Direct measurement of the top quark charge at hadron colliders

We consider photon radiation in $\overline{t}t$ events at the upgraded Fermilab Tevatron and the CERN Large Hadron Collider (LHC) as a tool to measure the electric charge of the top quark. We analyze the contributions of $\overline{t}t\gamma$ production and radiative top quark decays to $p\stackrel{\left(-\right)}{p}\to \gamma l^{\pm }\nu \overline{b}bjj,$ assuming that both b quarks are tagged. With $20\hspace{0.5em}{\mathrm{fb}}^{-1}$ at the Tevatron, the possibility that the “top quark” discovered in run I is actually an exotic charge $-4/3$ quark can be ruled out at the ∼95% confidence level. At the CERN LHC, it will be possible to determine the charge of the top quark with an accuracy of about 10%.