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Non-Universality of Transverse Momentum Dependent Parton Distributions at Small-x

Bo-Wen Xiao, Feng Yuan

TL;DR

Addresses whether small-x transverse momentum dependent parton distributions are universal across processes. The authors build and solve an explicit Abelian scalar QED model to sum initial/final state interactions to all orders and compare pA dijet production with DIS. They find a process-dependent phase arising from these interactions that breaks universality at leading power, whereas integrated distributions remain universal; they discuss implications for interpreting di-hadron correlations in dA collisions and propose future work within saturation frameworks.

Abstract

We study the universality issue of the transverse momentum dependent parton distributions at small-x, by comparing the initial/final state interaction effects in dijet-correlation in pA collisions with those in deep inelastic lepton nucleus scattering. We demonstrate the non-universality by performing an explicit calculation in a particular model where the multiple gauge boson exchange contributions are summed up to all orders. We comment on the implications of our results on the theoretical interpretation of di-hadron correlation in dA collisions in terms of the saturation phenomena in deep inelastic lepton nucleus scattering.

Non-Universality of Transverse Momentum Dependent Parton Distributions at Small-x

TL;DR

Addresses whether small-x transverse momentum dependent parton distributions are universal across processes. The authors build and solve an explicit Abelian scalar QED model to sum initial/final state interactions to all orders and compare pA dijet production with DIS. They find a process-dependent phase arising from these interactions that breaks universality at leading power, whereas integrated distributions remain universal; they discuss implications for interpreting di-hadron correlations in dA collisions and propose future work within saturation frameworks.

Abstract

We study the universality issue of the transverse momentum dependent parton distributions at small-x, by comparing the initial/final state interaction effects in dijet-correlation in pA collisions with those in deep inelastic lepton nucleus scattering. We demonstrate the non-universality by performing an explicit calculation in a particular model where the multiple gauge boson exchange contributions are summed up to all orders. We comment on the implications of our results on the theoretical interpretation of di-hadron correlation in dA collisions in terms of the saturation phenomena in deep inelastic lepton nucleus scattering.

Paper Structure

This paper contains 3 sections, 8 equations, 3 figures.

Table of Contents

  1. Introduction
  2. Initial and Final State Interaction Effects
  3. Summary and Discussions

Figures (3)

  • Figure 1: (a) Schematic diagram showing that two partons from the nucleon projectile and the nucleus target collide and produce two jets in the final state, where the intrinsic transverse momentum $q_\perp$ from nucleus dominates the imbalance between the two jets; (b) illustration of initial/final state interactions which may affect the transverse momentum dependent quark distribution from the nucleus in this process; (c) as a comparison, only the final state interaction effect is present in the deep inelastic lepton-nucleus (nucleon) scattering.
  • Figure 2: Lowest-order graphs for di-jet production in hadron-hadron collision at small-x limit. In these graphs, there is one soft gluon exchange with momentum $k$ in addition to the hard gluon exchange.
  • Figure 3: Example diagrams for two (a) and three (b) gluons exchanges, where the gluons can attach all charge particles in the upper part of the diagrams from the nucleus target.