Transverse single-spin asymmetries of weak boson, Drell-Yan and prompt photon production at STAR

• Main Author: Fazio, Salvatore
• Format: Conference Proceeding
• Language: English
• ISSN: 0094-243X; 1551-7616
• DOI: 10.1063/1.4977153

Accessing the Sivers TMD function in proton+proton collisions through the measurement of transverse single spin asymmetries (TSSAs) in Drell-Yan and weak boson production is an effective path to test the fundamental QCD prediction of the non-universality of the Sivers function. Furthermore, it provides data to study the spin-flavor structure of valence and sea quarks inside the proton and to test TMD evolution of parton distributions. The TSSA amplitude, A N , has been measured at STAR in proton+proton collisions at s = 500  GeV , with a recorded integrated luminosity of 25 pb−1. Within relatively large statistical uncertainties, the current data favor theoretical models that include a change of sign for the Sivers function relative to observations in SIDIS measurements, if TMD evolution effects on the A N are small. RHIC plans to run collisions of transversely polarized proton+proton beams at s = 500  GeV in 2017, delivering an integrated luminosity of 400 pb−1. This will allow STAR to perform a precise measurement of TSSAs in both Drell-Yan and weak boson production, as well as other observables sensitive to the non-universality of the Sivers function via the Twist-3 formalism, e.g. the TSSA of prompt photons.