Probing small-$x$ gluons by low-mass Drell-Yan pairs at colliders

Abstract

The transverse-momentum ($Q_T$) distribution of low-mass Drell-Yan pairs is calculated in QCD perturbation theory with all-order resummation of ${\alpha }_s({\alpha }_s\ln (Q_T^2/Q^2){)}^n$ type terms. We demonstrate that the rapidity distribution of low-mass Drell-Yan pairs at large-enough transverse momentum is an advantageous source of constraints on the gluon distribution and its nuclear dependence. We argue that low-mass Drell-Yan pairs in the forward region provide a good and clean probe of small-$x$ gluons at collider energies.

25 pages, 16 figures