Dilepton production from the Color Glass Condensate

TL;DR

The paper addresses dilepton production in high-energy proton-nucleus and forward nucleus-nucleus collisions as a probe of Color Glass Condensate and gluon saturation. It extends prior real-photon work to virtual photons, deriving a differential cross-section for $qA \to q l^+ l^- X$ that is governed by a universal saturation correlator $C(l_\perp)$ tied to the nuclear saturation scale $Q_s(x)$. A key result is the inclusive cross-section, which exhibits a transition in transverse momentum behavior from $1/l_\perp^4$ to $1/l_\perp^2$ around $Q_s$, with forward rapidity enhancing saturation effects. The framework enables connections to $pA$ and $AA$ phenomenology via convolution with parton distribution functions and can guide experimental tests of CGC physics at RHIC/LHC, including potential extraction of shadowing and saturation signatures.

Abstract

We consider dilepton production in high energy proton-nucleus (and very forward nucleus-nucleus) collisions. Treating the target nucleus as a Color Glass Condensate and describing the projectile proton (nucleus) as a collection of quarks and gluons as in the parton model, we calculate the differential cross section for dilepton production in quark-nucleus scattering and show that it is very sensitive to the saturation scale characterizing the target nucleus.

Figures (1)

• Figure 1: A typical contribution to the cross-section for lepton pair production in pA collisions. The black dot denotes the re-summed interactions of the incoming quark with the classical color field of the nucleus. This is the square of the term where the photon is emitted after the scattering on the nucleus. There is also a term where the photon is emitted first, and interferences thereof, not represented here.