Constraining the Sea Quark Distributions Through W^+/- Cross Section Ratio Measurements at STAR

Over the past several years, parton distribution functions (PDFs) have become more precise. However there are still kinematic regions where more data are needed to help constrain global PDF extractions, such as the ratio of the sea quark distributions dbar/ubar near the valence region, x ≈ 0.1-0.3, where x is the fraction of the proton momentum carried by the parton. Furthermore, current measurements appear to suggest different high-x behaviors of this ratio. The W cross section ratio (W⁺/W^-) is sensitive to the unpolarized u, d, ubar, and dbar quark distributions at large Q² set by the W mass and could help shed light on this discrepancy. The STAR experiment at RHIC is well equipped to measure the leptonic decays of W bosons, in the mid-pseudorapidity range (|η|≤ 1), produced in proton + proton collisions at √s = 500/510 GeV. At these kinematics STAR is sensitive to quark distributions near x of 0.16. STAR can also measure W+/W- in a more forward region ranging from 1.0 < η < 1.5, which extends the sea quark sensitivity to higher x. RHIC runs from 2011 through 2013 have collected about 350 pb^-1 of integrated luminosity, and a 2017 run will provide an additional 350 pb^-1. This talk will present new preliminary results of the 2011-2013 W cross section ratios.