  We present the first experimental discrimination between the 2e/3 and 4e/3
top quark electric charge scenarios, using top quark pairs (ttbar) produced in
ppbar collisions at sqrt{s}=1.96 TeV by the Fermilab Tevatron collider. We use
370 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 bbar-quark
jets by using the charge and momenta of tracks within the jet cones. The data
is 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
QQbar with |q|=4e/3. We place an upper limit on the fraction of QQbar pairs fq
< 0.80 at the 90% C.L.
