Energy Loss of a Heavy Quark Produced in a Finite Size Medium

We study the medium-induced energy loss −∆E0(Lp) suffered by a heavy quark produced at initial time in a quark-gluon plasma, and escaping the plasma after travelling the distance Lp. The heavy quark is treated classically, and within the same framework −∆E0(Lp) consistently includes: the loss from standard collisional processes, initial bremsstrahlung due to the sudden acceleration of the quark, and transition radiation. The radiative loss induced by rescatterings −∆Erad(Lp) is not included in our study. For a ultrarelativistic heavy quark with momentum p & 10 GeV, and for a finite plasma with Lp . 5 fm, the loss −∆E0(Lp) is strongly suppressed compared to the stationary collisional contribution −∆Ecoll(Lp) ∝ Lp. Our results support that −∆Erad is the dominant contribution to the heavy quark energy loss (at least for Lp . 5 fm), as indeed assumed in most of jet-quenching analyses. However they might raise some question concerning the RHIC data on large p⊥ electron spectra.