Study of Jet Quench via Azimuthal Anisotropies with PID

Large azimuthal anisotropies $v_2$ are also one of the exciting discoveries from RHIC. Compared with collisions at lower energies, $v_2$ observed at RHIC is found to be larger, which suggests quicker thermalization; much quicker than what is expected from ordinal hadronic rescatterings. Thus the large $v_2$ implies other ingredients for thermalization than hadrons. As shown in Fig.4, dependence on transverse momentum provides important clue to understand the mechanism. At lower $p_T$ region, split of pion/kaon/proton which is consistent with hydrodynalical flow picture, has been seen while at higher $p_T$ clear departure from the hydrodynamic behaviour has been observed. Above 2 GeV/c, the way it depart from the hydrodynamic behaviour is considered to depend on the jet quench effects and/or gluon densities. Extension of PID capability will enable us to study these phenomena at higher $p_T$ region where observables might have more sensitivities on jet physics.

図 4: Azimuthal anisotropies in Au+Au at $\sqrt {s_{NN}}$ = 200 GeV with PID [left] for negative, and [middle] for positive [shown at QM2002, (PHENIX)] and [right] theoretical predictions based on jet quench scenario [M. Gyulassy et al.,Phys.Lett.B526(2002)301.].