Nuclear dependence coefficientα(A,qT)for Drell-Yan andJ/ψproduction

Abstract

Define the nuclear dependence coefficient $\ensuremath{\alpha}{(A,q}_{T})$ in terms of the ratio of the transverse momentum spectrum in hadron-nucleus and in hadron-nucleon collisions $d{\ensuremath{\sigma}}^{\mathrm{hA}}{/dq}_{T}^{2}/d{\ensuremath{\sigma}}^{\mathrm{hN}}{/dq}_{T}^{2}\ensuremath{\equiv}{A}^{\ensuremath{\alpha}{(A,q}_{T})}.$ We argue that, in the small ${q}_{T}$ region, the $\ensuremath{\alpha}{(A,q}_{T})$ for the Drell-Yan and $J/\ensuremath{\psi}$ production is given by a universal function ${a+bq}_{T}^{2},$ where the parameters a and b are completely determined by either calculable quantities or independently measurable physical observables. We demonstrate that this universal function $\ensuremath{\alpha}{(A,q}_{T})$ is insensitive to A for normal nuclear targets. For a color deconfined nuclear medium, $\ensuremath{\alpha}{(A,q}_{T})$ becomes strongly dependent on A. We also show that our $\ensuremath{\alpha}{(A,q}_{T})$ for the Drell-Yan process is naturally linked to the perturbatively calculated $\ensuremath{\alpha}{(A,q}_{T})$ at large ${q}_{T}$ without any free parameters, and $\ensuremath{\alpha}{(A,q}_{T})$ is consistent with E772 data for all ${q}_{T}.$