Average $p_t$ as a probe of high energy QCD dynamics

Abstract

Average transverse momentum of hadrons produced in high energy collisions is proposed as a diagnostic probe of high density (saturation) physics. We show that by introducing and varying a transverse momentum cutoff in the definition of the average transverse momentum, one can eliminate the uncertainty in the overall magnitude of the leading order hadron production cross section in high energy collisions, and semi-quantitatively map the different dynamical regions predicted by the saturation physics. We discuss the applications of this method to pion production at RHIC and LHC and make quantitative predictions for the average transverse momentum of produced pions in the kinematics appropriate for the RHIC and LHC experiments.