Quenching of photon and pion spectra at intermediate RHIC energy

TL;DR

This paper calculates prompt photon and pion spectra at intermediate RHIC energy, predicting significant pion quenching and photon suppression due to energy loss and nuclear effects, with detailed NLO p-p results.

Contribution

It provides the first NLO p-p calculations at this energy and predicts energy loss effects on photon and pion spectra in Au-Au collisions.

Findings

Pion quenching is nearly as strong as at higher energies.

Photon energy loss effects are small due to phase-space restrictions.

High-pt photon suppression is significant because of isospin and nuclear density effects.

Abstract

Single prompt photon and pion spectra in p-p and Au-Au collisions at intermediate RHIC energy, s^1/2 = 62.4 GeV, are computed at large transverse momentum in perturbative QCD. Next-to-leading order calculations in p-p scattering are first presented. The quenching of the prompt photon and pion yield due to energy loss processes in central Au-Au with respect to p-p collisions is then predicted. At this energy, the small phase-space available to produce hard partons makes the pion quenching almost as pronounced as at s^1/2 = 200 GeV, despite the smaller gluon density of the produced medium. In the photon sector, energy loss effects prove small because of this very phase-space restriction, which favours the direct production channel. A significant suppression of high-pt photons is however predicted, because of a strong isospin effect together with the depletion of nuclear parton densities at large x.