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We present the preliminary results of measurements of single spinasymmetries, $A_L$ for $W^\pm$ boson production in longitudinally polarized p+pcollisions at $\sqrt{s}=510$ GeV and measurements of cross section ratios,$\sigma _{W^+} / \sigma _{W^-}$, for $W^+,W^-$ boson production in $p+p$collisions at $\sqrt{s}$ = 500 and 510 GeV. The asymmetry measurements arebased on 246.2 pb$^{-1}$ of data taken in the RHIC 2013 run and the crosssection ratio measurements are based on 102 pb$^{-1}$ of data taken during RHIC2011 and 2012 runs by the STAR experiment. While the asymmetry results areshown as a function of the decay lepton pseudorapidity, $\eta_e$, the crosssection results are shown as a function of both $\eta_e$ and W boson rapidity,$y_W$ in the mid-rapidity region ($|\eta_e|<1$). At this kinematics, $W^\pm$single spin asymmetries provide a theoretically clean probe of the proton'spolarized quark and antiquark distributions and the W cross section ratioprovides sensitivity to unpolarized sea quark distributions at the scale of theW mass. The asymmetry results are consistent with recently published STAR$A^{W^\pm}_L$ results based on the data collected during RHIC 2011 and 2012runs which showed a preference for a sizable, positive up antiquarkpolarization in the range $0.05 < x < 0.2$. The new preliminary results can beconsidered as the most precise results of $A^{W^\pm}_L$ in the world to date,with uncertainties reduced by 40\% in comparison to the published results.

Measurement of $W^{\pm}$ single spin asymmetries and $W$ cross section ratio in polarized $p+p$ collisions at $\sqrt{s}=510$ GeV at STAR