Radiative energy loss of high energy partons traversing an expanding QCD plasma

We study analytically the medium-induced energy loss of a high energy parton passing through a finite size QCD plasma, which is expanding longitudinally according to Bjorken's model. We extend the Baier-Dokshitzer-Mueller-Peigne-Schiff formalism already applied to static media to the case of a quark which hits successive layers of matter of decreasing temperature, and we show that the resulting radiative energy loss can be as large as 6 times the corresponding one in a static plasma at the reference temperature T = T(L), which is reached after the quark propagates a distance L.