This thesis discusses the process of extracting the longitudinal asymmetry,
$A_L^{W\pm}$, describing $W\rightarrow\mu$ production in forward kinematic
regimes. This asymmetry is used to constrain our understanding of the
polarized parton distribution functions characterizing $\bar{u}$ and $\bar{d}$
sea quarks in the proton. This asymmetry will be used to constrain the overall
contribution of the sea-quarks to the total proton spin. The asymmetry is
evaluated over the pseudorapidity range of the PHENIX Muon Arms, $2.1 <
|\eta|2.6$, for longitudinally polarized proton-proton collisions at 510 GeV
$\sqrt{s}$. In particular, I will discuss the statistical methods used to
characterize real muonic $W$ decays and the various background processes is
presented, including a discussion of likelihood event selection and the
Extended Unbinned Maximum Likelihood fit. These statistical methods serve
estimate the yields of $W$ muonic decays, which are used to calculate the
longitudinal asymmetry.