Quark TMDs from back-to-back dijet production at forward rapidities in pA collisions beyond eikonal accuracy in the CGC

TL;DR

This work extends the CGC-based treatment of forward pA dijet production by including NEik corrections arising from the target quark background, focusing on t-channel quark exchange contributions. Across the channels g→gq, q→q q̄, q→gg, and q→qq, the authors compute general amplitudes, their back-to-back limits, and back-to-back cross sections, revealing a universal factorized structure in which a quark TMD from the target multiplies a channel-specific hard factor. The analysis unifies the role of gauge-link content and color structures, establishing explicit relations between the calculated cross sections and quark TMDs with various gauge links in the x≈0 regime. The results set the stage for applications to pA phenomenology at forward rapidities and motivate future work on NEik corrections in pure gluon backgrounds and related observables such as photon+jet production, with potential implications for accessing quark TMDs in high-energy QCD.

Abstract

We study dijet production in pA collisions at forward rapidities at next-to-eikonal accuracy. We restrict ourselves to the next-to-eikonal corrections that are induced by the quark background field of the target. We consider all possible channels, compute scattering amplitudes both in general kinematics and in the back-to-back limit. By using these results, we compute the back-to-back production cross section and obtain a factorized expression with a quark TMD times associated hard factor for each channel.

Figures (17)

• Figure 1: Diagrams contributing to channel $g\to gq$.
• Figure 2: Color structures appearing in the cross section of $g\to gq$.
• Figure 3: Diagrams contributing to channel $q \to q\bar{q}$.
• Figure 4: Color structures appearing in the cross section of $q \to q\bar{q}$.
• Figure 5: Diagrams contributing to channel $q\to gg$.