Search for a Vector-like Quark with Charge 2/3 in t + Z Events from pp Collisions at sqrt(s) = 7 TeV

TL;DR

This paper reports a search for heavy vector-like T quarks decaying to top quarks and Z bosons in proton-proton collisions at 7 TeV, setting mass exclusion limits based on CMS detector data.

Contribution

First search for T quarks decaying to tZ in pp collisions at 7 TeV, establishing mass exclusion limits with CMS data.

Findings

No excess events observed beyond standard model background.

Excluded T quark masses below 475 GeV/c^2 at 95% confidence level.

Data consistent with background predictions.

Abstract

A search for pair-produced heavy vector-like charge-2/3 quarks, T, in pp collisions at a center-of-mass energy of 7 TeV, is performed with the CMS detector at the LHC. Events consistent with the flavor-changing-neutral-current decay of a T quark to a top quark and a Z boson are selected by requiring two leptons from the Z-boson decay, as well as an additional isolated charged lepton. In a data sample corresponding to an integrated luminosity of 1.14 inverse femtobarns, the number of observed events is found to be consistent with the standard model background prediction. Assuming a branching fraction of 100% for the decay T to tZ, a T quark with a mass less than 475 GeV/c^2 is excluded at the 95% confidence level.