Cluster time measurement with CEPC calorimeter

We have developed an algorithm dedicated to timing reconstruction in highly granular calorimeters (HGC). The performance of this algorithm is evaluated on an electromagnetic calorimeter (ECAL) with geometries comparable to the electromagnetic compartment (CE-E) of the CMS endcap calorimeter upgrade at HL-LHC and conceptual Particle Flow oriented ECAL’s for future Higgs factories. The time response of individual channel is parameterized according to the CMS experimental result (Akchurin et al. in Nucl Instrum Methods Phys Res Sect A Accel Spectrom Detect Assoc Equip 859:31, 2017). The particle Time-of-Flight (ToF) can be measured with a resolution of 5–20 ps for electromagnetic (EM) showers and 80–160 ps for hadronic showers above 1 GeV. The presented algorithm provides comparable reconstruction with the Ehit2 weighting strategy and can significantly improve the time resolution compared to a simple averaging of the fast component of the time spectrum. The effects of three detector configurations are also quantified in this study. ToF resolution depends linearly on the timing resolution of a single silicon sensor and improves statistically with increasing incident particle energy. The timing layers at depth of 6–9 radiation lengths provide higher timing performance for EM showers. A clustering algorithm that vetoes isolated hits improves ToF resolution.