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We report new STAR measurements of the single-spin asymmetries AL for W + and W − bosons produced in polarized proton-proton collisions at √ s = 510 GeV as a function of the decay-positron and decay-electron pseudorapidity. The data were obtained in 2013 and correspond to an integrated luminosity of 250 pb −1 . The results are combined with previous results obtained with 86 pb −1 . A comparison with theoretical expectations based on polarized lepton-nucleon deep-inelastic scattering and prior polarized proton-proton data suggests a difference between the ū and d quark helicity distributions for 0.05 < x < 0.25. In addition, we report new results for the double-spin asymmetries ALL for W ± , as well as AL for Z/γ * production and subsequent decay into electron-positron pairs.

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