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Publication Metadata only Search for squarks and gluinos in final states with jets and missing transverse momentum at √s = 13 TeV with the ATLAS detector(Springer, 2016) Aaboud, M.; Aad, Georges; Abbott, Brad K.; Abdallah, Jalal Mohamad; Abdinov, O. B.; Abeloos, Baptiste; Aben, R.; AbouZeid, O. S.; Abraham, Nicola L.; Abramowicz, Halina; Aaboud, M., Université Mohammed Premier Oujda, Oujda, Morocco; Aad, Georges, Aix Marseille Université, Marseille, France; Abbott, Brad K., Homer L. Dodge Department of Physics and Astronomy, The University of Oklahoma, Norman, United States; Abdallah, Jalal Mohamad, University of Iowa, Iowa City, United States; Abdinov, O. B., Azerbaijan National Academy of Sciences, Baku, Azerbaijan; Abeloos, Baptiste, Laboratoire de l'Accélérateur Linéaire, Orsay, France; Aben, R., Universiteit van Amsterdam, Amsterdam, Netherlands; AbouZeid, O. S., Santa Cruz Institute for Particle Physics, Santa Cruz, United States; Abraham, Nicola L., University of Sussex, Brighton, United Kingdom; Abramowicz, Halina, Raymond and Beverly Sackler School of Physics and Astronomy, Tel Aviv University, Tel Aviv-Yafo, IsraelA search for squarks and gluinos in final states containing hadronic jets, missing transverse momentum but no electrons or muons is presented. The data were recorded in 2015 by the ATLAS experiment in √s = 13 TeV proton-proton collisions at the Large Hadron Collider. No excess above the Standard Model background expectation was observed in 3.2 fb−1 of analyzed data. Results are interpreted within simplified models that assume R-parity is conserved and the neutralino is the lightest supersymmetric particle. An exclusion limit at the 95 % confidence level on the mass of the gluino is set at 1.51 TeV for a simplified model incorporating only a gluino octet and the lightest neutralino, assuming the lightest neutralino is massless. For a simplified model involving the strong production of mass-degenerate first- and second-generation squarks, squark masses below 1.03 TeV are excluded for a massless lightest neutralino. These limits substantially extend the region of supersymmetric parameter space excluded by previous measurements with the ATLAS detector. © 2019 Elsevier B.V., All rights reserved.Publication Metadata only Measurement of event-shape observables in Z → ℓ+ℓ− events in pp collisions at √ s = 7 TeV with the ATLAS detector at the LHC(Springer New York LLC barbara.b.bertram@gsk.com, 2016) Aad, Georges; Abbott, Brad K.; Abdallah, Jalal Mohamad; Abdinov, O. B.; Abeloos, Baptiste; Aben, R.; Abolins, Maris A.; AbouZeid, O. S.; Abraham, Nicola L.; Abramowicz, Halina; Aad, Georges, Centre de Physique des Particules de Marseille, Marseille, France; Abbott, Brad K., Homer L. Dodge Department of Physics and Astronomy, The University of Oklahoma, Norman, United States; Abdallah, Jalal Mohamad, Institute of Physics, Academia Sinica, Institute Of Physics, Taipei, Taiwan; Abdinov, O. B., Azerbaijan National Academy of Sciences, Baku, Azerbaijan; Abeloos, Baptiste, Laboratoire de l'Accélérateur Linéaire, Orsay, France; Aben, R., Universiteit van Amsterdam, Amsterdam, Netherlands; Abolins, Maris A., Department of Physics and Astronomy, Michigan State University, East Lansing, United States; AbouZeid, O. S., Santa Cruz Institute for Particle Physics, Santa Cruz, United States; Abraham, Nicola L., Department of Physics and Astronomy, University of Sussex, Brighton, United Kingdom; Abramowicz, Halina, Raymond and Beverly Sackler School of Physics and Astronomy, Tel Aviv University, Tel Aviv-Yafo, IsraelEvent-shape observables measured using charged particles in inclusive Z-boson events are presented, using the electron and muon decay modes of