Flavor changing neutral currents in ttbar decays at D\O

TL;DR

This paper searches for flavor changing neutral currents in top quark decays at the DØ experiment, setting upper limits on the branching ratio of such decays using 4.1 fb$^{-1}$ of data from proton-antiproton collisions.

Contribution

It provides the first limits on the branching ratio of top quark FCNC decays to Z and a light quark at the Tevatron, assuming anomalous couplings.

Findings

No evidence of FCNC in top decays was observed.

Set a 95% confidence level upper limit of 3.2% on B(t→Zq).

Constraints on anomalous $tuZ$ and $tcZ$ couplings were derived.

Abstract

We present a search for flavor changing neutral currents (FCNC) in decays of top quarks. The analysis is based on a search for $t\bar{t}\rightarrow\ell'\nu\ell\bar{\ell}$+jets ($\ell, \ell' = e,\mu$) final states using 4.1 {\rm fb}$^{-1}$ of integrated luminosity of $p\bar{p}$ collisions at $\sqrt{s} = 1.96$ {\rm TeV}. We extract limits on the branching ratio $B(t\rightarrow Zq)$ ($q = u, c$ quarks), assuming anomalous $tuZ$ or $tcZ$ couplings. We do not observe any sign of such anomalous coupling and set a limit of $B < 3.2%$ at 95% C.L.