Development of High-Reflectivity Mirrors for pfRICH in the EIC Experiment

The upcoming Electron-Ion Collider (EIC) at Brookhaven National Laboratory will collide electrons with protons and nuclei to explore the structure of hadronic matter. The electron-Proton/Ion Collider (ePIC) detector at Interaction Point 6 features the proximity-focusing Ring Imaging Cherenkov (pfRICH) subsystem, designed for particle identification (PID) in the backward pseudorapidity region, -3.5 < n < -1.5, crucial for accessing low-x and low-Q² physics. The pfRICH identifies high-energy final-state hadrons by measuring their Cherenkov photon emission angle in an aerogel radiator. To enhance photon detection, it uses high-reflectivity mirrors that redirect photons toward the sensors. Our project involves fabricating these mirrors via evaporative coating and assessing their optical performance. We present the fabrication method and preliminary reflectivity results from mirrors produced at Stony Brook University, achieving up to 90% reflectivity across the 300–600 nm range.