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 Landau-Pomeranchuk effect (LPE) on the transverse momentum distribution of photons and gluons radiated by a quark propagating through nuclear matter. We describe the case that the radiation time substantially exceeds the nuclear radius (which is the relevant case for RHIC and LHC energies). We find LPE suppression of the radiation spectrum at small transverse photon/gluon momentum kT , but LPE enhancement for kT > 1GeV. The LPE enhancement vanishes for kT ≥ 10GeV. Our results allow also to calculate the kT dependent nuclear effects in prompt photon, light and heavy (Drell-Yan) dilepton and hadron production. PACS numbers: 12.38.Bx, 12.38.Aw, 24.85.+p, 25.75.-q