2016/07/06 by Salvatore Fazio, Fazio, Salvatore
Physics and Astronomy · #FOS: Physical sciences #High Energy Physics - Experiment (hep-ex) #Nuclear Experiment (nucl-ex) #hep-ex #nucl-ex
paper · pdf · doi:10.48550/arxiv.1607.01676
5 pages, preceedings of DID2016 to be published on PoS, conf id: 265. Talk given for the STAR Collaboration
arxiv created 2016/07/06 · arxiv updated 2016/07/07
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 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 are small. RHIC plans to run proton+proton collisions of transversely polarized beams at √(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 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 in the Twist-3 framework, e.g. the TSSA of direct photons.