Search for vectorlike charge 2 / 3 T quarks in proton-proton collisions at √ ( s ) = 8 TeV

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 fb − 1 collected at a center-of-mass energy of √ 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 t H , t Z , and b W . The search is performed in five exclusive channels: a single-lepton channel, a multilepton channel, two all-hadronic channels optimized either for the b W or the t H 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 vectorlike T quarks obtained to date.