Search for Third Generation Scalar Leptoquarks Decaying into $\tau b$

We have searched for third generation leptoquarks (${\mathrm{LQ}}_3$) using $1.05{\mathrm{fb}}^{-1}$ of data collected with the D0 detector at the Fermilab Tevatron Collider operating at $\sqrt{s}=1.96\mathrm{TeV}$. We set a 95% C.L. lower limit of 210 GeV on the mass of a scalar ${\mathrm{LQ}}_3$ state decaying solely to a $b$ quark and a $\tau$ lepton.

Figure 1

Comparisons of data and the sum of backgrounds for (a) $p_T$ of the highest $p_T$ jet after preselection, (b) $m^{*}$ after preselection, and (c) $S_T$ for the 1 and $\ge 2$ $b$ tagged samples combined. We denote the diboson contribution as “db,” heavy quarks ($b$, $c$) as “hf,” and light partons ($u$, $d$, $s$, and gluons) as “lp.” The ${\mathrm{LQ}}_3$ signal is shown for $m_{{\mathrm{LQ}}_3}=200\mathrm{GeV}$, multiplied by 10 in (a) and (b) and without scaling in (c).

Figure 2

Observed and expected cross section limits at the 95% C.L. of the pair production of third generation leptoquarks as a function of $m_{{\mathrm{LQ}}_3}$. The uncertainty on the theoretical prediction is shown with shaded error bands. The theoretical cross section times branching ratio when $\beta =1/2$ is shown as the dashed line.