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

Hui Li,Zhun Lu,Xiaoyu Wang

doi:10.1051/epjconf/202225803002

Abstract

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.

Highlights

The T-odd Boer-Mulders function h⊥1 represents the transversely polarization asymmetry of quarks inside an unpolarized hadron, which manifests the novel structure of hadrons
We adopt the model result for the distribution of the pion meson from the light-cone wave function approach, and we choose the available parametrization for the transversity distribution of the proton
As the nonperturbative part associated with the pion Boer-Mulders function is still unknown, we assume that it has the same form as that the unpolarized distribution function

Summary

Introduction

The T-odd Boer-Mulders function h⊥1 represents the transversely polarization asymmetry of quarks inside an unpolarized hadron, which manifests the novel structure of hadrons. A chiral-odd Boer-Mulders function convoluted with the transversity distribution h1 can be used to describe the asymmetry AsTin(2φ−φS ) with φS the azimuthal angle of target transverse spin. The first measurement on the sin(2φ − φS ) asymmetry has been performed by the COMPASS [1], which adopted a pion beam to collide on the transversely polarized nucleon target. We numerically estimate the asymmetry AsTin(2φ−φS ) at the COMPASS kinematics within the TMD factorization [2]. We take into account the scale dependence of the pion Boer-Mulders function and the proton transversity function, for which we consider two different parameterizations on the nonperturbative Sudakov form factor

The TMD evolution of distribution functions

Nc e2q q

Conclusion