Bremsstrahlung of a quark propagating through a nucleus

The density of gluons produced in the central rapidity region of a heavy-ion collision is poorly known. We investigate the influence of the effects of quantum coherence on the transverse momentum distribution of photons and gluons radiated by a quark propagating through nuclear matter. We describe the 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 infinite medium. We find suppression of the radiation spectrum at small transverse photon(gluon) momentum $k_T,$ but enhancement for $k_T>1\mathrm{}\mathrm{GeV}.$ Any nuclear effects vanish for $k_T>~10\mathrm{GeV}.$ Our results also allow us to calculate the $k_T$-dependent nuclear effects in prompt photon, light, and heavy (Drell-Yan) dilepton and hadron production.