The Nuclear Suppression Factor for PT increasing towards the Kinematic Limit
Abstract
The suppression of high transverse momentum PT hadron production in ultrarelativistic heavy-ion (A-A) collisions as compared to the scaled expectation from proton-proton (p-p) collisions expressed as the nuclear modification factor RAA is experimentally well established and can be traced back to interactions between the hard parton shower and the soft bulk matter. Physical intuition suggests that the medium modification should cease to be important when the hard scale of parton production is much larger than the typical momentum scale in the medium (e.g. the temperature T) and that consequently RAA(PT) -> 1 for PT >> T. However, RAA is not a 'simple' observable, but rather results from many different mechanisms which influence what happens when PT increases. In particular, RAA does not necessarily approch unity even if the hadron momentum is probed at the kinematic limit of the reaction. The aim of this work is to identify and discuss such mechanisms and to present different model expectations of what one would find if one could measure suppression out to the kinematic limit for hard hadron production and give predictions for the PT dependence at both RHIC and LHC.