Inclusive Two-Gluon and Valence Quark-Gluon Production in DIS and pA

TL;DR

This paper develops a Color Glass Condensate-based calculation of inclusive two-particle production in high-energy DIS and proton-nucleus collisions. It starts from the McLerran-Venugopalan quasi-classical framework to derive a detailed two-gluon cross section and a valence quark-gluon cross section, both expressed in terms of dipole and quadrupole Wilson-line S-matrices. It then incorporates nonlinear small-x evolution via BK/JIMWLK equations, uncovering an explicit violation of AGK cutting rules in the two-gluon channel and identifying the leading-twist limit where standard $k_T$-factorization is recovered. The results provide a rigorous basis for predicting two-particle azimuthal correlations and forward-rapidity phenomena at RHIC and LHC, and they connect DIS and $pA$ observables within a unified CGC framework.

Abstract

We calculate production cross sections of a forward quark-gluon pair and of two gluons at mid-rapidity in Deep Inelastic Scattering and in high energy proton-nucleus collisions. The calculation is performed in the framework of the Color Glass Condensate formalism. We first calculate the cross sections in the quasi-classical approximation, which includes multiple rescatterings in the target. We then proceed to include the effects of non-linear small-x evolution in the production cross sections. It is interesting to note that our result for the two-gluon production cross section appears to be in direct violation of AGK cutting rules, which is the first example of such violation in QCD. The calculated quark-gluon and gluon-gluon production cross sections can be used to construct theoretical predictions for two-particle azimuthal correlations at RHIC and LHC (I^{p(d)A}) as well as for Deep Inelastic Scattering experiments at HERA and eRHIC.

Figures (14)

• Figure 1: Two-gluon production in DIS on a nucleus including multiple rescatterings.
• Figure 2: Possible orderings of the emission of the two gluons by the quark-antiquark pair.
• Figure 3: All possible emission of the harder gluon $\# 2$ by the $q\bar{q}$ pair.
• Figure 4: All possible emissions of the softer gluon $\# 1$ by the "dipole" $2,2',{\tilde{0}}$.
• Figure 5: Feynman diagram corresponding to single gluon production cross section given by Eq. (\ref{['1Gincl']}). Emitted gluon is denoted by the cross.