Azimuthal anisotropy of neutral pion production in Au+Au collisions at sqrt(sNN) = 200 GeV: Path-length dependence of jet quenching and the role of initial geometry
Abstract
We have measured the azimuthal anisotropy of pi0's for 1 < pT < 18 GeV/c for Au+Au collisions at sqrt sNN = 200 GeV. The observed anisotropy shows a gradual decrease in 3 < pT < 7 - 10 GeV/c, but remains positive beyond 10 GeV/c. The magnitude of this anisotropy is under-predicted, up to at least 10 GeV/c, by current perturbative QCD (pQCD) energy-loss model calculations. An estimate of the increase in anisotropy expected from initial-geometry modification due to gluon saturation effects and initial-geometry fluctuations is insufficient to account for this discrepancy. Calculations which implement a path length dependence steeper than what is implied by current pQCD energy-loss models, show reasonable agreement with the data.
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