Abstract
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, AN, 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 AN 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.
Published Version
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