The origin of large- p T p 0 suppression at RHIC

Abstract We present results for inclusive π0 production in proton–proton and in Au–Au at RHIC energy s =200 GeV. We use next-to-leading order perturbative QCD calculation and we include nuclear effects such as parton energy loss and nuclear shadowing. We consider the ratio of π0 distribution in Au–Au and p–p collisions for pT>3 GeV for three cases of parton energy loss: (1) constant parton energy loss per parton scattering, ϵan=const, (2) Landau–Pomeranchuk–Migdal energy-dependent energy loss, ϵ a n ∼ E a n and (3) Bethe–Heitler energy-dependent energy loss, ϵan∼Ean. We show that recently observed suppression of π0 production in Au–Au collisions at RHIC, which is found to increase with pT increasing from 3 GeV to 8 GeV, can be reproduced by ϵan=0.06Ean. We show that the ratio of prompt photons to neutral pions produced in Au–Au collisions at RHIC has a strong pT dependence approaching one at pT∼ 10 GeV.