Performance of CMS High Granularity Calorimeter prototypes in beam test experiments

The present electromagnetic and hadronic calorimeters of the CMS experiment will be upgraded to cope with the harsh radiation environment and pileup conditions posed by the high luminosity operations of the LHC (HL-LHC) expected to start in 2027. The CMS collaboration has opted for a sampling calorimeter in the endcap sections of the detector, based on silicon and scintillator technologies, with unprecedented transverse and longitudinal segmentation to facilitate particle identification, particle-flow reconstruction and pileup rejection. As part of the ongoing development and testing phase of this High Granularity Calorimeter (HGCAL), prototypes of both the silicon and scintillator based calorimeter sections have been tested in 2018 in beams at CERN. We report on the performance of the prototype detectors in terms of stability of noise and pedestals, calibration with minimum-ionizing-particles (MIPs), and energy linearity and resolution for electrons and pions. We compare the measurements with a detailed GEANT4-based simulation.