Extracting Drell-Yan Cross Section Ratios at Fermilab's E906 experiment

The ratios of cross sections for deep-inelastic processes in nuclei and in deuterium have shown us that the momentum distributions of partons in nucleons are modified in the nuclear environment. So far, studies have observed enhancements as well as suppression of these ratios in different Bjorken $x$ regions, resulting in well-known effects: shadowing, anti-shadowing, and the EMC effect. These variations tell us that the behavior of partons inside light nuclei is different compared to partons inside heavy nuclei. The E906 (SeaQuest) experiment at Fermilab studied the Drell-Yan (DY) production of dimuons by scattering a 120 GeV proton beam off fixed liquid H$_2$, D$_2$ and solid Fe, C, W targets. The data set collected provides a unique opportunity to study the cross section ratios (CSRs): Fe/D, C/D, W/D in terms of DY cross sections (frac{2}{A} frac{sigma_{pA}}{sigma_{pd}}). The E906 Collaboration has performed a study in the past to extract these CSRs and a set of preliminary results is already available. In this talk, we will present an updated version of the CSR extraction procedure in which we employ a newly developed technique to treat the combinatorial background. The results obtained by applying the updated procedure to the data collected in Run 2 and Run 3 ($sim$60\% of the total data) of SeaQuest along with a validation test of the new procedure and the systematic errors of the results will be discussed.