Optimization of the scintillator units for the CEPC scintillator-tungsten ECAL

Background The circular electron positron collider (CEPC) was proposed as a future Higgs/Z factory. A sampling calorimeter with scintillator-tungsten sandwich structure (ScW) is selected as one of the electromagnetic calorimeter (ECAL) options. Its active layers consist of plastic scintillator strip units with a thickness of 2 mm and a size of 5 × 45 mm2, read out by silicon photomultipliers (SiPM).