Pictures of Particle Production in Proton-Nucleus Collisions

TL;DR

This paper investigates gluon production in proton-nucleus collisions, demonstrating how different theoretical pictures converge and deriving gluon production formulas that exhibit $k_ot$-factorization within the McLerran-Venugopalan model.

Contribution

It provides a derivation of gluon production showing $k_ot$-factorization explicitly in the MV model, linking different conceptual pictures of gluon liberation.

Findings

Derivation of gluon production in the MV model

Explicit demonstration of $k_ot$-factorization

Agreement with standard gluon density approaches

Abstract

This work focuses on gluon(jet) production in dilute(proton)-dense(nucleus) collisions. Depending on the frame and gauge, gluon production can be viewed as a freeing of gluons coming from either the proton wave function or from the nucleus wave function. These (apparently) very different pictures must lead to the same result and the purpose of this paper is to see how that happens. The focus is on gluons having $k_\perp\sim Q_S$ or gluons in the scaling region $k_\perp/Q_S\gg 1$. In the McLerran-Venugopalan(MV) model with $k_\perp\sim Q_S$ we are able to derive gluon production in a way that (graphically) manifestly shows $k_\perp$-factorization in terms of the number density of gluons in the nuclear wave function. We presume that this picture, and $k_\perp$-factorization, continues to hold in the presence of small-$x$ evolution although we have not been able to explicitly verify this. Our result is in agreement with usual $k_\perp$-factorization where the gluon number density of the nucleus does not appear in an explicit way.