Neutral pion production in Au+Au collisions at RHIC

TL;DR

This paper reports on the suppression of neutral pion production in Au+Au collisions at RHIC energies, highlighting the role of initial state effects and the azimuthal dependence of suppression patterns, with implications for theoretical models.

Contribution

It provides new experimental data on neutral pion suppression at multiple energies and analyzes the azimuthal dependence to distinguish between theoretical models.

Findings

Suppression of neutral pions observed at 39 and 62.4 GeV.

High pT suppression patterns are similar at 62.4 and 200 GeV.

Data favors the ASW model with AdS/CFT over pQCD-based models.

Abstract

New results from the 2010 RHIC low energy program show a substantial suppression of neutral pions in central Au+Au collisions at both sqrt{s_NN}=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 R_AA is strongly correlated with the (approximately elliptical) geometry of the overlap region. The dependence of R_AA on the reaction plane, determined up to pT=20 GeV/c from 2007 high-luminosity sqrt{s_NN}=200 GeV Au+Au data provides great selectivity among theories, and favours the ASW scenario with AdS/CFT correspondence over the pQCD-based models.