From DIS to proton-nucleus collisions in the Color Glass Condensate model

TL;DR

The work identifies a universal quark antiquark dipole cross section, encapsulated by Wilson line correlators in the Color Glass Condensate, as the key building block linking Deep Inelastic Scattering and proton-nucleus collisions. By reformulating DIS and forward pA processes in terms of this dipole cross section, the authors preserve universality beyond leading twist and enable DIS data to constrain pA predictions. They compare several dipole models, including the McLerran-Venugopalan, GBW, and BGK schemes, and show that the MV model yields a Cronin-type enhancement at intermediate transverse momentum while suppressing low-pT production, with the crossover depending on rapidity. The framework provides a path to predict hadron, jet, photon, and dilepton production in pA collisions and to use forward data to refine or rule out dipole cross-section models.

Abstract

We show that particle production in proton-nucleus (pA) collisions in the Color Glass Condensate model can be related to Deep Inelastic Scattering of leptons on protons/nuclei (DIS). The common building block is the quark antiquark (or gluon-gluon) dipole cross section which is present in both DIS and pA processes. This correspondence in a sense generalizes the standard leading twist approach to pA collisions based on collinear factorization and perturbative QCD, and allows one to express the pA cross sections in terms of a universal quantity (dipole cross section) which, in principle, can be measured in DIS or other processes. Therefore, using the parameterization of dipole cross section at HERA, one can calculate particle production cross sections in proton-nucleus collisions at high energies. Alternatively, one could use proton-nucleus experiments to further constrain models of the dipole cross-section. We show that the McLerran-Venugopalan model predicts enhancement of cross sections at large p_t (Cronin effect) and suppression of cross sections at low p_t. The cross over depends on rapidity and moves to higher p_t as one goes to more forward rapidities.

Figures (5)

• Figure 1: The relevant diagrams for $\gamma^*A\to q\bar{q}X$ in the Color Glass Condensate model. The black dots denote the eikonal interaction between the quark or antiquark with the classical color field.
• Figure 2: The relevant diagrams for $qA\to q\gamma^* X$ in the Color Glass Condensate model. The black dots denote the eikonal interaction between the quark or antiquark with the classical color field.
• Figure 3: The relevant diagram for $qA\to qX$ in the Color Glass Condensate model. The black dots denote the eikonal interaction between the quark or antiquark with the classical color field.
• Figure 4: Cronin effect at the partonic level in the McLerran-Venugopalan model. The reference nucleus is chosen such that the corresponding saturation scale is $Q_s^2{}_{\rm ref}=1$GeV${}^2$. This reference value of $Q_s$ is compared to nuclei for which $Q_s^2=2$ GeV${}^2$ and $Q_s^2=3$ GeV${}^2$. The infrared cutoff is set to $\Lambda=200$ MeV.
• Figure 5: Values of $-q_\perp^4 \widetilde{\sigma}_{\rm dipole}(q_\perp)$ as a function of $q_\perp$, for several values of $x$ in the model of Bartels, Golec-Biernat and Kowalski.