Neutral Pion Production in Au+Au Collisions at $\sqrt{s_{NN}}$ = 200 GeV

TL;DR

This paper reports measurements of neutral pion production in gold-gold collisions at 200 GeV, showing significant suppression at high transverse momentum indicative of parton energy loss in the quark-gluon plasma.

Contribution

First detailed measurement of neutral pion spectra over a wide pT range in Au+Au collisions at RHIC, with comparison to charged pions and analysis of nuclear modification factors.

Findings

High pT neutral pion yield is suppressed by a factor of about 5 in central collisions.

Suppression pattern consistent with parton energy loss in dense medium.

Results align with previous observations for light quark mesons.

Abstract

The results of mid-rapidity ($0 < y < 0.8$) neutral pion spectra over an extended transverse momentum range ($1 < p_T < 12$ GeV/$c$) in $\sqrt{s_{NN}}$ = 200 GeV Au+Au collisions, measured by the STAR experiment, are presented. The neutral pions are reconstructed from photons measured either by the STAR Barrel Electro-Magnetic Calorimeter (BEMC) or by the Time Projection Chamber (TPC) via tracking of conversion electron-positron pairs. Our measurements are compared to previously published $\pi^{\pm}$ and $\pi^0$ results. The nuclear modification factors $R_{\mathrm{CP}}$ and $R_{\mathrm{AA}}$ of $\pi^0$ are also presented as a function of $p_T$ . In the most central Au+Au collisions, the binary collision scaled $\pi^0$ yield at high $p_T$ is suppressed by a factor of about 5 compared to the expectation from the yield of p+p collisions. Such a large suppression is in agreement with previous observations for light quark mesons and is consistent with the scenario that partons suffer considerable energy loss in the dense medium formed in central nucleus-nucleus collisions at RHIC.