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Description
CRILIN is a semi-homogeneous electromagnetic calorimeter based on Cherenkov lead fluoride (PbF$_2$) crystals, interspaced and read out by UV-extended SiPM matrices. CRILIN features high transverse granularity and longitudinal segmentation, with five layers of 1.3×1.3×4 cm$^3$ crystals.
Test beams demonstrated a time resolution of about 20 ps for energies as low as 5 GeV. Despite pure Cherenkov emission, the light yield was measured to be about 0.3 p.e./MeV, increasing up to 0.5 p.e./MeV with larger-pixel SiPMs, corresponding to a photo-statistics term of $4.5\%/\sqrt{E}$. Radiation hardness campaigns showed good performances after 10 kGy/year dose and $10^{14}$ neutrons/cm$^2$/year fluences.
Originally conceived for the muon collider, CRILIN is now being explored for electron-positron colliders, focusing on FCC-ee. The excellent timing resolution and granularity are a key asset not only for flavor physics performance but also for enhancing particle flow 5D reconstruction.
Although dual readout is not implemented, offline compensation is achieved by exploiting the longitudinal segmentation and the differences in electromagnetic and hadronic components shower profiles. For this reason, a ParticleNet regression was trained on simulation, showing competitive performances with respect to dual readout calorimetry.
A full-containment ECAL module will be tested in summer 2026 at CERN, with electron and pion beams, to validate electromagnetic energy resolution and hadronic energy reconstruction. The prototype features important technological developments, such as an aluminum alveolar mechanical structure, off-detector front-end electronics, and Kapton strips for SiPMs readout in longitudinally segmented arrangements, with as little as 2 mm external thickness outside the crystals in the transverse direction.