Speaker
Description
Future electron-positron colliders require jet energy resolutions of 3-4%, which is achievable using Particle Flow, placing stringent requirements on calorimeter energy resolution and granularity. To meet these requirements, a highly granular crystal electromagnetic calorimeter prototype has been developed based on long, cross-hatched crystal bars (12×2×2 cm³, BGO/BSO) and using SiPM readout. The homogeneous design is capable of measuring the energy and energy density of particles.
The prototype underwent a test beam campaign at the CERN PS-T9 beamline during June and July of 2025 to evaluate the performance of the calorimeter. The 2025 campaign was optimized to reduce the beam momentum spread by removing upstream instrumentation, resulting in a reduction of the measured stochastic term by around 30% compared to previous test beams. The physics programme included MIP calibration with muons and pions, electron energy scans from 0.1 to 10 GeV, and systematic studies of ASIC shaping time, SiPM overvoltage, and spill structure.
Results from the 2025 campaign will be presented: linearity within ~1% above 1 GeV and an energy resolution meeting the CEPC TDR target; particle identification with a boosted decision tree trained on simulation, reaching a ROC AUC of 0.996 without upstream detectors; event-by-event shower shape measurements, including a new measurement of shower fluctuations below 1 GeV; and extraction of absorber properties ( radiation length, critical energy, effective Molière radius), which were found to be comparable to PDG values for BGO. Machine-learning-based fast simulations of beamline simulation and full particle showers are also presented.
