Physics & Astronomy Faculty and Staff Publications

Document Type

Article

Publication Date

5-10-2012

Abstract

Neutral-pion, _0, spectra were measured at midrapidity (|y| < 0.35) in Au+Au collisions at psNN = 39 and 62.4GeV and compared to earlier measurements at 200GeV in the 1 < pT < 10GeV/c transverse-momentum (pT ) range. The high-pT tail is well described by a power law in all cases and the powers decrease significantly with decreasing center-of-mass energy. The change of powers is very similar to that observed in the corresponding p+p-collision spectra. The nuclear-modification factors (RAA) show significant suppression and a distinct energy dependence at moderate pT in central collisions. At high pT , RAA is similar for 62.4 and 200GeV at all centralities. Perturbative-quantum-chromodynamics calculations that describe RAA well at 200GeV, fail to describe the 39GeV data, raising the possibility that the relative importance of initial-state effects and soft processes increases at lower energies. A conclusion that the region where hard processes are dominant is reached only at higher pT , is also supported by the xT dependence of the xT -scaling power-law exponent.

Language (ISO)

English

Sponsorship

http://arxiv.org/pdf/1204.1526v1.pdf

Comments

Preprint

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