Search for Exclusive $W$ Boson Decays

The $W$ boson is an important part of the standard model for its role as a mediator of the weak force, and as such has been studied extensively. It's mass has been measured by LEP and Tevatron experiments. Since the first $W$'s were produced at the $Sp\bar{p}S$ in the 1980's the properties of the $W$ boson have been studied at the Tevatron, LEP, and the LHC. None of these studies have reconstructed an exclusive $W$ boson decay. We propose to search for the exclusive decay $W^\pm \to J/\psi D_s^\pm$ and related low-multiplicity, partially reconstructed decays. The chosen mode yields an all charged track final state where $J/\psi \to \mu^+\mu^-$ and $D_s^\pm \to K^+K^-\pi^\pm$. This final state has a good trigger signature, the $J/\psi \to \mu^+\mu^-$ decay, and a number of constraints to suppress background. We discuss the possible yields in data from the CDF and CMS experiments.