the Z bosons. The measurements are based on an integrated luminosity of 1.1 fb−1 of proton-proton collisions recorded by the ATLAS detector at theLHCat a centre-of-mass energy √ s = 7TeV.Chargedparticle distributions, excluding the lepton-antilepton pair from the Z-boson decay, are measured in different ranges of transverse momentum of the Z boson. Distributions include multiplicity, scalar sum of transverse momenta, beam thrust, transverse thrust, spherocity, and F-parameter, which are in particular sensitive to properties of the underlying event at small values of the Z-boson transverse momentum. The measured observables are compared with predictions from Pythia 8, Sherpa, and Herwig7. Typically, all three Monte Carlo generators provide predictions that are in better agreement with the data at high Z-boson transverse momenta than at low Z-boson transverse momenta, and for the observables that are less sensitive to the number of charged particles in the event. © 2017 Elsevier B.V., All rights reserved.Publication Metadata only Charged-particle distributions in pp interactions at √s = 8 TeV measured with the ATLAS detector(Springer Science and Business Media Deutschland GmbH, 2016) Aad, Georges; Abbott, Brad K.; Abdallah, Jalal Mohamad; Abdinov, O. B.; Abeloos, Baptiste; Aben, R.; Abolins, Maris A.; AbouZeid, O. S.; Abraham, Nicola L.; Abramowicz, Halina; Aad, Georges, Centre de Physique des Particules de Marseille, Marseille, France; Abbott, Brad K., The University of Oklahoma, Norman, United States; Abdallah, Jalal Mohamad, Academia Sinica, Institute Of Physics, Taipei, Taiwan; Abdinov, O. B., Azerbaijan National Academy of Sciences, Baku, Azerbaijan; Abeloos, Baptiste, Laboratoire de l'Accélérateur Linéaire, Orsay, France; Aben, R., Universiteit van Amsterdam, Amsterdam, Netherlands; Abolins, Maris A., Department of Physics and Astronomy, Michigan State University, East Lansing, United States; AbouZeid, O. S., Santa Cruz Institute for Particle Physics, Santa Cruz, United States; Abraham, Nicola L., University of Sussex, Brighton, United Kingdom; Abramowicz, Halina, Tel Aviv University, Tel Aviv-Yafo, IsraelThis paper presents measurements of distributions of charged particles which are produced in proton-proton collisions at a centre-of-mass energy of √s = 8 TeV and recorded by the ATLAS detector at the LHC. A special dataset recorded in 2012 with a small number of interactions per beam crossing (below 0.004) and corresponding to an integrated luminosity of 160 µb-1 was used. A minimum-bias trigger was utilised to select a data sample of more than 9 million collision events. The multiplicity, pseudorapidity, and transverse momentum distributions of charged particles are shown in different regions of kinematics and chargedparticle multiplicity, including measurements of final states at high multiplicity. The results are corrected for detector effects and are compared to the predictions of various Monte Carlo event generator models which simulate the full hadronic final state. © 2024 Elsevier B.V., All rights reserved.Publication Metadata only Search for scalar leptoquarks in pp collisions at √S = 13TeV with the ATLAS experiment(Institute of Physics, 2016) Aaboud, M.; Aad, Georges; Abbott, Brad K.; Abdallah, Jalal Mohamad; Abdinov, O. B.; Abeloos, Baptiste; Aben, R.; AbouZeid, O. S.; Abraham, Nicola L.; Abramowicz, Halina; Aaboud, M., Faculty of Science, Université Mohammed Premier Oujda, Oujda, Morocco; Aad, Georges, Centre de Physique des Particules de Marseille, Marseille, France; Abbott, Brad K., The University of Oklahoma, Norman, United States; Abdallah, Jalal Mohamad, University of Iowa, Iowa City, United States; Abdinov, O. B., Azerbaijan National Academy of Sciences, Baku, Azerbaijan; Abeloos, Baptiste, Laboratoire