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

BackgroundThe 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).
PurposeThe light output has non-uniformity along the length direction of the scintillator strip, which affects the resolution of the ScW ECAL. It is necessary to control the non-uniformity to a low level.
MethodsWe present the optimization of the scintillator units to improve the uniformity of the light output, including the light output distribution of the scintillator strips with different SiPM coupling configurations, and the impact of the coupling groove shape and dimension on the light output uniformity.
Results and conclusionThe results show that the non-uniformity of the scintillator unit with a runway-shaped coupling groove at the bottom-center of the strip can achieve 4% without reduction in the light output. Compared to the case of non-uniformity before optimization, the optimized uniformity improves the boson mass resolution about 23% based on the reconstruction of Higgs → γγ, which is comparable to the perfect homogeneous case.