The Sivers asymmetry in $J/\Psi$ and lepton pair production at COMPASS

TL;DR

This paper discusses measuring the Sivers asymmetry in $J/ ext{ extbackslash}Psi$ and lepton pair production at COMPASS, providing predictions for large single spin asymmetries and addressing the sign change issue of the Sivers function.

Contribution

It offers the first predictions for the Sivers asymmetry in $J/ ext{ extbackslash}Psi$ production at COMPASS and addresses the sign change problem of the Sivers function in different processes.

Findings

Predicted large single spin asymmetry in $J/ ext{ extbackslash}Psi$ production.

Clarified the sign change issue of the Sivers function.

Provided experimental prospects for measuring the asymmetry.

Abstract

The abundant production of lepton pairs via $J/\Psi$ creation at COMPASS, $\pi ^\pm \, p^\uparrow \to J/\Psi \, X \to \ell^+ \ell^- X$, allows a measurement of the transverse Single Spin Asymmetry generated by the Sivers effect. The crucial issue of the sign change of the Sivers function in lepton pair production, with respect to Semi Inclusive Deep Inelastic Scattering processes, can be solved. Predictions for the expected magnitude of the Single Spin Asymmetry, which turns out to be large, are given.