Neutral pion production in Au + Au collisions at RHIC

New results from the 2010 RHIC low energy program show a substantial suppression of neutral pions in central Au + Au collisions at both sNN=39 and 62.4 GeV c.m.s. energies. At high pT the 62.4 GeV and 200 GeV data follow the same suppression pattern. On the other hand, otherwise successful pQCD predictions do not describe the 39 GeV data. These observations indicate that initial state effects may play a dominant role at smaller c.m.s. energies and at lower pT. The azimuthal dependence of the nuclear modification factor RAA is strongly correlated with the (approximately elliptical) geometry of the overlap region. The dependence of RAA on the reaction plane, determined up to pT=20GeV/c from 2007 high-luminosity sNN=200GeV Au + Au data provides great selectivity among theories, and favours the ASW scenario with AdS/CFT correspondence over the pQCD-based models.