Abstract
We have measured the azimuthal anisotropy of production for for collisions at . The observed anisotropy shows a gradual decrease for , but remains positive beyond . The magnitude of this anisotropy is underpredicted, up to at least , 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 fluctuations is insufficient to account for this discrepancy. Calculations that implement a path-length dependence steeper than what is implied by current PQCD energy-loss models show reasonable agreement with the data.
- Received 18 June 2010
DOI:https://doi.org/10.1103/PhysRevLett.105.142301
© 2010 The American Physical Society