de l'Accélérateur Linéaire, Orsay, France; Aben, R., Universiteit van Amsterdam, Amsterdam, Netherlands; AbouZeid, O. S., Santa Cruz Institute for Particle Physics, Santa Cruz, United States; Abraham, Nicola L., University of Sussex, Brighton, United Kingdom; Abramowicz, Halina, Tel Aviv University, Tel Aviv-Yafo, IsraelAn inclusive search for a new-physics signature of lepton-jet resonances has been performed by the ATLAS experiment. Scalar leptoquarks, pair-produced in pp collisions at s √S13 TeV at the large hadron collider, have been considered. An integrated luminosity of 3.2 fb−1, corresponding to the full 2015 dataset was used. First (second) generation leptoquarks were sought in events with two electrons (muons) and two or more jets. The observed event yield in each channel is consistent with Standard Model background expectations. The observed (expected) lower limits on the leptoquark mass at 95% confidence level are 1100 and 1050 GeV (1160 and 1040 GeV) for first and second generation leptoquarks, respectively, assuming a branching ratio into a charged lepton and a quark of 100%. Upper limits on the aforementioned branching ratio are also given as a function of leptoquark mass. Compared with the results of earlier ATLAS searches, the sensitivity is increased for leptoquark masses above 860 GeV, and the observed exclusion limits confirm and extend the published results. © 2022 Elsevier B.V., All rights reserved.Publication Metadata only Measurement of the total cross section from elastic scattering in pp collisions at √s=8 TeV with the ATLAS detector(Elsevier B.V., 2016) Aaboud, M.; Aad, Georges; Abbott, Brad K.; Abdallah, Jalal Mohamad; Abdinov, O. B.; Abeloos, Baptiste; Aben, R.; AbouZeid, O. S.; Abraham, Nicola L.; Abramowicz, Halina; Aaboud, M., Université Mohammed Premier Oujda, Oujda, Morocco; Aad, Georges, Aix Marseille Université, Marseille, France; Abbott, Brad K., Homer L. Dodge Department of Physics and Astronomy, The University of Oklahoma, Norman, United States; Abdallah, Jalal Mohamad, University of Iowa, Iowa City, United States; Abdinov, O. B., Azerbaijan National Academy of Sciences, Baku, Azerbaijan; Abeloos, Baptiste, Laboratoire de l'Accélérateur Linéaire, Orsay, France; Aben, R., Universiteit van Amsterdam, Amsterdam, Netherlands; AbouZeid, O. S., Santa Cruz Institute for Particle Physics, Santa Cruz, United States; Abraham, Nicola L., Department of Physics and Astronomy, University of Sussex, Brighton, United Kingdom; Abramowicz, Halina, Raymond and Beverly Sackler School of Physics and Astronomy, Tel Aviv University, Tel Aviv-Yafo, IsraelA measurement of the total pp cross section at the LHC at s=8 TeV is presented. An integrated luminosity of 500 μb−1 was accumulated in a special run with high-β⋆ beam optics to measure the differential elastic cross section as a function of the Mandelstam momentum transfer variable t. The measurement is performed with the ALFA sub-detector of ATLAS. Using a fit to the differential elastic cross section in the −t range from 0.014 GeV2 to 0.1 GeV2 to extrapolate t→0, the total cross section, σtot(pp→X), is measured via the optical theorem to be σtot(pp→X)=96.07±0.18(stat.)±0.85(exp.)±0.31(extr.)mb, where the first error is statistical, the second accounts for all experimental systematic uncertainties and the last is related to uncertainties in the extrapolation t→0. In addition, the slope of the exponential function describing the elastic cross section at small t is determined to be B=19.74±0.05(stat.)