Drell-Yan Angular Lepton Distributions at Small <i>x</i> from TMD Factorization
Ian Balitsky
Abstract
The Drell-Yan process is studied in the framework of TMD factorization in the Sudakov region s » Q2 » q2⊥ corresponding to recent LHC experiments with Q2 of order of mass of Z-boson and transverse momentum of DY pair ∼ few tens GeV. The DY hadronic tensors are expressed in terms of quark and quark-gluon TMDs with 1Q2 and 1Nc2 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 hadronic tensors depend on two leading-twist TMDs: f1 responsible for total DY cross section, and Boer-Mulders function h⊥1. The corresponding qualitative and semi-quantitative predictions seem to agree with LHC data on five angular coefficients A0 − A4 of DY pair production. The remaining three coefficients A5 − A7 are determined by quark-quark-gluon TMDs multiplied by extra 1Nc so they appear to be relatively small in accordance with LHC results.