Measurements of $W$ and $Z/\gamma^*$ cross sections and their ratios in $pp$ collisions at STAR*

While the unpolarized valence quark ($d$ and $u$) distributions are well determined from DIS experiments, the sea quark distributions, $\bar{d}$ and $\bar{u}$, are much less constrained, in particular, near the valence region.

Measurements of $W^+/W^-$ production ratio in $pp$ collider experiments, such as the STAR experiment at RHIC, are sensitive to the $\bar{d}/\bar{u}$ ratio at a large $Q^2$ set by the $W$ mass.

This talk will discuss the recently published $W$ and $Z/\gamma^*$ cross section measurements via lepton-decay tagging, using the STAR $pp$ collision data at a center-of-mass energy of $\sqrt{s} = 510\,\mathrm{GeV}$ collected during the years 2011-2013, corresponding to an integrated luminosity of $\sim350\,\mathrm{pb^{-1}}$.

The present talk will also discuss preliminary results based on an additional $pp$ data set at $\sqrt{s} = 510\,\mathrm{GeV}$ collected in 2017, corresponding to an integrated luminosity of $\sim350\,\mathrm{pb^{-1}}$.