2,810 research outputs found
Measurement of the cross-section and charge asymmetry of bosons produced in proton-proton collisions at TeV with the ATLAS detector
This paper presents measurements of the and cross-sections and the associated charge asymmetry as a
function of the absolute pseudorapidity of the decay muon. The data were
collected in proton--proton collisions at a centre-of-mass energy of 8 TeV with
the ATLAS experiment at the LHC and correspond to a total integrated luminosity
of 20.2~\mbox{fb^{-1}}. The precision of the cross-section measurements
varies between 0.8% to 1.5% as a function of the pseudorapidity, excluding the
1.9% uncertainty on the integrated luminosity. The charge asymmetry is measured
with an uncertainty between 0.002 and 0.003. The results are compared with
predictions based on next-to-next-to-leading-order calculations with various
parton distribution functions and have the sensitivity to discriminate between
them.Comment: 38 pages in total, author list starting page 22, 5 figures, 4 tables,
submitted to EPJC. All figures including auxiliary figures are available at
https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/STDM-2017-13
Search for chargino-neutralino production with mass splittings near the electroweak scale in three-lepton final states in âs=13âTeV pp collisions with the ATLAS detector
A search for supersymmetry through the pair production of electroweakinos with mass splittings near the electroweak scale and decaying via on-shell W and Z bosons is presented for a three-lepton final state. The analyzed proton-proton collision data taken at a center-of-mass energy of âs=13ââTeV were collected between 2015 and 2018 by the ATLAS experiment at the Large Hadron Collider, corresponding to an integrated luminosity of 139ââfbâ1. A search, emulating the recursive jigsaw reconstruction technique with easily reproducible laboratory-frame variables, is performed. The two excesses observed in the 2015â2016 data recursive jigsaw analysis in the low-mass three-lepton phase space are reproduced. Results with the full data set are in agreement with the Standard Model expectations. They are interpreted to set exclusion limits at the 95% confidence level on simplified models of chargino-neutralino pair production for masses up to 345 GeV
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Measurement of Azimuthal Anisotropy of Muons from Charm and Bottom Hadrons in pp Collisions at sqrt[s]=13ââTeV 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]=13ââTeV using a data sample with an integrated luminosity of 150ââpb^{-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 |η|<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
Search for flavour-changing neutral currents in processes with one top quark and a photon using 81 fbâ1 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 fbâ1 of protonâproton 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 tqÎł coupling in an effective field theory. These are also interpreted as 95% CL upper limits on the cross section for FCNC tÎł production via a left-handed (right-handed) tuÎł coupling of 36 fb (78 fb) and on the branching ratio for tâÎłu of 2.8Ă10â5 (6.1Ă10â5). In addition, they are interpreted as 95% CL upper limits on the cross section for FCNC tÎł production via a left-handed (right-handed) tcÎł coupling of 40 fb (33 fb) and on the branching ratio for tâÎłc of 22Ă10â5 (18Ă10â5)
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Z boson production in Pb+Pb collisions at âSnn = 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 âS = 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 1-3Ï 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 -
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Combination of searches for Higgs boson pairs in pp collisions at s=13TeV with the ATLAS detector
This letter presents a combination of searches for Higgs boson pair production using up to 36.1 fbâ1 of protonâproton collision data at a centre-of-mass energy s=13 TeV recorded with the ATLAS detector at the LHC. The combination is performed using six analyses searching for Higgs boson pairs decaying into the bbÂŻbbÂŻ, bbÂŻW+Wâ, bbÂŻÏ+Ïâ, W+WâW+Wâ, bb¯γγ and W+Wâγγ final states. Results are presented for non-resonant and resonant Higgs boson pair production modes. No statistically significant excess in data above the Standard Model predictions is found. The combined observed (expected) limit at 95% confidence level on the non-resonant Higgs boson pair production cross-section is 6.9 (10) times the predicted Standard Model cross-section. Limits are also set on the ratio (Îșλ) of the Higgs boson self-coupling to its Standard Model value. This ratio is constrained at 95% confidence level in observation (expectation) to â5.0<Îșλ<12.0 (â5.8<Îșλ<12.0). In addition, limits are set on the production of narrow scalar resonances and spin-2 KaluzaâKlein RandallâSundrum gravitons. Exclusion regions are also provided in the parameter space of the habemus Minimal Supersymmetric Standard Model and the Electroweak Singlet Model
