Event-by-event azimuthal anisotropy of jet quenching in relativistic   heavy ion collisions
  In this paper we present with full details a systematic quantification, on an even-by-event basis, of the hard probe response to the geometry and fluctuations of the hot QCD matter created in heavy ion collisions at both the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC). The azimuthal anisotropy of jet quenching is extracted and decomposed as harmonic responses (for n=1,2,3,4,5,6) to the corresponding harmonics in the fluctuating initial condition. We show that such jet response harmonics are sensitive to the jet quenching models as well as to the bulk matter initial compositions. By studying these for all centralities at both RHIC and LHC energies we put a strong constraint on the path-length and medium-density dependence of jet energy loss. We also examine the hard-soft di-hadron correlation arising from the hard and soft sectors' responses to the common initial fluctuations. We demonstrate that the experimentally observed "hard-ridge" can be explained this way and that its dependence on the trigger-azimuthal-angle could also be qualitatively understood. 
Xilin Zhang and Jinfeng Liao
nucl-th hep-ph nucl-ex