Browsing by Author "Abouzeid, O. S."
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Item Determination of the Ratio of B -Quark Fragmentation Fractions F{s} / f{d} in pp Collisions at √s̅ =7 TeV with the ATLAS Detector(American Physical Society, 2015-12-30) Aad, G.; Abbott, B.; Abdallah, J.; Abdinov, O.; Aben, R.; Abolins, M.; Abouzeid, O. S.; Ahsan, Mahsana; Izen; Izen, Joseph M.; Leyton, Michael; Meirose, Bernhard; Namasivayam, Harisankar; Reeves, Kendall; ATLAS Collaboration; 250674117 (Izen, JM); 250674117 (Izen, JM); 250674117 (Izen, JM); Izen, Joseph M.; Leyton, Michael; Meirose, Bernhard; Namasivayam, Harisankar; Reeves, KendallWith an integrated luminosity of 2.47 fb⁻¹ recorded by the ATLAS experiment at the LHC, the exclusive decays B_s^0 → J/ψϕ and B_d^0 → J/ψK^{*0} of B mesons produced in pp collisions at √s̅ = 7 TeV are used to determine the ratio of fragmentation fractions f_s / f_d. From the observed B_s^0 → J/ψϕ and B_d^0 → J/ψK^{*0} yields, the quantity (f_s ± 0.017(th). This result is based on a new approach that provides a significant improvement of the world average / f_d) [ℬ(B_s^0 → J/ψϕ) /ℬ(B_d^0 → J/ψK^{*0})] is measured to be 0.199 ± 0.004 (stat) ± 0.008(syst). Using a recent theory prediction for [ℬ(B_s^0 → J/ψϕ) / ℬ(B_d^0 → J/ψK^{*0})] yields (f_s / f_d)=0.240 ± 0.004(stat) ± 0.010(syst).Item Measurement of Jet Charge in Dijet Events from √s̅ = 8 TeV pp Collisions with the ATLAS Detector(American Physical Society, 2016) Aad, G.; Abbott, B.; Abdallah, J.; Abdinov, O.; Aben, R.; Abolins, M.; Abouzeid, O. S.; Izen, Joseph M.; Leyton, Michael; Meirose, Bernhard; Namasivayam, Harisankar; Reeves, Kendall; 250674117 (Izen, JM); Izen, Joseph M.; Leyton, Michael; Meirose, Bernhard; Namasivayam, Harisankar; Reeves, KendallThe 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 √s̅ = 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.Item Measurement of the Correlation Between Flow Harmonics of Different Order in Lead-Lead Collisions at √s̅(NN) = 2.76 TeV with the ATLAS Detector(American Physical Society, 2015-09-14) Aad, G.; Abbott, B.; Abdallah, J.; Abdinov, O.; Aben, R.; Abolins, M.; Abouzeid, O. S.; Izen, Joseph M.; Leyton, Michael; Meirose, Bernhard; Namasivayam, Harisankar; Reeves, Kendall; ATLAS Collaboration; 250674117 (Izen, JM); 250674117 (Izen, JM); Izen, Joseph M.; Leyton, Michael; Meirose, Bernhard; Namasivayam, Harisankar; Reeves, KendallCorrelations between the elliptic or triangular flow coefficients ν_m (m=2 or 3) and other flow harmonics ν_n (n=2 to 5) are measured using \sqrt {s_{NN}}=2.76 TeV Pb+Pb collision data collected in 2010 by the ATLAS experiment at the LHC, corresponding to an integrated luminosity of 7 μb⁻¹. The ν_m - ν_n correlations are measured in midrapidity as a function of centrality, and, for events within the same centrality interval, as a function of event ellipticity or triangularity defined in a forward rapidity region. For events within the same centrality interval, ν₃ is found to be anticorrelated with ν₂ and this anticorrelation is consistent with similar anticorrelations between the corresponding eccentricities, ε₂ and ε₃. However, it is observed that ν₄ increases strongly with ν₂, and ν₅ increases strongly with both ν₂ and ν₃. The trend and strength of the ν_m-ν_n correlations for n=4 and 5 are found to disagree with ε_m-ε_n correlations predicted by initial-geometry models. Instead, these correlations are found to be consistent with the combined effects of a linear contribution to ν_n and a nonlinear term that is a function of v_2^2 or of v₂v₃, as predicted by hydrodynamic models. A simple two-component fit is used to separate these two contributions. The extracted linear and nonlinear contributions to ν₄ and ν₅ are found to be consistent with previously measured event-plane correlations.Item Measurements of the Top Quark Branching Ratios into Channels with Leptons and Quarks with the ATLAS Detector(American Physical Society, 2015-10-19) Aad, G.; Abbott, B.; Abdallah, J.; Abdinov, O.; Aben, R.; Abolins, M.; Abouzeid, O. S.; Izen, Joseph M.; Leyton, Michael; Meirose, Bernhard; Namasivayam, Harisankar; Reeves, Kendall; ATLAS Collaboration; 250674117 (Izen, JM); 250674117 (Izen, JM); Izen, Joseph M.; Leyton, Michael; Meirose, Bernhard; Namasivayam, Harisankar; Reeves, KendallMeasurements of the branching ratios of top quark decays into leptons and jets using events with tt̅ (top antitop) pairs are reported. Events were recorded with the