We report a search for the flavor-changing neutral-current decay of the top quark $t\to Zq$ ($q=u$, $c$) in $p\overline{p}$ collisions at $\sqrt{s}=1.96\mathrm{TeV}$ using a data sample corresponding to an integrated luminosity of $1.9{\mathrm{fb}}^{-1}$ collected by the CDF II detector. This decay is strongly suppressed in the standard model and an observation of a signal at the Fermilab Tevatron would be an indication of physics beyond the standard model. Using $Z+\ge 4$ jet final state candidate events, with and without an identified bottom quark jet, we obtain an upper limit of $\mathcal{B}(t\to Zq)<3.7\%$ at 95% C.L.

• Received 15 May 2008

DOI:https://doi.org/10.1103/PhysRevLett.101.192002