Search for vector-like charge 2/3 T quarks in proton-proton collisions at sqrt(s) = 8 TeV

TL;DR

This paper reports a comprehensive search for vector-like T quarks with charge 2/3 in proton-proton collisions at 8 TeV, using multiple decay channels and setting new lower mass limits between 720 and 920 GeV.

Contribution

It introduces a multi-channel search strategy for T quarks at the LHC and establishes the most stringent mass limits to date for these particles.

Findings

No evidence of T quarks was observed in any channel.

Lower mass limits between 720 and 920 GeV were set at 95% confidence level.

Results improve upon previous limits for vector-like T quarks.

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.