Analysis of events with b-jets and a pair of leptons of the same charge in pp collisions at s = 8 $$ \sqrt{s}=8 $$ TeV with the ATLAS detector

Abstract

Analysis of events with b-jets and a pair of leptons of the same charge in pp collisions at √ s = 8 TeV with the ATLAS detectorThe ATLAS collaboration E-mail: atlas.publications@cern.chAbstract: An analysis is presented of events containing jets including at least one btagged jet, sizeable missing transverse momentum, and at least two leptons including a pair of the same electric charge, with the scalar sum of the jet and lepton transverse momenta being large. A data sample with an integrated luminosity of 20.3 fb −1 of pp collisions at √ s = 8 TeV recorded by the ATLAS detector at the Large Hadron Collider is used. Standard Model processes rarely produce these final states, but there are several models of physics beyond the Standard Model that predict an enhanced rate of production of such events; the ones considered here are production of vector-like quarks, enhanced fourtop-quark production, pair production of chiral b -quarks, and production of two positively charged top quarks. Eleven signal regions are defined; subsets of these regions are combined when searching for each class of models. In the three signal regions primarily sensitive to positively charged top quark pair production, the data yield is consistent with the background expectation. There are more data events than expected from background in the set of eight signal regions defined for searching for vector-like quarks and chiral b -quarks, but the significance of the discrepancy is less than two standard deviations. The discrepancy reaches 2.5 standard deviations in the set of five signal regions defined for searching for four-top-quark production. The results are used to set 95% CL limits on various models. The ATLAS collaboration 35 IntroductionThe Standard Model (SM) has been repeatedly confirmed experimentally. Nonetheless there is a need for physics beyond the SM (BSM) at about the TeV scale, with additional features that explain the baryon asymmetry of the universe, specify the nature of dark matter, and provide a mechanism to naturally stabilize the Higgs boson mass at its observed value of approximately 125 GeV [1,2]. This paper reports on a search for BSM physics resulting in pairs of isolated high-transverse-momentum (high-p T ) leptons 1 with the same electric charge, hereafter denoted as same-sign leptons, (or three or more leptons of any charge) missing transverse momentum, and b-jets. This is a promising search channel since the SM yields of such events are small, and several types of BSM physics may contribute. Among the models that predict enhanced same-sign lepton production are those that postulate the existence of vector-like quarks, an enhancement of the four-top-quark production cross section, the existence of a fourth generation of chiral quarks, or production of two positively charged top quarks. A common data sample is used to search for each of 1 Only electrons and muons are considered in the search. Tau leptons are not explicitly reconstructed, but electrons and muons from τ decay may enter the selected samples. Table ...

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