Experimental discrimination between charge 2e/3 top quark and charge 4e/3 exotic quark production scenarios

Abstract

We present the first experimental discrimination between the 2e/3 and 4e/3 top quark electric charge scenarios, using top quark pairs (tt^- ) produced in pp^- collisions at √s=1.96 TeV by the Fermilab Tevatron Collider. We use 370pb^-1 of data collected by the D∅ 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 b̅-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 QQ̅ with |q|=4e/3. We place an upper limit on the fraction of QQ̅ pairs ρ <0.80 at the 90% C.L.