Measurement of VH, HâbbÂŻ production as a function of the vector-boson transverse momentum in 13 TeV pp collisions with the ATLAS detector
Cross-sections of associated production of a Higgs boson decaying into bottom-quark pairs and an electroweak gauge boson, W or Z, decaying into leptons are measured as a function of the gauge boson transverse momentum. The measurements are performed in kinematic fiducial volumes defined in the `simplified template cross-sectionÂŽ framework. The results are obtained using 79.8 fbâ1 of proton-proton collisions recorded by the ATLAS detector at the Large Hadron Collider at a centre-of-mass energy of 13 TeV. All measurements are found to be in agreement with the Standard Model predictions, and limits are set on the parameters of an effective Lagrangian sensitive to modifications of the Higgs boson couplings to the electroweak gauge bosons.Fil: Aaboud, M.. UniversitĂ© Mohamed; MarruecosFil: Aad, G.. Aix-Marseille UniversitĂ©; Francia. Centre National de la Recherche Scientifique; FranciaFil: Abbott, B.. University of Oklahoma; Estados UnidosFil: Abbott, D. C.. University of Oklahoma; Estados UnidosFil: Abdinov, O.. Azerbaijan Academy of Sciences; AzerbaiyĂĄnFil: Abed Abud, A.. Universita degli Studi di Pavia; Italia. Istituto Nazionale di Fisica Nucleare; ItaliaFil: Abhayasinghe, D. K.. Royal Holloway University of London; Reino UnidoFil: Abidi, S. H.. University of Toronto; CanadĂĄFil: AbouZeid, O. S.. Universidad de Copenhagen; DinamarcaFil: Abraham, N. L.. University of Sussex; Reino UnidoFil: Abramowicz, H.. Universitat Tel Aviv; IsraelFil: Abreu, H.. Technion - Israel Institute of Technology; IsraelFil: Abulaiti, Y.. Argonne National Laboratory; Estados UnidosFil: Acharya, B. S.. Istituto Nazionale di Fisica Nucleare; Italia. The Abdus Salam. International Centre for Theoretical Physics; Italia. Kingâs College London; Reino UnidoFil: Adachi, S.. University of Tokyo; JapĂłnFil: Adam, L.. UniversitĂ€t Mainz; AlemaniaFil: Adam Bourdarios, C.. UniversitĂ© Paris-Sud; Francia. Universite Paris-Saclay; . Centre National de la Recherche Scientifique; FranciaFil: Adamczyk, L.. University of Science and Technology; PoloniaFil: Adamek, L.. University of Toronto; CanadĂĄFil: Adelman, J.. Northern Illinois University; Estados UnidosFil: Adersberger, M.. Ludwig-Maximilians-UniversitĂ€t MĂŒnchen; AlemaniaFil: Adiguzel, A.. Bogazici University; TurquĂa. Istanbul University; TurquĂaFil: Adorni, S.. UniversitĂ© de GenĂšve; FranciaFil: Adye, T.. Rutherford Appleton Laboratory; Reino UnidoFil: Affolder, A. A.. University of California Santa Cruz; Estados UnidosFil: Afik, Y.. Technion - Israel Institute of Technology; IsraelFil: Agapopoulou, C.. UniversitĂ© Paris-Sud; Francia. Centre National de la Recherche Scientifique; Francia. Universite Paris-Saclay;Fil: Agaras, M. N.. UniversitĂ© Clermont Auvergne; Francia. Centre National de la Recherche Scientifique; FranciaFil: Aggarwal, A.. Radboud Universiteit Nijmegen; PaĂses BajosFil: Arduh, Francisco Anuar. Cern - European Organization for Nuclear Research; Suiza. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - La Plata. Instituto de FĂsica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de FĂsica La Plata; Argentin
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Search for Magnetic Monopoles and Stable High-Electric-Charge Objects in 13 Tev Proton-Proton Collisions with the ATLAS Detector.
A search for magnetic monopoles and high-electric-charge objects is presented using 34.4ââfb^{-1} of 13 TeV pp collision data collected by the ATLAS detector at the LHC during 2015 and 2016. The considered signature is based upon high ionization in the transition radiation tracker of the inner detector associated with a pencil-shape energy deposit in the electromagnetic calorimeter. The data were collected by a dedicated trigger based on the tracker high-threshold hit capability. The results are interpreted in models of Drell-Yan pair production of stable particles with two spin hypotheses (0 and 1/2) and masses ranging from 200 to 4000 GeV. The search improves by approximately a factor of 5 the constraints on the direct production of magnetic monopoles carrying one or two Dirac magnetic charges and stable objects with electric charge in the range 20â€|z|â€60 and extends the charge range to 60<|z|â€100
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