Measurement of transverse single-spin asymmetry and cross-section ratios of kinematically fully reconstructed weak bosons in p+p collisions at $\sqrt{s}=500-510$~GeV at RHIC

28 Apr 2015, 16:40
25m
BALLROOM EAST ()

BALLROOM EAST

WG1 Structure Functions and Parton Densities WG6 Spin Physics

Speaker

Dr Salvatore Fazio (Brookhaven National Laboratory)

Description

We present the status and preliminary results on the analysis of kinematically fully reconstructed weak bosons at the STAR experiment. The transverse single spin asymmetry ($A_{N}$) has been measured in transversely polarized proton-proton collisions at $\sqrt{s} = 500$~GeV, with a recorded integrated luminosity of $25~\text{pb}^{-1}$. The measured observable is sensitive to the non-universality of the Sivers function, a fundamental prediction from the gauge invariance of QCD, and can provide a direct verification of transverse momentum dependent (TMD) distributions factorization. Furthermore, it provides an ideal tool to study the spin-flavor structure of valence and sea quarks inside the proton and to test the evolution of parton distributions. The $W^{+}/W^{-}$ cross section ratio has been measured in unpolarized proton-proton collisions at $\sqrt{s} = 500-510$~GeV, with a recorded integrated luminosity of $110~\text{pb}^{-1}$. The observable is sensitive to the flavor asymmetry in sea anti-quarks for Bjorken-$x > 0.1$ accessible at RHIC, providing an independent constraint on the large flavor asymmetry observed in Drell-Yan experiments, without the assumption of charge symmetry required in fitting the Drell-Yan data. In addition, the future opportunities for a precise measurement of $A_{N}$ in weak boson production at STAR will be discussed as well as other observables sensitive to the non universality of the Sivers function, i.e. direct photon $A_N$.

Primary author

Dr Salvatore Fazio (Brookhaven National Laboratory)

Presentation Materials