Design and beam-test characterization of the CRILIN semi-homogeneous crystal calorimeter

Abstract CRILIN is a high-granularity semi-homogeneous electromagnetic calorimeter based on longitudinally segmented PbF 2 crystal matrices read out by UV-extended silicon photomultipliers. The concept combines fast Cherenkov response, fine transverse granularity, longitudinal shower information, and radiation tolerance for future lepton-collider experiments. This paper reports the construction of a large-area prototype and its performance measured in beam tests at the CERN SPS. The detector comprises five 7 × 7 PbF 2 crystal matrices, has a depth of about 22 X 0 , and is read out by four 3 × 3 mm 2   SiPMs per crystal integrated in a single electronic channel. Electron data between 10 and 120 GeV and dedicated 150 GeV muon data were used to characterize the detector response. A time resolution below 50 ps is achieved for electron energies above 10 GeV, reaching values below 20 ps above 60 GeV. The energy resolution is described by a stochastic term of (6.58±0.04)%/√( E /GeV) and a constant term of (0.23±0.02)%, with an additional noise contribution fixed from pedestal data. The longitudinal segmentation enables event-by-event corrections based on the reconstructed shower development, resulting in a significant improvement of the energy resolution. A light yield of approximately 0.54 photoelectrons/MeV is measured consistently using both electron showers and minimum-ionizing particles. A Geant4-based simulation incorporating the relevant experimental effects reproduces the measured energy resolution. These results validate the CRILIN architecture as a compact, fast, and longitudinally segmented electromagnetic calorimeter for future collider experiments.