The Origin of Large-p_T pi^0 Suppression at RHIC

Abstract

We present results for inclusive ${\pi }^0$ production in proton-proton and in Au-Au at RHIC energy $\sqrt{s}=200$ 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 ${\pi }^0$ distribution in Au-Au and p-p collisions for $p_T>3$ GeV for three cases of parton energy loss: 1) constant parton energy loss per parton scattering, ${ϵ}_n^a=const$, 2) Landau-Pomeranchuk-Migdal energy-dependent energy loss, ${ϵ}_n^a\sim {\sqrt{E}}_n^a$ and 3) Bethe-Heitler energy-dependent energy loss, ${ϵ}_n^a\sim E_n^a$. We show that recently observed suppression of ${\pi }^0$ production in Au-Au collisions at RHIC, which is found to increase with $p_T$ increasing from 3GeV to 8GeV, can be reproduced by ${ϵ}_n^a=0.06E_n^a$. We show that the ratio of prompt photons to neutral pions produced in Au-Au collisions at RHIC has a strong $p_T$ dependence approaching one at $p_T\sim 10$GeV.

Comments: minor corrections; version accepted for publication in Physics Letters B