Nuclear dependence coefficient $\alpha(A,q_T)$ for the Drell-Yan and J/$\psi$ production

TL;DR

This paper introduces a universal model for the nuclear dependence coefficient in Drell-Yan and J/ψ production, showing its insensitivity to nuclear size in normal nuclei and its A-dependence in deconfined media, consistent with experimental data.

Contribution

It proposes a universal, parameter-free function for the nuclear dependence coefficient in small transverse momentum regions, linking it to measurable quantities and perturbative calculations.

Findings

Universal function $\alpha(A,q_T)$ fits data for normal nuclei.

$\alpha(A,q_T)$ depends on nuclear medium state.

Model aligns with E772 experimental results.

Abstract

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