Energy dependence of pi-zero production in Cu+Cu collisions at sqrt(s_NN) = 22.4, 62.4, and 200 GeV

TL;DR

This study measures neutral pion spectra in Cu+Cu collisions at three energies, revealing suppression at higher energies due to parton energy loss and enhancement at lower energy due to initial state effects.

Contribution

It provides the first detailed comparison of pi-zero production across multiple energies in Cu+Cu collisions, highlighting the energy dependence of nuclear modification effects.

Findings

Suppression of pi-zero yields at 62.4 and 200 GeV in central collisions.

Enhancement of pi-zero yields at 22.4 GeV in central collisions.

Final state energy loss dominates at higher energies, initial state effects at lower energy.

Abstract

Neutral pion transverse momentum (pT) spectra at mid-rapidity (|y| < 0.35) were measured in Cu+Cu collisions at \sqrt s_NN = 22.4, 62.4, and 200 GeV. Relative to pi -zero yields in p+p collisions scaled by the number of inelastic nucleon-nucleon collisions (Ncoll) at the respective energies, the pi-zero yields for pT \ge 2 GeV/c in central Cu+Cu collisions at 62.4 and 200 GeV are suppressed, whereas an enhancement is observed at 22.4 GeV. A comparison with a jet quenching model suggests that final state parton energy loss dominates in central Cu+Cu collisions at 62.4 GeV and 200 GeV, while the enhancement at 22.4 GeV is consistent with nuclear modifications in the initial state alone.