Description
The $J/\psi$ particle is a spin-1 charmonium state with significant decay fraction towards lepton pairs. The distribution of decay particles from the $J/\psi$ is influenced by its spin alignment, which provides insights into different production mechanisms. SeaQuest, a fixed target experiment at Fermilab, was designed to observe muon pairs from charmonium and Drell-Yan production in $pp$ and $pd$ interactions. The dimuons, produced from $J/\Psi\rightarrow\mu^+\mu^-$ decays, recorded by SeaQuest can be utilized to examine the spin alignment of the $J/\psi$ particle. In addition to the desired dimuon signals, the recorded data also includes combinations of two muon tracks that do not originate from a common physics vertex. We present an event-mixing method that accurately calculates this combinatorial background with appropriate normalization. This method can be extended for use in other experiments that observe dilepton pairs.