Neutral pion production with respect to centrality and reaction plane in Au+Au collisions at √sNN=200 GeV

Adare, A. and Afanasiev, S. and Aidala, C. and Ajitanand, N. N. and Akiba, Y. and Al-Bataineh, H. and Alexander, J. and Aoki, K. and Aramaki, Y. and Atomssa, E. T. and Averbeck, R. and Awes, T. C. and Azmoun, B. and Babintsev, V. and Bai, M. and Baksay, G. and Baksay, L. and Barish, K. N. and Bassalleck, B. and Basye, A. T. and Bathe, S. and Baublis, V. and Baumann, C. and Bazilevsky, A. and Belikov, S. and Belmont, R. and Bennett, R. and Berdnikov, A. and Berdnikov, Y. and Bickley, A. A. and Csanád, Máté and Csörgő, Tamás and Dávid, Gábor and Kiss, Ádám and Nagy, Márton and Sziklai, János István and Tarján, Péter and Vértesi, Róbert (2013) Neutral pion production with respect to centrality and reaction plane in Au+Au collisions at √sNN=200 GeV. PHYSICAL REVIEW C, 87 (3). ISSN 2469-9985

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Abstract

The PHENIX experiment has measured the production of π0s in Au+Au collisions at √sN N = 200 GeV. The new data offer a fourfold increase in recorded luminosity, providing higher precision and a larger reach in transverse momentum, pT , to 20 GeV/c. The production ratio of η/π0 is 0.46±0.01(stat)±0.05(syst), constant with pT and collision centrality. The observed ratio is consis- tent with earlier measurements, as well as with the p+p and d+Au values. π0 are suppressed by a factor of 5, as in earlier findings. However, with the improved statistical precision a small but significant rise of the nuclear modification factor RAA vs pT , with a slope of 0.0106±0.0034 0.0029 [Gev/c]−1 , is discernible in central collisions. A phenomenological extraction of the average fractional parton energy loss shows a decrease with increasing pT . To study the path length dependence of sup- pression, the π0 yield was measured at different angles with respect to the event plane; a strong azimuthal dependence of the π0 RAA is observed. The data are compared to theoretical models of parton energy loss as a function of the path length, L, in the medium. Models based on pQCD are insufficient to describe the data, while a hybrid model utilizing pQCD for the hard interactions and AdS/CFT for the soft interactions is consistent with the data.

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