Browsing by Author "Atlas Collaboration"
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Item Jet Reconstruction and Performance Using Particle Flow with the ATLAS Detector(Amer Physical Soc) Aaboud, M.; Aad, G.; Abbott, B.; Abdallah, J.; Abdinov, O.; Abeloos, B.; Aben, R.; Izen, Joseph M.; Leyton, Michael; Meirose, Bernhard; Namasivayam, Harisankar; Reeves, Kendall; Atlas Collaboration; 250674117 (Izen, JM); Izen, Joseph M.; Leyton, Michael; Meirose, Bernhard; Namasivayam, Harisankar; Reeves, KendallMeasurements of normalized differential cross sections of top quark pair tt̅ production are presented as a function of the mass, the transverse momentum and the rapidity of the tt̅ system in proton-proton collisions at center-of-mass energies of √s̅ = 7 and 8 TeV. The data set corresponds to an integrated luminosity of 4.6 fb⁻¹ at 7 TeV and 20.2 fb⁻¹ at 8 TeV, recorded with the ATLAS detector at the Large Hadron Collider. Events with top quark pair signatures are selected in the dilepton final state, requiring exactly two charged leptons and at least two jets with at least one of the jets identified as likely to contain a b hadron. The measured distributions are corrected for detector effects and selection efficiency to cross sections at the parton level. The differential cross sections are compared with different Monte Carlo generators and theoretical calculations of tt̅ production. The results are consistent with the majority of predictions in a wide kinematic range.Item Search for a Scalar Partner of the Top Quark in the Jets Plus Missing Transverse Momentum Final State at √s = 13 TeV with the ATLAS Detector(Springer, 2018-09-27) Aaboud, M.; Aad, G.; Abbott, B.; Abdinov, O.; Abeloos, B.; Abidi, S. H.; AbouZeid, O. S.; Izen, Joseph M.; Meirose, Bernhard; Reeves, Kendall; Atlas Collaboration; 250674117 (Izen, JM); Izen, Joseph M.; Meirose, Bernhard; Reeves, KendallA search for pair production of a scalar partner of the top quark in events with four or more jets plus missing transverse momentum is presented. An analysis of 36.1 fb⁻¹ of √s = 13 TeV proton-proton collisions collected using the ATLAS detector at the LHC yields no significant excess over the expected Standard Model background. To interpret the results a simplified supersymmetric model is used where the top squark is assumed to decay via t˜₁ → t((*)) χ˜₁⁰ and t˜₁ → bχ˜ (±)(1) → bW((*)) χ˜₁⁰, where χ˜₁⁰ (χ˜ (±)(1)) denotes the lightest neutralino (chargino). Exclusion limits are placed in terms of the top-squark and neutralino masses. Assuming a branching ratio of 100% to tχ˜₁⁰ top-squark masses in the range 450-1000 GeV are excluded for χ˜₁⁰ masses below 160 GeV. In the case where m(t˜)₁ ~ m(t) + m(χ˜₁⁰), top-squark masses in the range 235-590 GeV are excluded.Item Search for Heavy Resonances Decaying to a W or Z Boson and a Higgs Boson in the qq̅(′)bb̅ Final State in pp Collisions at √s =13 TeV with the ATLAS Detector(Elsevier Science Bv, 2018-09-27) Aaboud, M.; Aad, G.; Abbott, B.; Abdinov, O.; Abeloos, B.; Abidi, S. H.; AbouZeid, O. S.; Izen, Joseph M.; Meirose, Bernhard; Reeves, Kendall; Atlas Collaboration; 250674117 (Izen, JM); Izen, Joseph M.; Meirose, Bernhard; Reeves, KendallA search for heavy resonances decaying to a W or Z boson and a Higgs boson in the qq̅(′)bb̅ final state is described. The search uses 36.1 fb⁻¹ of proton-proton collision data at √s = 13 TeV collected by the ATLAS detector at the CERN Large Hadron Collider in 2015 and 2016. The data are in agreement with the Standard Model expectations, with the largest excess found at a resonance mass of 3.0 TeV with a local (global) significance of 3.3 (2.1) σ. The results are presented in terms of constraints on a simplified model with a heavy vector triplet. Upper limits are set on the production cross-section times branching ratio for resonances decaying to a W (Z) boson and a Higgs boson, itself decaying to bb̅, in the mass range between 1.1 and 3.8 TeV at 95% confidence level; the limits range between 83 and 1.6 fb (77 and 1.1 fb) at 95% confidence level.