Large-Size LYSO:Ce Crystals for Electromagnetic Calorimetry in Space: Qualification and Characterisation of the HEPD-02 Energy Detector

Due to high density, high light yield, fast decay time and excellent energy resolution, L(Y)SO:Ce has been chosen for precision calorimeters in recent and future detectors. Space experiments like the currently operating HEPD-01 and the proposed HERD make use of LYSO crystals. In particular, HERD use the CaloCube concept, considering 30x30x30 mm 3 LYSO crystals to image the electromagnetic shower. On the other hand, HEPD-01 mounts nine crystals of 50x50x40 mm 3 . CMS barrel MIP timing layer proposed for the High-Luminosity LHC is based on 3x3x57 mm 3 LYSO bars to measure minimum ionizing particles with a time resolution of 30–50 ps. Last, LYSO detectors as large as 2x2x15 mm 3 are commercially available for spectroscopy and other applications. Although the fabrication of LYSO crystals is a well-established industrial process, ensuring high-level performance on large-size samples remains challenging, because the light response uniformity is affected by the variation of the Ce concentration along the crystal. The design of the High-Energy Particle Detector (HEPD-02) on board the CSES-02 mission includes two layers of large-size LYSO scintillating crystals, each consisting of 3 bars 150x50x25 mm 3 . In this contribution, we report the results of laboratory tests with radioactive sources and cosmic muons aimed at measuring the response uniformity and the detection efficiency of the crystal bars as a function of the energy deposit and the impact position.