Abstract
A search for fermionic top quark partners T of charge 2/3 is presented. The search is carried out in proton-proton collisions corresponding to an integrated luminosity of 19.7 inverse femtobarns collected at a center-of-mass energy of sqrt(s) = 8 TeV with the CMS detector at the LHC. The T quarks are assumed to be produced strongly in pairs and can decay into tH, tZ, and bW. The search is performed in five exclusive channels: a single-lepton channel, a multilepton channel, two all-hadronic channels optimized either for the bW or the tH decay, and one channel in which the Higgs boson decays into two photons. The results are found to be compatible with the standard model expectations in all the investigated final states. A statistical combination of these results is performed and lower limits on the T quark mass are set. Depending on the branching fractions, lower mass limits between 720 and 920 GeV at 95% confidence level are found. These are among the strongest limits on vector-like T quarks obtained to date.
Highlights
The discovery of a Higgs boson with a mass of 125 GeV by the ATLAS [1] and CMS [2,3] collaborations motivates the search for exotic states involving the newly discovered particle
Nonsupersymmetric explanations are given by little Higgs models [4,5], models with extra dimensions [6,7], and composite Higgs models [6,7,8] in which the Higgs boson appears as a pseudo-NambuGoldstone boson [9]
Within the solenoid volume are a silicon pixel and strip tracker, a lead tungstate crystal electromagnetic calorimeter (ECAL), and a brass and scintillator hadron calorimeter (HCAL), each composed of a barrel and two endcap sections
Summary
The discovery of a Higgs boson with a mass of 125 GeV by the ATLAS [1] and CMS [2,3] collaborations motivates the search for exotic states involving the newly discovered particle. A fourth generation of chiral fermions, replicating one of the three generations of the SM with identical quantum numbers, is disfavored by electroweak fits within the framework of the SM [11] This is mostly because of large modifications of the Higgs production cross sections and branching fractions (B), if a single SM-like Higgs doublet is assumed. T quark searches by the CMS Collaboration [12,13,14] have assumed 100% branching fractions to various final states. One of the searches [15] is inclusive and sets limits for all possible branching fractions
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