Speaker
Salvatore Fazio
(Brookhaven National Laboratory)
Description
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 the TMD evolution of parton distributions.
The TSSA amplitude, $A_{N}$, has been measured at STAR in proton+proton collisions at $\sqrt{s} = 500$~GeV, with a recorded integrated luminosity of $25~\text{pb}^{-1}$.
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 $\sqrt{s} = 510$~GeV in 2017, delivering an integrated luminosity of $400~\text{pb}^{-1}$. This will allow STAR to perform a precise measurement of TSSAs in both Drell-Yan and weak boson production. The present status and future plans for the Sivers function program at STAR will be discussed 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.
Primary author
Salvatore Fazio
(Brookhaven National Laboratory)
