Search for third generation vector leptoquarks in $p\overline{p}$ collisions at $\sqrt{s}=1.96\mathrm{TeV}$

We search for a third generation vector leptoquark ($VLQ3$) that decays to a $b$ quark and tau lepton using the CDF II detector and $320{\mathrm{pb}}^{-1}$ of integrated luminosity from the Fermilab Tevatron. Observing a number of events in agreement with standard model expectations, we obtain, assuming Yang-Mills (minimal) couplings, the most stringent upper limit on the $VLQ3$ pair production cross section of 344 fb (493 fb) and lower limit on the $VLQ3$ mass of $317\mathrm{GeV}/c^2$ ($251\mathrm{GeV}/c^2$) at 95% C.L.

Figure 1

Distributions of $H_T$ for the (a) $e{\tau }_h$ channel and (b) $\mu {\tau }_h$ channel, including one of the control regions used for validation ($80<H_T<250\mathrm{GeV}$), and the regions used for the search ($H_T>250\mathrm{GeV}$). The individual background contributions are shown, as is a hypothetical signal with mass $m_{VLQ3}=320\mathrm{GeV}/c^2$, normalized to the data sample size.

Figure 2

The 95% C.L. upper limits on $\sigma (p\overline{p}\to VLQ3\overline{VLQ3})·{\beta }^2$ versus mass (lines with symbols), where $\beta \equiv \mathcal{B}(VLQ3\to b\tau )$. The theoretical expectations are shown for the Yang-Mills (solid line) and minimal (dashed line) couplings scenarios for the case $\beta =1$, with bands for uncertainties due to the choices of PDFs and $Q^2$. The dot-dashed and dotted curves show the threshold effect when the $VLQ3\to {\nu }_{\tau }t$ channel is open.