to an integrated luminosity of 4.6 fb$^{-1}$ at a center-of-mass energy of $\sqrt{s}$ = 7 TeV collected during 2011. Candidate events are selected in the dilepton topology with large missing transverse momentum and at least two jets. The angles θ$_1$ and θ$_2$ between the charged leptons and the direction of motion of the parent quarks in the $t\bar{t}$ rest frame are sensitive to the spin information, and the distribution of cosθ$_1$ ∙ cosθ$_2$ is sensitive to the spin correlation between the t and $\bar{t}$ quarks. The distribution is unfolded to parton level and compared to the next-to-leading order prediction. A good agreement is observed.
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Measurement of jet charge in dijet events from $\sqrt{s}$ = 8 TeV pp collisions 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-weighted sums, called jet charge, in dijet events using 20.3 fb$^{-1}$ of data recorded with the ATLAS detector at $\sqrt{s}$ = 8 TeV in $pp$ collisions at the LHC. The jet charge distribution is unfolded to remove distortions from detector effects and the resulting particle-level distribution is compared with several models. The $p_T$ dependence of the jet charge distribution average and standard deviation are compared to predictions obtained with several leading-order and next-to-leading-order parton distribution functions. The data are also compared to different Monte Carlo simulations of QCD dijet production using various settings of the free parameters within these models. The chosen value of the strong coupling constant used to calculate gluon radiation is found to have a significant impact on the predicted jet charge. There is evidence for a $p_T$ dependence of the jet charge distribution for a given jet flavor. In agreement with perturbative QCD predictions, the data show that the average jet charge of quark-initiated jets decreases in magnitude as the energy of the jet increases.
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Measurements of W ± Z production cross sections in p p collisions at s = 8 TeV with the ATLAS detector and limits on anomalous gauge boson self-couplings
This paper presents measurements of W ± Z production in p p collisions at a center-of-mass energy of 8 TeV. The gauge bosons are reconstructed using their leptonic decay modes into electrons and muons. The data were collected in 2012 by the ATLAS experiment at the Large Hadron Collider and correspond to an integrated luminosity of 20.3 fb - 1 . The measured inclusive cross section in the detector fiducial region is σ W ± Z → ℓ ' ν ℓ ℓ = 35.1 ± 0.9 ( stat ) ± 0.8 ( sys ) ± 0.8 ( lumi ) fb , for one leptonic decay channel. In comparison, the next-to-leading-order Standard Model expectation is 30.0 ± 2.1 fb . Cross sections for W + Z and W - Z production and their ratio are presented as well as differential cross sections for several kinematic observables. Limits on anomalous triple gauge boson couplings are derived from the transverse mass spectrum of the W ± Z system. From the analysis of events with a W and a Z boson associated with two or more forward jets an upper limit at 95% confidence level on the W ± Z scattering cross section of 0.63 fb, for each leptonic decay channel, is established, while the Standard Model prediction at next-to-leading order is 0.13 ± 0.01 fb . Limits on anomalous quartic gauge boson couplings are also extracted.
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Search for the standard model Higgs boson produced in association with a vector boson and decaying into a tau pair in p p collisions at s = 8 TeV with the ATLAS detector
A search for the standard model Higgs boson produced in association with a vector boson with the decay H → τ τ is presented. The data correspond to 20.3 fb -1 of integrated luminosity from proton-proton collisions at √ s = 8 TeV recorded by the ATLAS experiment at the LHC during 2012.
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Measurements of Z γ and Z γ γ production in p p collisions at s = 8 TeV with the ATLAS detector
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Search for pair production of gluinos decaying via stop and sbottom in events with b -jets and large missing transverse momentum in p p collisions at s = 13 TeV with the ATLAS detector
A search for supersymmetry involving the pair production of gluinos decaying via third-generation squarks to the lightest neutralino ( χ$~0\atop{1}$ ) is reported. It uses an LHC proton-proton data set at a center-of-mass energy √ s = 13 TeV with an integrated luminosity of 3.2 fb -1 collected with the ATLAS detector in 2015. The signal is searched for in events containing several energetic jets, of which at least three must be identified as b jets, large missing transverse momentum, and, potentially, isolated electrons or muons. Large-radius jets with a high mass are also used to identify highly boosted top quarks. No excess is found above the predicted background. For χ$~0\atop{1}$ masses below approximately 700 GeV, gluino masses of less than 1.78 TeV and 1.76 TeV are excluded at the 95% C.L. in simplified models of the pair production of gluinos decaying via sbottom and stop, respectively. These results significantly extend the exclusion limits obtained with the √ s = 8 TeV data set.
