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

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 $\frac{1}{Q^2}$ and $\frac{1}{N_c^2}$ 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 $\frac{1}{N_c}$ so they appear to be relatively small in accordance with LHC results.

Comments: 80 pages and 5 figures, typos corrected, references added. arXiv admin note: text overlap with arXiv:2012.01588