Gauge-invariant TMD factorization for Drell-Yan hadronic tensor at small x

Abstract

Abstract The Drell-Yan hadronic tensor for electromagnetic (EM) current is calculated in the Sudakov region $$ s\gg {Q}^2\gg {q}_{\perp}^2 $$ s ≫ Q 2 ≫ q ⊥ 2 with $$ \frac{1}{Q^2} $$ 1 Q 2 accuracy, first at the tree level and then with the double-log accuracy. It is demonstrated that in the leading order in Nc the higher-twist quark-quark-gluon TMDs reduce to leading-twist TMDs due to QCD equation of motion. The resulting tensor for unpolarized hadrons is EM gauge-invariant and depends on two leading-twist TMDs: f1 responsible for total DY cross section, and Boer-Mulders function $$ {h}_1^{\perp } $$ h 1 ⊥ . The order-of-magnitude estimates of angular distributions for DY process seem to agree with LHC results at corresponding kinematics.