ATLAS detector at the LHC in pp collisions at a center-of-mass energy of 7 TeV. The collected data sample corresponds to an integrated luminosity of 4.6 fb⁻¹. The measured top quark branching ratios agree with the Standard Model predictions within the measurement uncertainties of a few percentItem Measurements of the Total and Differential Higgs Boson Production Cross Sections Combining the H → γγ and H → ZZ^∗ → 4ℓ Decay Channels at √s̅ = 8 TeV with the ATLAS Detector(American Physical Society, 2015-08-27) Aad, G.; Abbott, B.; Abdallah, J.; Abdinov, O.; Aben, R.; Abolins, M.; Abouzeid, O. S.; Izen, Joseph M.; Leyton, Michael; Meirose, Bernhard; Namasivayam, Harisankar; Reeves, Kendall; 250674117 (Izen, JM); 250674117 (Izen, JM); Izen, Joseph M.; Leyton, Michael; Meirose, Bernhard; Namasivayam, Harisankar; Reeves, KendallMeasurements of the total and differential cross sections of Higgs boson production are performed using 20.3 fb⁻¹ of pp collisions produced by the Large Hadron Collider at a center-of-mass energy of √s̅ = 8 TeV and recorded by the ATLAS detector. Cross sections are obtained from measured H → γγ and H → ZZ^∗ → 4 ℓ event yields, which are combined accounting for detector efficiencies, fiducial acceptances, and branching fractions. Differential cross sections are reported as a function of Higgs boson transverse momentum, Higgs boson rapidity, number of jets in the event, and transverse momentum of the leading jet. The total production cross section is determined to be σ{pp → H} = 33.0 ± 5.3 (stat) ± 1.6 (syst) pb. The measurements are compared to state-of-the-art predictions. ©2015 CERN, for the ATLAS Collaboration. Published by the American Physical Society under the terms of the Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.Item Search for a Structure in the B{{_s}{^0}} Π^± Invariant Mass Spectrum with the ATLAS Experiment(Amer Physical Soc) 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 the narrow structure, X(5568), reported by the DO Collaboration in the decay sequence X → B{{_s}{^0}} π^±, B{{_s}{^0}} → J/ψφ, is presented. The analysis is based on a data sample recorded with the ATLAS detector at the LHC corresponding to 4.9 fb⁻¹ of pp collisions at 7 TeV and 19.5 fb⁻¹ at 8 TeV. No significant signal was found. Upper limits on the number of signal events, with properties corresponding to those reported by DO, and on the A production rate relative to B{{_s}{^0}} mesons, ρx, were determined at 95% confidence level. The results are N(X) < 382 and ρx < 0.015 for B{{_s}{^0}} mesons with transverse momenta above 10 GeV and N(X) < 356 and ρx < 0.016 for transverse momenta above 15 GeV. Limits are also set for potential B{{_s}{^0}} π^± resonances in the mass range 5550 to 5700 MeV.Item Search for B - L R-Parity-Violating Top Squarks in √s=13 TeV pp Collisions with the ATLAS Experiment(American Physical Society) 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 is presented for the direct pair production of the stop, the supersymmetric partner of the top quark, that decays through an R-parity-violating coupling to a final state with two leptons and two jets, at least one of which is identified as a b-jet. The data set corresponds to an integrated luminosity of 36.1 fb⁻¹ of proton-proton collisions at a center-of-mass energy of √s= 13 TeV, collected in 2015 and 2016 by the ATLAS detector at the LHC. No significant excess is observed over the Standard Model background, and exclusion limits are set on stop pair production at a 95% confidence level. Lower limits on the stop mass are set between 600 GeV and 1.5 TeV for branching ratios above 10% for decays to an electron or muon and a b-quark. © 2018 CERN, for the ATLAS Collaboration.Item Search for Electroweak Production of Supersymmetric Particles in Final States with Two or Three Leptons at √s = 13 TeV with the ATLAS Detector(Springer New York Llc, 2018-12-05) 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 the electroweak production of charginos, neutralinos and sleptons decaying into final states involving two or three electrons or muons is presented. The analysis is based on 36.1 fb⁻¹ of √s = 13 TeV proton– proton collisions recorded by the ATLAS detector at the Large Hadron Collider. Several scenarios based on simplified models are considered. These include the associated production of the next-to-lightest neutralino and the lightest chargino, followed by their decays into final states with leptons and the lightest