Physical Review Letters
Neutral pion transverse momentum (pT) spectra at midrapidity (jyj & 0:35) were measured in Cu þ Cu collisions at ffiffiffiffiffiffiffiffi sNN p ¼ 22:4, 62.4, and 200 GeV. Relative to 0 yields in p þ p collisions scaled by the number of inelastic nucleon-nucleon collisions (Ncoll) the 0 yields for pT * 2 GeV=c in central Cu þ Cu collisions are suppressed at 62.4 and 200 GeV 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 þ Cu collisions at 62.4 and 200 GeV, while the enhancement at 22.4 GeV is consistent with nuclear modifications in the initial state alone.
Adare, A., Afanasiev, S., Aidala, C., Ajitanand, N. N., Akiba, Y., Al-Bataineh, H., . . . Zolin, L. (2008). Onset of π0 suppression studied in Cu+Cu collisions at sNN=22.4, 62.4, and 200 GeV. Physical Review Letters, 101(16)