  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.
