Search for flavor-changing neutral currents in top quark decays at ATLAS

TL;DR

This paper reports on a search for flavor-changing neutral currents in top quark decays at the LHC, using leptonic final states to set limits on the rare decay mode $t ightarrow qZ$, with results consistent with Standard Model backgrounds.

Contribution

First search at ATLAS for top quark FCNC decays to $qZ$ in leptonic final states, establishing new upper limits on the branching ratio.

Findings

No significant excess over background observed.

Set upper limit on $t ightarrow qZ$ branching ratio.

Results are consistent with Standard Model predictions.

Abstract

ATLAS results are presented on a search for flavor-changing neutral currents (FCNC) in top quark decays at the LHC. Events are searched for where a pair of top quarks is produced and one decays through the Standard Model $t \rightarrow Wb$ mode while the other decays through the FCNC mode $t \rightarrow qZ$. Leptonic final states are used in which both the $W$- and $Z$-bosons decay leptonically, yielding final states with three leptons and two jets. The observed events are consistent with the expected backgrounds from Drell-Yan and diboson production and a limit on the FCNC branching ratio of top quarks to $qZ$ is set.