Impact of inter-gain calibration on positron energy measurement with the CMS High Granularity Calorimeter

Abstract

For the upcoming High Luminosity operations of the LHC (HL-LHC), one of the major upgrades for the CMS experiment is the replacement of existing endcap calorimeter with new High Granularity Calorimeter (HGCAL). The calorimeter is being upgraded in order to withstand the large amount of radiation exposure expected at the HL-LHC and at the the same time have a fine transverse and longitudinal granularity, and precise timing capabilities in order to separate the pile up contribution within individual events. The HGCAL will be based on silicon sensors and scintillator tiles directly readout with the silicon photomultipliers, and will have more than 6M independently readout channels. As a part of this upgrade program, a prototype system was exposed to beams of positrons with energies ranging from 20GeV to 300 GeV in beam test experiments carried out at CERN in October 2018. The prototype used consists of 14 double layered structures, each equipped with hexagonal silicon module along with 4 Skiroc2-CMS readout chips, in the electromagnetic section. This corresponds to ~3600 number of independent channels. The charged generated by particles traversing the sensors undergoes amplification, shaping and digitization before these are saved for offline analysis. To be able to cover a large dynamic range of charge from few fC to a few pC, two gain stages of the pulse shaper and a time-over-threshold measurements are used. This thesis summarizes calibrations of each of the intergain calibrations of these channels using charge injection method.