Sivers Asymmetry for the proton and the neutron

TL;DR

This paper develops a formalism to evaluate the Sivers function in constituent quark models, applying it to the Isgur-Karl model, and compares the results with experimental data, including nuclear effects in neutron asymmetry extraction.

Contribution

It introduces a non-relativistic formalism for the Sivers function within constituent quark models and assesses nuclear effects in neutron asymmetry measurements.

Findings

Sizable Sivers effect with opposite signs for u and d flavors.

The Burkardt Sum Rule is largely satisfied.

Good agreement with experimental data after QCD evolution.

Abstract

A formalism is presented to evaluate the Sivers function in constituent quark models. A non-relativistic reduction of the scheme is performed and applied to the Isgur-Karl model. The results obtained are consistent with a sizable Sivers effect and the signs for the u and d flavor contributions turn out to be opposite. The Burkardt Sum Rule is fulfilled to a large extent. After the estimate of the QCD evolution of the results from the momentum scale of the model to the experimental one, a reasonable agreement with the available data is obtained. A calculation of nuclear effects in the extraction of neutron single spin asymmetries in semi-inclusive deep inelastic scattering off 3He is also described. In the kinematics of forth-coming experiments at JLab, it is found that the nuclear effects arising within an Impulse Approximation approach are under control.