Search for the Flavor Changing Neutral Current Decay t $\to Zq$ in $p \bar{p}$ Collisions at $\sqrt{s}=1.96$

TL;DR

This paper searches for the rare flavor-changing neutral current decay of the top quark into a Z boson and a quark in proton-antiproton collisions, setting an upper limit on its occurrence due to its suppression in the standard model.

Contribution

First search for the top quark FCNC decay t→Zq at the Tevatron using the CDF II detector with a novel analysis method to discriminate signal from background.

Findings

Set an upper limit of 3.7% on the branching ratio of t→Zq at 95% confidence level.

Used 1.9 fb^{-1} of data from proton-antiproton collisions at 1.96 TeV.

Developed a kinematic analysis to distinguish FCNC signals from background events.

Abstract

We report a search for the flavor changing neutral current (FCNC) decay of the top quark \tZq ($q=u,c$) in \ppbar collisions at $\sqrt{s} = 1.96\tev$ using a data sample corresponding to an integrated luminosity of 1.9\invfb collected by the CDF II detector. This decay is strongly suppressed in the standard model (SM) and an observation of a signal at the Tevatron would be an indication of physics beyond the SM. Using $Z+\ge4$ jet final state candidate events, both with and without an identified bottom quark jet, we discriminate signal from background by exploiting kinematic constraints present in FCNC events and obtain an upper limit of $\btZq < 3.7%$ at 95% C.L.