Azimuthal anisotropy: Ridges, recombination, and breaking of quark number scaling

Abstract

Azimuthal anisotropy is studied by taking into account the ridges created by semihard scattering, which is sensitive to the initial spatial configuration in noncentral heavy-ion collisions. No rapid thermalization is required. Although hydrodynamics is not used in this study, the validity of hydrodynamical expansion is not excluded at later time after equilibration is achieved. Phenomenological properties of the bulk and ridge behaviors are used as inputs to determine the elliptic flow of pion and proton at low p{sub T}. At intermediate p{sub T} the recombination of shower partons with thermal partons becomes more important. The {phi} dependence arises from the variation of the in-medium path length of the hard parton that generates the shower. The p{sub T} dependence of v{sub 2} is therefore very different at intermediate p{sub T} compared to that at low p{sub T}. Quark number scaling of v{sub 2} is shown to be only approximately valid at low p{sub T}, but is broken at intermediate p{sub T}, even though recombination is the mechanism of hadronization in all p{sub T} regions considered.