  Over the past several years the STAR experiment at RHIC has been contributing
to our understanding of the proton structure. Through its instrumentation, STAR
is well equipped to measure $W \rightarrow \nu + e$ in $\sqrt{s}$ = 500/510 GeV
proton-proton collisions at mid-rapidity (-1.1 $\le \eta \le $ 1.1) . The $W$
cross section ratio ($W^+/W^-$) is sensitive to unpolarized $u$, $d$,
$\bar{u}$, and $\bar{d}$ quark distributions. At these kinematics, STAR is able
to measure the quark distributions near Bjorken-$x$ values of 0.1. The RHIC
runs in 2011, 2012 and 2013 at $\sqrt{s}$ = 500/510 GeV saw a significant
increase in delivered luminosity from previous years. This resulted in a total
data sample being collected of about 352 pb$^{-1}$ of integrated luminosity.
The increased statistics will lead to a higher precision measurement of the
$W^+/W^-$ cross section ratio than was previously measured by STAR's 2009 run,
as well as allow for a measurement of its $\eta$ dependence at mid-rapidity.
Presented here is an update of the $W$ cross section ratio analysis from the
STAR 2011, 2012 and 2013 runs.