±0.23(syst.)GeV−2. © 2019 Elsevier B.V., All rights reserved.Publication Metadata only Search for the Standard Model Higgs boson decaying into bb¯ produced in association with top quarks decaying hadronically in pp collisions at √s = 8 TeV with the ATLAS detector(Springer Verlag service@springer.de, 2016) The Atlas Collaboration; Aad, Georges; Abbott, Brad K.; Abdallah, Jalal Mohamad; Abdinov, O. B.; Abeloos, Baptiste; Aben, R.; Abolins, Maris A.; AbouZeid, O. S.; Abraham, Nicola L.; The Atlas Collaboration, null, Organisation Européenne pour la Recherche Nucléaire, Geneva, Switzerland; Aad, Georges, Centre de Physique des Particules de Marseille, Marseille, France; Abbott, Brad K., Homer L. Dodge Department of Physics and Astronomy, The University of Oklahoma, Norman, United States; Abdallah, Jalal Mohamad, University of Iowa, Iowa City, United States; Abdinov, O. B., Azerbaijan National Academy of Sciences, Baku, Azerbaijan; Abeloos, Baptiste, Laboratoire de l'Accélérateur Linéaire, Orsay, France; Aben, R., Universiteit van Amsterdam, Amsterdam, Netherlands; Abolins, Maris A., Department of Physics and Astronomy, Michigan State University, East Lansing, United States; AbouZeid, O. S., Santa Cruz Institute for Particle Physics, Santa Cruz, United States; Abraham, Nicola L., Department of Physics and Astronomy, University of Sussex, Brighton, United KingdomA search for Higgs boson production in association with a pair of top quarks (tt¯ H) is performed, where the Higgs boson decays to bb¯, and both top quarks decay hadronically. The data used correspond to an integrated luminosity of 20.3 fb−1 of pp collisions at √s = 8 TeV collected with the ATLAS detector at the Large Hadron Collider. The search selects events with at least six energetic jets and uses a boosted decision tree algorithm to discriminate between signal and Standard Model background. The dominant multijet background is estimated using a dedicated data-driven technique. For a Higgs boson mass of 125 GeV, an upper limit of 6.4 (5.4) times the Standard Model cross section is observed (expected) at 95% confidence level. The best-fit value for the signal strength is μ = 1.6 ± 2.6 times the Standard Model expectation for mH = 125 GeV. Combining all tt¯ H searches carried out by ATLAS at √s = 8 and 7 TeV, an observed (expected) upper limit of 3.1 (1.4) times the Standard Model expectation is obtained at 95% confidence level, with a signal strength μ = 1.7 ± 0.8. © 2019 Elsevier B.V., All rights reserved.Publication Metadata only Muon reconstruction performance of the ATLAS detector in proton–proton collision data at s=13 TeV(Springer Science and Business Media, LLC, 2016) Atlas Collaboration; Aad, Georges; Abbott, Brad K.; Abdallah, Jalal Mohamad; Abdinov, O. B.; Abeloos, Baptiste; Aben, R.; Abolins, Maris A.; AbouZeid, O. S.; Abraham, Nicola L.; Atlas Collaboration, null, Organisation Européenne pour la Recherche Nucléaire, Geneva, Switzerland; Aad, Georges, Centre de Physique des Particules de Marseille, Marseille, France; Abbott, Brad K., The University of Oklahoma, Norman, United States; Abdallah, Jalal Mohamad, University of Iowa, Iowa City, United States; Abdinov, O. B., Azerbaijan National Academy of Sciences, Baku, Azerbaijan; Abeloos, Baptiste, Laboratoire de l'Accélérateur Linéaire, Orsay, France; Aben, R., Universiteit van Amsterdam, Amsterdam, Netherlands; Abolins, Maris A., Department of Physics and Astronomy, Michigan State University, East Lansing, United States; AbouZeid, O. S., Santa Cruz Institute for Particle Physics, Santa Cruz, United States; Abraham, Nicola L., University of Sussex, Brighton, United KingdomThis 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. The reconstruction efficiency is measured to be close to 99% over most of the covered phase space (| η| < 2.5 and 5 < pT< 100 GeV). The isolation efficiency varies between 93 and 100% depending on the selection applied and on the momentum of the muon. Both efficiencies are