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

Ian Balitsky

doi:10.1007/jhep09(2021)022

Abstract

The Drell-Yan process is studied in the framework of TMD factorization in the Sudakov region s » Q2 » {q}_{perp}^2 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 frac{1}{Q^2} and frac{1}{N_c^2} 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^{perp } . 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 frac{1}{N_c} so they appear to be relatively small in accordance with LHC results.

Highlights

The Drell-Yan (DY) process [1] has been extensively studied in high energy physics field for precise tests of QCD, investigation of the structure of the proton, and searches for possible new physics
The important part of these studies is the transverse-momentum dependence of angular distribution of DY lepton pairs with l arge invariant mass produced in hadronic collisions
The DY process at transverse momentum of lepton pair much smaller than their invariant mass, the collinear factorization should be replaced by TMD factorization [9,10,11,12,13]

Summary

Introduction

The Drell-Yan (DY) process [1] has been extensively studied in high energy physics field for precise tests of QCD, investigation of the structure of the proton, and searches for possible new physics. The important part of these studies is the transverse-momentum dependence of angular distribution of DY lepton pairs with l arge invariant mass produced in hadronic collisions. It was extensively studied in the framework of collinear factorization [2,3,4,5,6,7] leading to good agreement with experiment [8]. In this paper the DY process will be studied in so-called Sudakov plus small-x region s Q2 q⊥2 where Q2 is the invariant mass of DY pair and q⊥ is the transverse momentum of produced leptons.

Objectives

Results

Conclusion