A feasibility experiment at RHIC to measure the analyzing power for Drell-Yan production (ANDY)

TL;DR

This paper discusses a feasibility experiment at RHIC to measure the analyzing power for Drell-Yan production, aiming to test the predicted sign change of the Sivers function and inform future upgrades.

Contribution

It presents the experimental setup, current achievements, and future plans for measuring the Sivers function sign change in Drell-Yan production at RHIC.

Findings

Initial experiment configuration established

Progress made towards measuring analyzing power

Future upgrade requirements identified

Abstract

Large transverse single spin asymmetries (SSA) were measured for pions produced in pp-collisions up to RHIC energies. Sizeable SSA were also found in semi-inclusive deep inelastic scattering (SIDIS). Theory can explain such spin effects by going beyond collinear leading-twist perturbative QCD (pQCD) to include transverse momentum dependent (TMD) distribution and fragmentation functions. One of the most interesting TMDs is the Sivers function, which provides information on the correlation between the transverse spin of the nucleon and the transverse momentum distributions of the partons in the nucleon. It is particularly intriguing that theory predicts the Sivers function will change sign from SIDIS to Drell-Yan (DY) production. ANDY is aiming to test that prediction and to establish requirements for future upgrades at RHIC to study DY production. The experiment configuration, achievements to date, status and plans are discussed.