well reproduced in simulation. In the central region of the detector, the momentum resolution is measured to be 1.7% (2.3%) for muons from J/ ψ→ μμ (Z→ μμ) decays, and the momentum scale is known with an uncertainty of 0.05%. In the region | η| > 2.2 , the pT resolution for muons from Z→ μμ decays is 2.9% while the precision of the momentum scale for low-pT muons from J/ ψ→ μμ decays is about 0.2%. © 2024 Elsevier B.V., All rights reserved.Publication Metadata only Beam-induced and cosmic-ray backgrounds observed in the ATLAS detector during the LHC 2012 proton-proton running period(Institute of Physics Publishing helen.craven@iop.org, 2016) Aad, Georges; Abbott, Brad K.; Abdallah, Jalal Mohamad; Abdinov, O. B.; Abeloos, Baptiste; Aben, R.; Abolins, Maris A.; AbouZeid, O. S.; Abraham, Nicola L.; Abramowicz, Halina; Aad, Georges, Centre de Physique des Particules de Marseille, Marseille, France; Abbott, Brad K., Homer L. Dodge Department of Physics and Astronomy, The University of Oklahoma, Norman, United States; Abdallah, Jalal Mohamad, University of Iowa, Iowa City, United States; Abdinov, O. B., Azerbaijan National Academy of Sciences, Baku, Azerbaijan; Abeloos, Baptiste, Laboratoire de l'Accélérateur Linéaire, Orsay, France; Aben, R., Universiteit van Amsterdam, Amsterdam, Netherlands; Abolins, Maris A., Department of Physics and Astronomy, Michigan State University, East Lansing, United States; AbouZeid, O. S., Santa Cruz Institute for Particle Physics, Santa Cruz, United States; Abraham, Nicola L., University of Sussex, Brighton, United Kingdom; Abramowicz, Halina, Raymond and Beverly Sackler School of Physics and Astronomy, Tel Aviv University, Tel Aviv-Yafo, IsraelThis paper discusses various observations on beam-induced and cosmic-ray backgrounds in the ATLAS detector during the LHC 2012 proton-proton run. Building on published results based on 2011 data, the correlations between background and residual pressure of the beam vacuum are revisited. Ghost charge evolution over 2012 and its role for backgrounds are evaluated. New methods to monitor ghost charge with beam-gas rates are presented and observations of LHC abort gap population by ghost charge are discussed in detail. Fake jets from colliding bunches and from ghost charge are analysed with improved methods, showing that ghost charge in individual radio-frequency buckets of the LHC can be resolved. Some results of two short periods of dedicated cosmic-ray background data-taking are shown, in particular cosmic-ray muon induced fake jet rates are compared to Monte Carlo simulations and to the fake jet rates from beam background. A thorough analysis of a particular LHC fill, where abnormally high background was observed, is presented. Correlations between backgrounds and beam intensity losses in special fills with very high β∗ are studied. © 2019 Elsevier B.V., All rights reserved.Publication Metadata only Search for new phenomena in events with a photon and missing transverse momentum in pp collisions at √s = 13 TeV with the ATLAS detector(Springer Verlag service@springer.de, 2016) The Atlas Collaboration; Aaboud, M.; Aad, Georges; Abbott, Brad K.; Abdallah, Jalal Mohamad; Abdinov, O. B.; Abeloos, Baptiste; Aben, R.; AbouZeid, O. S.; Abraham, Nicola L.; The Atlas Collaboration, null, Organisation Européenne pour la Recherche Nucléaire, Geneva, Switzerland; Aaboud, M., Université Mohammed Premier Oujda, Oujda, Morocco; Aad, Georges, Centre de Physique des Particules de Marseille, Marseille, France; Abbott, Brad K., Homer L. Dodge Department of Physics and Astronomy, The University of Oklahoma, Norman, United States; Abdallah, Jalal Mohamad, University of Iowa, Iowa City, United States; Abdinov, O. B., Azerbaijan National Academy of