Effects of Dense Matter on Hadron Production in Heavy-Ion Collisions
The intrinsic transverse momentum distribution of partons in the nucleon can be used to explain a large amount of high-pT hadron and photon production data in high-energy nucleon-nucleon collisions at energies √ s ≈ 20 to 1800 GeV. However, proton-nucleus experiments at energies ≈ 30 GeV show an extra enhancement (Cronin effect) in the yield of photons and mesons compared to a simple extrapolation of the proton-proton data. This enhancement is due to the effect of the dense hadronic matter encountered by the projectile proton in the nuclear environment. We discuss the origin and the properties of the nuclear enhancement.