Studying Cold Nuclear Matter with the MPC-EX of PHENIX

Highly asymmetric collision systems, such as $d$+Au, provide a unique environment to study cold nuclear matter. Potential measurements range from pinning down the modification of the nuclear wave function, i.e.~saturation, to studying final state interactions, i.e.~energy loss. The PHENIX experiment has enhanced the muon piston calorimeter (MPC) with a silicon-tungsten preshower, the MPC-EX. With its fine segmentation the MPC-EX extends the photon detection capability at 3$<|\eta|<$3.8. In this talk we review the current status of the detector, its calibration, and its identification capabilities using the 2016 $d$+Au dataset. We also discuss the specific physics observables the MPC-EX can measure.