First results from a beam test of a high-granularity silicon-based calorimeter for CMS at HL-LHC

A prototype of the electromagnetic calorimeter for the CMS High Granularity Calorimeter that is being designed for the High Luminosity LHC (HL-LHC) was tested at the Fermilab Test Beam Facility. The detector consisted of 16 sampling layers of silicon sensors interspersed with tungsten plates, for a total thickness of 15.3 X₀. Each of the hexagonal sensors were sub-divided into 128 cells, predominantly hexagonal in shape, of area ∼ 1.1 cm². The analog signal from the 2048 cells was readout using the 64-channel SKIROC2 ASIC, developed by the OMEGA group for the CALICE collaboration. Data were collected with a custom data acquisition system developed for these tests. The detector was calibrated using signals obtained with 120 GeV protons. We report here the design of the prototype detector and the results obtained from analyzing the data collected in July 2016, with electron beams at energies ranging from 4 to 32 GeV.