Drell-Yan angular lepton distributions at small $x$ from TMD factorization

TL;DR

This paper analyzes Drell-Yan lepton angular distributions at small x using TMD factorization, demonstrating that leading-twist TMDs suffice to describe key angular coefficients and aligning predictions with LHC data.

Contribution

It shows that higher-twist quark-gluon TMDs reduce to leading-twist TMDs at leading order in N_c, simplifying the description of Drell-Yan angular distributions.

Findings

Predictions for angular coefficients A0-A4 agree with LHC data.

Coefficients A5-A7 are small, consistent with experimental results.

Leading-twist TMDs f1 and h1^⊥ dominate the Drell-Yan process.

Abstract

The Drell-Yan process is studied in the framework of TMD factorization in the Sudakov region $s\gg Q^2\gg q_\perp^2$ corresponding to recent LHC experiments with $Q^2$ of order of mass of Z-boson and transverse momentum of DY pair $\sim$ few tens GeV. The DY hadronic tensors are expressed in terms of quark and quark-gluon TMDs with ${1\over Q^2}$ and ${1\over N_c^2}$ accuracy. It is demonstrated that in the leading order in $N_c$ the higher-twist quark-quark-gluon TMDs reduce to leading-twist TMDs due to QCD equation of motion. The resulting hadronic tensors depend on two leading-twist TMDs: $f_1$ responsible for total DY cross section, and Boer-Mulders function $h_1^\perp$. The corresponding qualitative and semi-quantitative predictions seem to agree with LHC data on five angular coefficients $A_0-A_4$ of DY pair production. The remaining three coefficients $A_5-A_7$ are determined by quark-quark-gluon TMDs multiplied by extra ${1\over N_c}$ so they appear to be relatively small in accordance with LHC results.