Jet quenching and azimuthal anisotropy of large pT spectra in noncentral high-energy heavy-ion collisions

Parton energy loss inside a dense medium leads to the suppression of large p_T hadrons and can also cause azimuthal anisotropy of hadron spectra at large transverse momentum in noncentral high-energy heavy-ion collisions. Such azimuthal anisotropy is studied qualitatively in a parton model for heavy-ion collisions at RHIC energies. The coefficient v₂(p_T) of the elliptic anisotropy at large p_T is found to be very sensitive to parton energy loss. It decreases slowly with p_T contrary to its low p_T behavior where v₂ increases very rapidly with p_T. The turning point signals the onset of contributions of hard processes and the magnitude of parton energy loss. The centrality dependence of v₂(p_T) is shown to be sensitive to both size and density dependence of the parton energy loss and the latter can also be studied via variation of the colliding energy. The anisotropy coefficient v₂/ɛ normalized by the spatial ellipticity ɛ is found to decrease significantly toward semiperipheral collisions, differing from the hydrodynamic results for low p_T hadrons. Constrained by the existing WA98 experimental data at the SPS energy on parton energy loss, both hadron spectra suppression and azimuthal anisotropy at high p_T are predicted to vanish for b>7-8 fm in Au+Au collisions at s=130-200 GeV when the hadron rapidity density per unit area of the initial overlapped region is less than what is achieved in the central Pb+Pb collisions at the SPS energy.