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Search for new phenomena in final states with an energetic jet and large missing transverse momentum in p p collisions at s = 13 TeV using the ATLAS detector
We report results of a search for new phenomena in final states with an energetic jet and large missing transverse momentum. The search uses proton-proton collision data corresponding to an integrated luminosity of 3.2 fb $-$1 at $\sqrt{s}$ = 13 TeV collected in 2015 with the ATLAS detector at the Large Hadron Collider. Events are required to have at least one jet with a transverse momentum above 250 GeV and no leptons. Several signal regions are considered with increasing missing-transverse-momentum requirements between E$miss\atop{T}$ > 250 GeV and E$miss\atop{T}$ > 700 GeV . Good agreement is observed between the number of events in data and Standard Model predictions. The results are translated into exclusion limits in models with large extra spatial dimensions, pair production of weakly interacting dark-matter candidates, and the production of supersymmetric particles in several compressed scenarios.
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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 .
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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.
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Search for top squarks in final states with one isolated lepton, jets, and missing transverse momentum in s = 13 TeV p p collisions with the ATLAS detector
The results of a search for the top squark, the supersymmetric partner of the top quark, in final states with one isolated electron or muon, jets, and missing transverse momentum are reported. The search uses the 2015 LHC p p collision data at a center-of-mass energy of √ s = 13 TeV recorded by the ATLAS detector and corresponding to an integrated luminosity of 3.2 fb - 1 . The analysis targets two types of signal models: gluino-mediated pair production of top squarks with a nearly mass-degenerate top squark and neutralino and direct pair production of top squarks, decaying to the top quark and the lightest neutralino. The experimental signature in both signal scenarios is similar to that of a top quark pair produced in association with large missing transverse momentum. No significant excess over the Standard Model background prediction is observed, and exclusion limits on gluino and top squark masses are set at 95% confidence level. The results extend the LHC run-1 exclusion limit on the gluino mass up to 1460 GeV in the gluino-mediated scenario in the high gluino and low top squark mass region and add an excluded top squark mass region from 745 to 780 GeV for the direct top squark model with a massless lightest neutralino. The results are also reinterpreted to set exclusion limits in a model of vectorlike top quarks.
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Search for anomalous electroweak production of W W / W Z in association with a high-mass dijet system in p p collisions at s = 8 TeV with the ATLAS detector
A search is presented for anomalous quartic gauge boson couplings in vector-boson scattering. Here, the data for the analysis correspond to 20.2 fb -1 of √ 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 α 4 and α 5 are set by fitting the transverse mass of the diboson system, and the resulting 95% confidence intervals are - 0.024 < α 4 < 0.030 and - 0.028 < α 5 < 0.033 .
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Measurement of the t t ¯ production cross section in the τ + jets final state in p p collisions at s = 8 TeV using the ATLAS detector
A measurement of the inclusive p p → t $\bar{t}$ + X production cross section in the τ + jets final state using only the hadronic decays of the τ lepton is presented. The measurement is performed using 20.2 fb -1 of proton-proton collision data recorded at a center-of-mass energy of √ s = 8 TeV with the ATLAS detector at the Large Hadron Collider. The cross section is measured via a counting experiment by imposing a set of selection criteria on the identification and kinematic variables of the reconstructed particles and jets, and on event kinematic variables and characteristics. The production cross section is measured to be σ t $\bar{t}$ = 239 ± 29 pb , which is in agreement with the measurements in other final states and the theoretical predictions at this center-of-mass energy.
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