We search for pair production of supersymmetric top quarks (${\tilde{t}}_1$), followed by $R$-parity violating decay ${\tilde{t}}_1\to \tau b$ with a branching ratio $\beta$, using $322{\mathrm{pb}}^{-1}$ of $p\overline{p}$ collisions at $\sqrt{s}=1.96\mathrm{TeV}$ collected by the upgraded Collider Detector at Fermilab. Two candidate events pass our final selection criteria, consistent with the standard model expectation. We set upper limits on the cross section $\sigma ({\tilde{t}}_1{\overline{\tilde{t}}}_1)\times {\beta }^2$ as a function of the top-squark mass $m({\tilde{t}}_1)$. Assuming $\beta =1$, we set a 95% confidence level limit $m({\tilde{t}}_1)>153\mathrm{GeV}/c^2$. The limits are also applicable to the case of a third-generation scalar leptoquark ($L{Q}_3$) decaying $L{Q}_3\to \tau b$.

• Received 27 February 2008
• Publisher error corrected 14 August 2008

DOI:https://doi.org/10.1103/PhysRevLett.101.071802