Charm Production at RHIC

Abstract

Observations by the PHENIX and STAR collaborations suggest that a strongly coupled quark-gluon plasma is produced in heavy-ion collisions at the Relativistic Heavy Ion Collider (RHIC). After a brief introduction to heavy-ion physics, measurements of heavy-quark production in heavy-ion collisions and the modification of heavy-quark spectra by the QGP are presented. Measurements of the total charm cross-section in several different collision systems confirm that charm quark-antiquark pairs are produced through parton hard-scattering in the initial stages of the collisions. Non-photonic electrons (proxies for heavy quarks) are suppressed by about a factor of 5 in central Au + Au collisions relative to p + p collisions. This is larger than most current theoretical predictions and has lead to a re-examination of heavy-quark energy loss in the medium. The relative contributions of c and b decays to the non-photonic electron spectrum have been predicted by perturbative QCD calculations; STAR measurements of azimuthal correlation functions of non-photonic electrons and hadrons agree with these predictions.