The azimuthal angular dependence of the nuclear modification factor $R_{\mathit{AA}}(p_T,\varphi ,N_{\mathrm{part}})$ recently obtained by PHENIX is related at low $p_T$ to the trigger $\varphi$ 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 $\varphi$ dependence of the inclusive distribution on the one hand and for the angular correlation in ridge phenomenology on the other. With $v_2$ also being well reproduced along with $R_{\mathit{AA}}$ and ridge yield, all relevant $\varphi$ 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.

• Received 8 September 2009

DOI:https://doi.org/10.1103/PhysRevC.81.034904