neutralino via either sleptons or Standard Model gauge bosons; direct production of chargino pairs, which in turn decay into leptons and the lightest neutralino via intermediate sleptons; and slepton pair production, where each slepton decays directly into the lightest neutralino and a lepton. No significant deviations from the Standard Model expectation are observed and stringent limits at 95% confidence level are placed on the masses of relevant supersymmetric particles in each of these scenarios. For a massless lightest neutralino, masses up to 580 GeV are excluded for the associated production of the next-to-lightest neutralino and the lightest chargino, assuming gauge-boson mediated decays, whereas for slepton-pair production masses up to 500 GeV are excluded assuming three generations of mass-degenerate sleptons. © CERN for the benefit of the ATLAS collaboration 2018.Item Search for Heavy Higgs Bosons A / H Decaying to a Top Quark Pair in pp Collisions at √s̅ = 8 TeV with the ATLAS Detector(American Physical Society, 2018-05-15) 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, KendallSeveral extensions of the standard model predict associated production of dark-matter particles with a Higgs boson. Such processes are searched for in final states with missing transverse momentum and a Higgs boson decaying to a bb pair with the ATLAS detector using 36.1 fb-1 of pp collisions at a center-of-mass energy of 13 TeV at the LHC. The observed data are in agreement with the standard model predictions and limits are placed on the associated production of dark-matter particles and a Higgs boson.Item Search for Light Resonances Decaying to Boosted Quark Pairs and Produced in Association with a Photon or a Jet in Proton-Proton Collisions at √s=13 TeV with the ATLAS Detector(Elsevier Science B.V., 2018-11-02) 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, KendallThis Letter presents a search for new light resonances decaying to pairs of quarks and produced in association with a high-p_{T} photon or jet. The dataset consists of proton-proton collisions with an integrated luminosity of 36.1 fb⁻¹ at a centre-of-mass energy of √s = 13 TeV recorded by the ATLAS detector at the Large Hadron Collider. Resonance candidates are identified as massive large-radius jets with substructure consistent with a particle decaying into a quark pair. The mass spectrum of the candidates is examined for local excesses above background. No evidence of a new resonance is observed in the data, which are used to exclude the production of a lepto-phobic axial-vector Z′ boson.Item Search for Low-Mass Dijet Resonances Using Trigger-Level Jets with the ATLAS Detector in pp Collisions at √s =13 TeV(American Physical Society) 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, KendallSearches for dijet resonances with sub-TeV masses using the ATLAS detector at the Large Hadron Collider can be statistically limited by the bandwidth available to inclusive single-jet triggers, whose data-collection rates at low transverse momentum are much lower than the rate from standard model multijet production. This Letter describes a new search for dijet resonances where this limitation is overcome by recording only the event information calculated by the jet trigger algorithms, thereby allowing much higher event rates with reduced storage needs. The search targets low-mass dijet resonances in the range 450-1800 GeV. The analyzed data set has an integrated luminosity of up to 29.3 fb⁻¹ and was recorded at a center-of-mass energy of 13 TeV. No excesses are found; limits are set on Gaussian-shaped contributions to the dijet mass distribution from new particles and on a model of dark-matter particles with axial-vector couplings to quarks.Item Search for Magnetic Monopoles and Stable Particles with High Electric Charges in 8 TeV pp Collisions with the ATLAS Detector(American Physical Society, 2016-03-18) Aad, G.; Abbott, B.; Abdallah, J.; Abdinov, O.; Aben, R.; Abolins, M.; Abouzeid, O. S.; 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, KendallA search for highly ionizing particles produced in proton-proton collisions at 8 TeV center-of-mass energy is performed by the ATLAS Collaboration at the CERN Large Hadron Collider. The data set used corresponds to an integrated luminosity of 7.0 fb⁻¹. A customized trigger significantly increases the sensitivity, permitting a search for such particles with charges and energies beyond what was previously