Experimental Discrimination between Charge $2e/3$ Top Quark and Charge $4e/3$ Exotic Quark Production Scenarios

We present the first experimental discrimination between the $2e/3$ and $4e/3$ top quark electric charge scenarios, using top quark pairs ($t\overline{t}$) produced in $p\overline{p}$ collisions at $\sqrt{s}=1.96\mathrm{TeV}$ by the Fermilab Tevatron Collider. We use $370{\mathrm{pb}}^{-1}$ of data collected by the D0 experiment and select events with at least one high transverse momentum electron or muon, high transverse energy imbalance, and four or more jets. We discriminate between $b$- and $\overline{b}$-quark jets by using the charge and momenta of tracks within the jet cones. The data are consistent with the expected electric charge, $|q|=2e/3$. We exclude, at the 92% C.L., that the sample is solely due to the production of exotic quark pairs $Q\overline{Q}$ with $|q|=4e/3$. We place an upper limit on the fraction of $Q\overline{Q}$ pairs $\rho <0.80$ at the 90% C.L.

Figure 1

(a) $b$ and $\overline{b}$ jet charge distributions derived from dijet data, (b) the 32 measured values of the top quark charge compared to the expected distributions in the SM and exotic cases, and (c) likelihood fit of the fraction of exotic quark pairs in the selected data sample.