Optical Characterization of Window Materials for the J-PARC MARQ RICH Aerogel Radiator

The J-PARC E50 experiment aims at spectroscopic studies of charmed baryons. A Ring-Imaging Cherenkov (RICH) detector is being developed for particle identification (PID) in the MARQ spectrometer for E50. Due to the limited number of photons produced by Cherenkov radiators, maximizing light transmission through all detector components is essential for optimal performance. We have investigated the optical properties of various window materials for the silica aerogel radiator to identify the best choice for light throughput. Using a spectrometer at Osaka University and a custom light-detector setup, we measured the reflectance, absorption, and transmission of acrylic sheets, including samples with and without anti-reflective coatings. These measurements were compared with the Cherenkov emission spectrum and the known and measured absorption characteristics of the aerogel. We will present our results, which, combined with our review of existing data on different acrylics, have led us to select UV-transparent acrylic as the ideal window material. This research directly informs the material choice for the MARQ RICH to improve its photon detection efficiency.