Sciences, Baku, Azerbaijan; Abeloos, Baptiste, Laboratoire de l'Accélérateur Linéaire, Orsay, France; Aben, R., Universiteit van Amsterdam, Amsterdam, Netherlands; AbouZeid, O. S., Santa Cruz Institute for Particle Physics, Santa Cruz, United States; Abraham, Nicola L., Department of Physics and Astronomy, University of Sussex, Brighton, United KingdomResults of a search for new phenomena in events with an energetic photon and large missing transverse momentum with the ATLAS experiment at the Large Hadron Collider are reported. The data were collected in proton-proton collisions at a centre-of-mass energy of 13 TeV and correspond to an integrated luminosity of 3.2 fb−1. The observed data are in agreement with the Standard Model expectations. Exclusion limits are presented in models of new phenomena including pair production of dark matter candidates or large extra spatial dimensions. In a simplified model of dark matter and an axial-vector mediator, the search excludes mediator masses below 710 GeV for dark matter candidate masses below 150 GeV. In an effective theory of dark matter production, values of the suppression scale M∗ up to 570 GeV are excluded and the effect of truncation for various coupling values is reported. For the ADD large extra spatial dimension model the search places more stringent limits than earlier searches in the same event topology, excluding MD up to about 2.3 (2.8) TeV for two (six) additional spatial dimensions, the limits are reduced by 20-40% depending on the number of additional spatial dimensions when applying a truncation procedure. © 2019 Elsevier B.V., All rights reserved.Publication Metadata only Measurement of the charged-particle multiplicity inside jets from √s = 8 TeV pp collisions with the ATLAS detector(Springer Science and Business Media, LLC, 2016) Atlas Collaboration; Aad, Georges; Abbott, Brad K.; Abdallah, Jalal Mohamad; Abdinov, O. B.; Abeloos, Baptiste; Aben, R.; Abolins, Maris A.; AbouZeid, O. S.; Abraham, Nicola L.; Atlas Collaboration, null, Organisation Européenne pour la Recherche Nucléaire, Geneva, Switzerland; Aad, Georges, Centre de Physique des Particules de Marseille, Marseille, France; Abbott, Brad K., The University of Oklahoma, Norman, United States; Abdallah, Jalal Mohamad, Academia Sinica, Institute Of Physics, Taipei, Taiwan; Abdinov, O. B., Azerbaijan National Academy of Sciences, Baku, Azerbaijan; Abeloos, Baptiste, Laboratoire de l'Accélérateur Linéaire, Orsay, France; Aben, R., Universiteit van Amsterdam, Amsterdam, Netherlands; Abolins, Maris A., Department of Physics and Astronomy, Michigan State University, East Lansing, United States; AbouZeid, O. S., Santa Cruz Institute for Particle Physics, Santa Cruz, United States; Abraham, Nicola L., University of Sussex, Brighton, United KingdomThe number of charged particles inside jets is a widely used discriminant for identifying the quark or gluon nature of the initiating parton and is sensitive to both the perturbative and non-perturbative components of fragmentation. This paper presents a measurement of the average number of charged particles with >500 pT> 500 {\mathrm{MeV}} MeV inside high-momentum jets in dijet events using 20.3 fb-1 of data recorded with the ATLAS detector in pp collisions at √s = 8 TeV collisions at the LHC. The jets considered have transverse momenta from 50 GeV up to and beyond 1.5 TeV. The reconstructed charged-particle track multiplicity distribution is unfolded to remove distortions from detector effects and the resulting charged-particle multiplicity is compared to several models. Furthermore, quark and gluon jet fractions are used to extract the average charged-particle multiplicity for quark and gluon jets separately. © 2024 Elsevier B.V., All rights reserved.