Relationship between the azimuthal dependencies of nuclear modification factor and ridge yield

The azimuthal angular dependence of the nuclear modification factor RAA(pT,φ,Npart) recently obtained by PHENIX is related at low pT to the trigger φ dependence of the ridge yield as measured by STAR in a framework in which the azimuthal anisotropy is driven by semihard scattering near the surface. Careful consideration of the initial geometry leads to the determination of a surface segment in which the production of semihard partons are responsible for the φ dependence of the inclusive distribution on the one hand and for the angular correlation in ridge phenomenology on the other. With v2 also being well reproduced along with RAA and ridge yield, all relevant φ dependencies in heavy-ion collisions can now be understood in a unified description that emphasizes the ridge production whether or not a trigger is used.