Search for flavor changing neutral currents in top quark decays in pp collisions at 7 TeV

TL;DR

This paper reports a search for flavor changing neutral currents in top quark decays at the LHC, finding no evidence and setting an upper limit on the decay branching fraction.

Contribution

First search for t to Zq FCNC decays in pp collisions at 7 TeV using CMS data, establishing new upper limits on the branching fraction.

Findings

No evidence for FCNC in top decays was observed.

A branching fraction greater than 0.21% is excluded at 95% confidence level.

The results are consistent with the Standard Model predictions.

Abstract

The results of a search for flavor changing neutral currents in top quark decays t to Zq in events with a topology compatible with the decay chain t t-bar to Wb + Zq to ell nu b + ell ell q are presented. The search is performed with a data sample corresponding to an integrated luminosity of 5.0 inverse femtobarns of proton-proton collisions at a center-of-mass energy of 7 TeV, collected with the CMS detector at the LHC. The observed number of events agrees with the standard model prediction and no evidence for flavor changing neutral currents in top quark decays is found. A t to Zq branching fraction greater than 0.21% is excluded at the 95% confidence level.