1,902 research outputs found
Search for dark matter in association with a Higgs boson decaying to b-quarks in pp collisions at s=13 TeV with the ATLAS detector
A search for dark matter pair production in association with a Higgs boson decaying to a pair of bottom quarks is presented, using 3.2 fbā1 of pp collisions at a centre-of-mass energy of 13 TeV collected by the ATLAS detector at the LHC. The decay of the Higgs boson is reconstructed as a high-momentum bbĀÆ system with either a pair of small-radius jets, or a single large-radius jet with substructure. The observed data are found to be consistent with the expected backgrounds. Results are interpreted using a simplified model with a Zā² gauge boson mediating the interaction between dark matter and the Standard Model as well as a two-Higgs-doublet model containing an additional Zā² boson which decays to a Standard Model Higgs boson and a new pseudoscalar Higgs boson, the latter decaying into a pair of dark matter particles
Search for resonances in the mass distribution of jet pairs with one or two jets identified as b-jets in protonāproton collisions at s=13Ā TeV with the ATLAS detector
Ā© 2016 The AuthorSearches for high-mass resonances in the dijet invariant mass spectrum with one or two jets identified as b-jets are performed using an integrated luminosity of 3.2Ā fbā1 of protonāproton collisions with a centre-of-mass energy of s=13Ā TeV recorded by the ATLAS detector at the Large Hadron Collider. No evidence of anomalous phenomena is observed in the data, which are used to exclude, at 95% credibility level, excited bā quarks with masses from 1.1 TeV to 2.1 TeV and leptophobic Zā² bosons with masses from 1.1 TeV to 1.5 TeV. Contributions of a Gaussian signal shape with effective cross sections ranging from approximately 0.4 to 0.001 pb are also excluded in the mass range 1.5ā5.0 TeV
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Z boson production in Pb+Pb collisions at āSnn = 5.02 TeV measured by the ATLAS experiment
The production yield of Z bosons is measured in the electron and muon decay channels in Pb+Pb collisions at āS = 5.02 TeV with the ATLAS detector. Data from the 2015 LHC run corresponding to an integrated luminosity of 0.49 nb are used for the analysis. The Z boson yield, normalised by the total number of minimum-bias events and the mean nuclear thickness function, is measured as a function of dilepton rapidity and event centrality. The measurements in Pb+Pb collisions are compared with similar measurements made in proton-proton collisions at the same centre-of-mass energy. The nuclear modification factor is found to be consistent with unity for all centrality intervals. The results are compared with theoretical predictions obtained at next-to-leading order using nucleon and nuclear parton distribution functions. The normalised Z boson yields in Pb+Pb collisions lie 1-3Ļ above the predictions. The nuclear modification factor measured as a function of rapidity agrees with unity and is consistent with a next-to-leading-order QCD calculation including the isospin effect. nn -
Search for flavour-changing neutral currents in processes with one top quark and a photon using 81 fbā1 of pp collisions at s=13TeV with the ATLAS experiment
A search for flavour-changing neutral current (FCNC) events via the coupling of a top quark, a photon, and an up or charm quark is presented using 81 fbā1 of protonāproton collision data taken at a centre-of-mass energy of 13 TeV with the ATLAS detector at the LHC. Events with a photon, an electron or muon, a b-tagged jet, and missing transverse momentum are selected. A neural network based on kinematic variables differentiates between events from signal and background processes. The data are consistent with the background-only hypothesis, and limits are set on the strength of the tqĪ³ coupling in an effective field theory. These are also interpreted as 95% CL upper limits on the cross section for FCNC tĪ³ production via a left-handed (right-handed) tuĪ³ coupling of 36 fb (78 fb) and on the branching ratio for tāĪ³u of 2.8Ć10ā5 (6.1Ć10ā5). In addition, they are interpreted as 95% CL upper limits on the cross section for FCNC tĪ³ production via a left-handed (right-handed) tcĪ³ coupling of 40 fb (33 fb) and on the branching ratio for tāĪ³c of 22Ć10ā5 (18Ć10ā5)
Measurement of J/Ļ production in association with a W Ā± boson with pp data at 8 TeV
A measurement of the production of a prompt J/Ļ meson in association with a WĀ± boson with WĀ± ā Ī¼Ī½ and J/Ļ ā Ī¼+Ī¼ā is presented for J/Ļ transverse momenta in the range 8.5ā150 GeV and rapidity |yJ/Ļ| < 2.1 using ATLAS data recorded in 2012 at the LHC. The data were taken at a proton-proton centre-of-mass energy of s = 8 TeV and correspond to an integrated luminosity of 20.3 fbā1. The ratio of the prompt J/Ļ plus WĀ± cross-section to the inclusive WĀ± cross-section is presented as a differential measurement as a function of J/Ļ transverse momenta and compared with theoretical predictions using different double-parton-scattering cross-sections. [Figure not available: see fulltext.]
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Measurement of Azimuthal Anisotropy of Muons from Charm and Bottom Hadrons in pp Collisions at sqrt[s]=13āāTeV with the ATLAS Detector.
The elliptic flow of muons from the decay of charm and bottom hadrons is measured in pp collisions at sqrt[s]=13āāTeV using a data sample with an integrated luminosity of 150āāpb^{-1} recorded by the ATLAS detector at the LHC. The muons from heavy-flavor decay are separated from light-hadron decay muons using momentum imbalance between the tracking and muon spectrometers. The heavy-flavor decay muons are further separated into those from charm decay and those from bottom decay using the distance-of-closest-approach to the collision vertex. The measurement is performed for muons in the transverse momentum range 4-7 GeV and pseudorapidity range |Ī·|<2.4. A significant nonzero elliptic anisotropy coefficient v_{2} is observed for muons from charm decays, while the v_{2} value for muons from bottom decays is consistent with zero within uncertainties
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