Electromagnetic calorimeter for belle II

Abstract

The electromagnetic calorimeter of the Belle II detector and its performance in the first SuperKEKB run during 2018 are described. It is a high-granularity calorimeter based on 8736 CsI(Tl) scintillating crystals. The scintillation light is detected by PIN photodiodes. Each calorimeter electronics readout channel includes a charge sensitive preamplifier attached to the crystal and a 2 MHz flash ADC followed by a wave form analysis (WFA) realized in FPGA which provides both amplitude and time reconstruction. Usage of the WFA reduces a contribution of the pile-up noise. High time resolution provides the beam background suppression. In the Belle II experiment the calorimeter is used for particle energy measurement, particle identification as well as for the collider luminosity measurement, it also contributes to the first-level trigger.