Speaker
Dr
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 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 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~pb$^{-1}$. Within relatively large statistical uncertainties, the current data favor theoretical models that include change of sign for the Sivers function relative to observations in SIDIS measurements, if TMD evolution effects are small. RHIC plans to run proton+proton collisions of transversely polarized beams at $\sqrt{s}= 510$~GeV in 2017, delivering an integrated luminosity of 400~pb$^{-1}$.
This will allow STAR to perform a precise measurement of TSSAs in both weak boson and Drell-Yan production as well as other observables sensitive to the non-universality of the Sivers function via Twist-3, e.g. the TSSA of direct photons.
Author
Dr
Salvatore Fazio
(Brookhaven National Laboratory)
