Single-spin asymmetry ATsin(2ϕ−ϕS) in π−p Drell-Yan process within TMD factorization

We study the single-spin asymmetry ATsin(2ϕ−ϕS) in the pion-induced Drell-Yan process within the transverse momentum dependent factorization (TMD factorization). The asymmetry can be expressed as the convolution of the Boer-Mulders function and the transversity function. We numerically estimate the asymmetry ATsin(2ϕ−ϕS) at the COMPASS kinematics with the model results for the pion meson distributions from the light-cone wave function approach and the available parametrization for the proton distributions. We also include the TMD evolution formalism both proton and pion parton distribution functions by using two different parametrizations on nonperturbative Sudakov form factor. We find that the asymmetry ATsin(2ϕ−ϕS) as functions of xp, xπ, xF and q⊥ is qualitatively consistent with the recent COMPASS measurement.

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

The Drell-Yan process is studied in the framework of TMD factorization in the Sudakov region s » Q2 » $$ {q}_{\perp}^2 $$ q ⊥ 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 $$ \frac{1}{Q^2} $$ 1 Q 2 and $$ \frac{1}{N_c^2} $$ 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 $$ {h}_1^{\perp } $$ 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 $$ \frac{1}{N_c} $$ 1 N c so they appear to be relatively small in accordance with LHC results.

Transverse momentum-dependent parton distributions of pion in the light-front holographic model

Using the light-front holographic model, we study the transverse momentum-dependent parton distributions (TMDs) for the case of pion. At leading twist, the unpolarized parton distribution function [Formula: see text] and the Boer–Mulders function [Formula: see text] are obtained for pion. We calculate both the functions using the light-front holographic model with spin improved wave function and compare the predicted results with available results of other models. In order to provide inputs in predicting future experimental data, an LO evolution is performed from model scale to experimental scale for the case of unpolarized parton distribution function [Formula: see text].

How to measure the linear polarization of gluons in unpolarized proton using the heavy-quark pair production

In recent papers [1, 2], two new ways have been proposed to probe the linear polarization of gluons in unpolarized proton: using the azimuthal asymmetries and Callan-Gross ratio in heavy-quark pair leptoproduction, lN → l′QQ̅X. In this talk, we discuss in details the sensitivity of the QCD predictions for the azimuthal cos φ and cos 2φ asymmetries to the contribution of linearly polarized gluons inside unpolarized proton, where the azimuth φ is the angle between the lepton scattering plane (l, l′) and the heavy quark production plane (N, Q). Our analysis shows that the azimuthal distributions under consideration vary from 0 to 1 depending on the value of the gluonic counterpart of the Boer- Mulders function, $h_{1}^{ \bot g}$. We conclude that the cos φ and cos 2φ asymmetries in heavy-quark pair production in DIS processes are predicted to be large in wide kinematic ranges and sensitive to the contribution of linearly polarized gluons.

Measurement of Boer-Mulders Function via Drell-Yan Process by SeaQuest Experiment at Fermilab

The SeaQuest experiment is being carried out at Fermi National Accelerator Lab (FNAL) to investigate the nucleon structure with the Drell-Yan process. It utilizes the 120-GeV proton beam extracted from the FNAL Main Injector and targets of liquid hydrogen, liquid deuterium, carbon, iron and tungsten. The solid targets are used to measure the nuclear effects. This paper describes the flavor asymmetry of light anti-quark distributions in the proton ([Formula: see text]) and the angular distribution of Drell-Yan process. The Boer-Mulders function ([Formula: see text]) can be derived from the size ([Formula: see text]) of [Formula: see text] modulation. SeaQuest finished the second data-taking period in August 2014. Preliminary results of [Formula: see text] and [Formula: see text] are reported.