Direct Measurement of Initial-State Energy Loss in Cold Nuclear Matter at Fermilab E906/SeaQuest

The study of parton energy loss in cold nuclear matter is crucial for understanding the nuclear medium properties in heavy ion experiments. The nuclear modification R_pA of the Drell-Yan process is a clean channel for measuring initial-state quark energy loss. The E906/SeaQuest experiment at the Fermilab Main Injector measures Drell-Yan, J/ψ, and ψ' production for p+A collisions with H, D, C, Fe, and W targets. The proton beam energy of 120 GeV (√s_NN=15 GeV) amplifies the expected energy loss effects relative to previous experiments with higher beam energies. The spectrometer acceptance is optimal for large target x where other nuclear effects, such as shadowing, are expected to be small. We present the current status of this measurement.