Scaling properties of high pT inclusive hadron production

Abstract

We analyze the scaling properties of inclusive hadron production in proton-proton and in heavy ion collisions from fixed target to collider energies. At large transverse momentum p{sub T}, the invariant cross section exhibits a power-like behavior Ed{sup 3}{sigma}/d{sup 3}p {proportional_to} p{sub T}{sup -n} at fixed transverse x, x{sub T} = 2|{bar p}{sub T}|/{radical}s, and fixed center-of-mass scattering angle {theta}{sub cm}. Knowledge of the exponent n allows one to draw conclusions about the production mechanisms of hadrons, which are poorly known, even at high p{sub T}. We find that high-p{sub T} hadrons are produced by different mechanisms at fixed-target and collider energies. For pions, higher-twist subprocesses where the pion is produced directly dominate at fixed target energy, while leading-twist partonic scattering plus fragmentation is the most important mechanism at collider energies. High-p{sub T} baryons on the other hand appear to be produced by higher-twist mechanisms at all available energies. The higher-twist mechanism of direct proton production can be verified experimentally by testing whether high p{sub T} protons are produced as single hadrons without accompanying secondaries. In addition, we find that medium-induced gluon radiation in heavy ion collisions can violate scaling.