Response of a CMS HGCAL silicon-pad electromagnetic calorimeter prototype to 20–300 GeV positrons

The Compact Muon Solenoid Collaboration is designing a new high-granularity endcap calorimeter, HGCAL, to be installed later this decade. As part of development work, prototype system was built, with an electromagnetic section consisting 14 double-sided structures, providing 28 sampling layers. Each layer has hexagonal module, where multipad large-area silicon sensor glued between electronics circuit board and metal baseplate. pads approximately 1 cm$^2$ are wire-bonded the readout by custom integrated circuits. extensively tested beams at CERN's Super Proton Synchrotron in 2018. Based on data collected positrons, energies ranging from 20 300 GeV, measurements energy resolution linearity, position angular resolutions, shower shapes presented compared detailed Geant4 simulation.