Sivers and Boer-Mulders observables from lattice QCD

TL;DR

This paper presents the first lattice QCD calculations of TMD observables, linking lattice results to experimental effects like Sivers and Boer-Mulders functions using staple-shaped Wilson lines.

Contribution

It introduces a novel lattice QCD approach employing staple-shaped Wilson lines to access process-dependent TMD observables, including non-universal T-odd effects.

Findings

Calculated Sivers and Boer-Mulders shifts for SIDIS and DY.

Studied staple extent and evolution dependence of TMD observables.

Analyzed impact of staple-shaped Wilson lines on T-even quantities.

Abstract

We present a first calculation of transverse momentum dependent nucleon observables in dynamical lattice QCD employing non-local operators with staple-shaped, "process-dependent" Wilson lines. The use of staple-shaped Wilson lines allows us to link lattice simulations to TMD effects determined from experiment, and in particular to access non-universal, naively time-reversal odd TMD observables. We present and discuss results for the generalized Sivers and Boer-Mulders transverse momentum shifts for the SIDIS and DY cases. The effect of staple-shaped Wilson lines on T-even observables is studied for the generalized tensor charge and a generalized transverse shift related to the worm gear function g_1T. We emphasize the dependence of these observables on the staple extent and the Collins-Soper evolution parameter. Our numerical calculations use an n_f = 2+1 mixed action scheme with domain wall valence fermions on an Asqtad sea and pion masses 369 MeV as well as 518 MeV.