Top FCNC induced by a Z ' boson

Abstract

We consider a Z' model in which the Z' boson couples only to up and top quarks. For a simple setup, one can consider a family-dependent U(1)' symmetry, under which only right-handed up-type quarks are charged. After symmetry breaking, the right-handed quarks mix with each other, and top flavor-changing neutral currents (FCNCs) mediated by the Z' boson can be generated at tree level. We take into account several processes at the parton level to probe the top FCNCs and find that the same-sign top quark pair production or the triple top quark production is the most capable of testing the top FCNCs. We also consider a few non-FCNC processes to probe the Z' boson, for example, dijet production at the LHC. Finally, we perform numerical analysis at detector level and find that the same-sign top quark pair production provides a much more stringent bound on the FCNC coupling than the other processes in most of the parameter space.