accessible. No events were found in the signal region, leading to production cross section upper limits in the mass range 200-2500 GeV for magnetic monopoles with magnetic charge in the range 0.5g_ D < |g| < 2.0g_D, where g_D is the Dirac charge, and for stable particles with electric charge in the range 10 < |z| < 60. Model-dependent limits are presented in given pair-production scenarios, and model-independent limits are presented in fiducial regions of particle energy and pseudorapidity.Item Search for Pair Production of a New Heavy Quark that Decays into a W Boson and a Light Quark in pp Collisions at √s̅ =8 TeV with the ATLAS Detector(American Physical Society, 2015-12-22) Aad, G.; Abbott, B.; Abdallah, J.; Abdinov, O.; Aben, R.; Abolins, M.; Abouzeid, O. S.; Izen, Joseph M.; Leyton, Michael; Meirose, Bernhard; Namasivayam, Harisankar; Reeves, Kendall; ATLAS Collaboration; 250674117 (Izen, JM); 250674117 (Izen, JM); Izen, Joseph M.; Leyton, Michael; Meirose, Bernhard; Namasivayam, Harisankar; Reeves, KendallA search is presented 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 √s̅ = 8 TeV collected by the ATLAS detector at the LHC. No evidence of QQ̅ production is observed. New chiral quarks with masses below 690 GeV are excluded at 95% confidence level, assuming BR(Q → Wq) = 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 → Wq) versus BR(Q → Hq).Item Search for Squarks and Gluinos in Final States with Jets and Missing Transverse Momentum Using 36 Fb⁻¹ of √s =13 TeV pp Collision Data with the ATLAS Detector(American Physical Society) 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 the supersymmetric partners of quarks and gluons (squarks and gluinos) in final states containing hadronic jets and missing transverse momentum, but no electrons or muons, is presented. The data used in this search were recorded in 2015 and 2016 by the ATLAS experiment in √s=13 TeV proton-proton collisions at the Large Hadron Collider, corresponding to an integrated luminosity of 36.1 fb⁻¹. The results are interpreted in the context of various models where squarks and gluinos are pair produced 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 2.03 TeV for a simplified model incorporating only a gluino 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 1.55 TeV are excluded if the lightest neutralino is massless. These limits substantially extend the region of supersymmetric parameter space previously excluded by searches with the ATLAS detector.Item Search for Supersymmetry in Events with Four or More Leptons in √s =13 TeV pp Collisions with ATLAS(American Physical Society) 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, KendallResults from a search for supersymmetry in events with four or more charged leptons (electrons, muons and taus) are presented. The analysis uses a data sample corresponding to 36.1 fb-1 of proton-proton collisions delivered by the Large Hadron Collider at s=13 TeV and recorded by the ATLAS detector. Four-lepton signal regions with up to two hadronically decaying taus are designed to target a range of supersymmetric scenarios that can be either enriched in or depleted of events involving the production and decay of a Z boson. Data yields are consistent with Standard Model expectations and results are used to set upper limits on the event yields from processes beyond the Standard Model. Exclusion limits are set at the 95% confidence level in simplified models of general gauge mediated supersymmetry, where Higgsino masses are excluded up to 295 GeV. In R-parity-violating simplified models with decays of the lightest supersymmetric particle to charged leptons, lower limits of 1.46, 1.06, and 2.25 TeV are placed on wino, slepton and gluino masses, respectively.Item Search for the Dimuon Decay of the Higgs Boson in pp Collisions at √s = 13 TeV with the ATLAS Detector(American Physical Society) 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; Izen, Joseph M.; Meirose, Bernhard; Reeves, KendallA search for heavy pseudoscalar (A) and scalar (H) Higgs bosons decaying into a top quark pair (tt̅) has been performed with 20.3 fb⁻¹ of proton-proton collision data collected by the ATLAS experiment at the Large Hadron Collider at a center-of-mass energy √s̅ = 8 TeV. Interference effects between the signal process and standard model tt production, which are expected to distort the signal shape from a single peak to a peak-dip structure, are taken into account. No significant