Bremsstrahlung of a quark propagating through a nucleus

The density of gluons produced in the central rapidity region of a heavy-io n collision is poorly known. We investigate the influence of the effects of quantum coherence on the transverse momentum distribution of photons and g luons radiated by a quark propagating through nuclear matter. We describe t he case where the radiation time substantially exceeds the nuclear radius ( the relevant case for RHIC and LHC energies), which is different from what is known as the Landau-Pomeranchuk-Migdal effect corresponding to an infini te medium. We find suppression of the radiation spectrum at small transvers e photon(gluon) momentum k(T), but enhancement for k(T)>1 GeV. Any nuclear effects vanish for k(T)greater than or equal to 10 GeV. Our results also al low us to calculate the k(T)-dependent nuclear effects in prompt photon, li ght, and heavy (Drell-Yan) dilepton and hadron production. [S0556-2813(99)0 5003-7].