  While the unpolarized parton distribution functions of the valence quarks
($d$ and $u$) are well determined from DIS experiments, the sea quark
counterparts, $\bar{d}$ 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, can probe
the $\bar{d}/\bar{u}$ ratio at a large $Q^2$ set by the $W$ mass. These
proceedings will discuss recent results of $W$ and $Z$ cross-section
measurements using the STAR $pp$ collision data at a center-of-mass energy of
$\sqrt{s} = 500/510\;\mathrm{GeV}$ collected in 2011, 2012, 2013 and 2017.