deviation from the standard model prediction is observed in the tt̅ invariant mass spectrum in final states with an electron or muon, large missing transverse momentum, and at least four jets. The results are interpreted within the context of a type-II two-Higgs-doublet model. Exclusion limits on the signal strength are derived as a function of the mass m_{A/H} and the ratio of the vacuum expectation values of the two Higgs fields, tan β, for m_{A/H} > 500 GeV.Item Search for Top Squarks Decaying to Tau Sleptons in pp Collisions at √s =13 Te V with the ATLAS Detector(American Physical Society) Aaboud, M.; Aad, G.; Abbott, B.; Abdinov, O.; Abeloos, B.; Abidi, S. H.; Abouzeid, O. S.; Izen, Joseph M.; Meirose, Bernhard; Reeves, Kendall; 250674117 (Izen, JM); Izen, Joseph M.; Meirose, Bernhard; Reeves, KendallA search for direct pair production of top squarks in final states with two tau leptons, b-jets, and missing transverse momentum is presented. The analysis is based on proton-proton collision data at √s=13 TeV corresponding to an integrated luminosity of 36.1 fb⁻¹ recorded with the ATLAS detector at the Large Hadron Collider in 2015 and 2016. Two exclusive channels with either two hadronically decaying tau leptons or one hadronically and one leptonically decaying tau lepton are considered. No significant deviation from the Standard Model predictions is observed in the data. The analysis results are interpreted in terms of model-independent limits and used to derive exclusion limits on the masses of the top squark t̅~1 and the tau slepton τ~1 in a simplified model of supersymmetry with a nearly massless gravitino. In this model, masses up to m(t~1)=1.16 TeV and m(τ~1)=1.00 TeV are excluded at 95% confidence level. © 2018 CERN.Item Search for Vectorlike B Quarks in Events with One Isolated Lepton, Missing Transverse Momentum, and Jets at √s̅ = 8 TeV with the ATLAS Detector(Amer Physical Soc, 2015-06-19) Aad, G.; Abbott, B.; Abdallah, J.; Abdinov, O.; Aben, R.; Abolins, M.; Abouzeid, O. S.; Ahsan, Mahsana; 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, KendallA search has been performed for pair production of heavy vectorlike down-type (B) quarks. The analysis explores the lepton-plus-jets final state, characterized by events with one isolated charged lepton (electron or muon), significant missing transverse momentum, and multiple jets. One or more jets are required to be tagged as arising from b quarks, and at least one pair of jets must be tagged as arising from the hadronic decay of an electroweak boson. The analysis uses the full data sample of pp collisions recorded in 2012 by the ATLAS detector at the LHC, operating at a center-of-mass energy of 8 TeV, corresponding to an integrated luminosity of 20.3 fb⁻¹. No significant excess of events is observed above the expected background. Limits are set on vectorlike B production, as a function of the B branching ratios, assuming the allowable decay modes are B → Wt/Zb/Hb. In the chiral limit with a branching ratio of 100% for the decay B → Wt, the observed (expected) 95% C.L. lower limit on the vectorlike B mass is 810 GeV (760 GeV). In the case where the vectorlike B quark has branching ratio values corresponding to those of an SU(2) singlet state, the observed (expected) 95% C.L. lower limit on the vectorlike B mass is 640 GeV (505 GeV). The same analysis, when used to investigate pair production of a colored, charge 5/3 exotic fermion T{5/3}, with subsequent decay T{5/3} → Wt, sets an observed (expected) 95% C.L. lower limit on the T{5/3} mass of 840 GeV (780 GeV).Item Study of WWγ and WZγ Production in pp Collisions at √s̅ = 8 TeV and Search for Anomalous Quartic Gauge Couplings with the ATLAS Experiment(American Physical Society, 2018-05-15) Aaboud, M.; Aad, G.; Abbott, B.; Abdinov, O.; Abeloos, B.; Abidi, S. H.; Abouzeid, O. S.A search for the dimuon decay of the Higgs boson was performed using data corresponding to an integrated luminosity of 36.1 fb⁻¹ collected with the ATLAS detector in pp collisions at √s=13 TeV at the Large Hadron Collider. No significant excess is observed above the expected background. The observed (expected) upper limit on the cross section times branching ratio is 3.0 (3.1) times the Standard Model prediction at the 95% confidence level for a Higgs boson mass of 125 GeV. When combined with the pp collision data at √s=7 TeV and √s=8 TeV, the observed (expected) upper limit is 2.8 (2.9) times the Standard Model prediction.