Energy Evolution for the Sivers Asymmetries in Hard Processes

TL;DR

This paper studies the energy evolution of Sivers and Collins asymmetries in semi-inclusive deep inelastic scattering and Drell-Yan processes, using CSS evolution, and compares predictions with experimental data across various energies.

Contribution

It provides the first consistent description of Sivers and Collins asymmetries across SIDIS, Drell-Yan, and e^+e^- experiments by applying CSS evolution at one-loop order.

Findings

CSS evolution describes unpolarized cross sections well in the 2.4-100 GeV^2 range.

Consistent description of Sivers asymmetries in SIDIS and Drell-Yan data.

Predictions for di-hadron asymmetries at moderate energies are proposed.

Abstract

We investigate the energy evolution of the azimuthal spin asymmetries in semi-inclusive hadron production in deep inelastic scattering (SIDIS) and Drell-Yan lepton pair production in pp collisions. The scale dependence is evaluated by applying an approximate solution to the Collins-Soper-Sterman (CSS) evolution equation at one-loop order which is adequate for moderate Q^2 variations. This describes well the unpolarized cross sections for SIDIS and Drell-Yan process in the $Q^2$ range of 2.4-100GeV^2. A combined analysis of the Sivers asymmetries in SIDIS from HERMES and COMPASS experiments, and the predictions for the Drell-Yan process at RHIC at \sqrt{S}=200GeV are presented. We further extend to the Collins asymmetries and find, for the first time, a consistent description for HERMES/COMPASS and BELLE experiments with the evolution effects. We emphasize an important test of the evolution effects by studying di-hadron azimuthal asymmetry in e^+e^- annihilation at moderate energy range, such as at BEPC at \sqrt{S}=4.6GeV.