Research and Development Status for an Innovative Crystal Calorimeter for the Future Muon Collider

Accurate measurements of physical processes in high energy frontier experiments demand exceptional spatial, temporal, and energy precision to discern the physics behind high-energy particle jets. Calorimeters, like other detection systems, must be able to meet these increasingly challenging performance requirements. In the prospective TeV-scale Muon Collider, the primary hurdle in designing detectors and devising event reconstruction algorithms is the challenge posed by Beam-Induced Background (BIB). Nevertheless, it is conceivable to mitigate the impact of BIB on the Muon Collider's calorimeter by capitalizing on certain characteristics and ensuring key features such as high granularity, precise timing, longitudinal segmentation, and superior energy resolution. This is what the here described R&D is trying to achieve with an innovative semi-homogeneous electromagnetic calorimeter constructed from stackable and interchangeable modules composed of lead fluoride crystals (PbF 2 ). These modules are equipped with surface-mount UV-extended Silicon Photomultipliers (SiPMs) and are collectively referred to as the Crilin calorimeter (CRystal calorImeter with Longitudinal INformation). The challenge lies in making sure this calorimeter can operate effectively within an extremely harsh radiation environment, enduring an annual neutron flux of 10 14 n 1MeV / cm 2 and a total ionizing dose of 10 kGy. In this paper, the radiation tolerance measured in several irradiation campaigns is discussed and the timing performances during a test beam at CERN-H2 with 120-GeV electrons. Additionally a description of the latest prototype, Proto-1, is provided together with the results of the latest low-energy beam test at the LNF Beam Test Facility with 450 MeV electrons.