Scaling properties of high <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" overflow="scroll"><mml:msub><mml:mi>p</mml:mi><mml:mi>T</mml:mi></mml:msub></mml:math> inclusive hadron production

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 pT, the invariant cross section exhibits a power-like behavior Ed3σ/d3p∝pT−n at fixed transverse x, xT=2|p→T|s, and fixed center-of-mass scattering angle θcm. Knowledge of the exponent n allows one to draw conclusions about the production mechanisms of hadrons, which are poorly known, even at high pT. We find that high-pT 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-pT 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-pT 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.

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