Time Measurement Calibration of HGCAL Prototype Modules

During the first run of the Large Hadron Collider (LHC)[1] between 2010-2012, the accelerator operated at 8TeV, and the data collected lead to the discovery of the Higgs boson. Run 2 took place between 2015-2018, and detailed studies are still being carried out on the Higgs boson and Standard Model (SM) processes as well as searches for physics beyond the SM. After the third long technical shutdown scheduled for 2024-2026, the High Luminosity-LHC (HL-LHC) operational phase will commence in the last quarter of 2026. The HL-LHC will integrate ten times more luminosity than the LHC, posing significant challenges for radiation tolerance and for dealing with the so-called pileup events for detectors in which the collisions happen. This is especially true for calorimeters in the forward region. Indeed, in high-luminosity colliders, a single crossing between 2 bunches of protons can produce several separate events, so-called pileup events with respect to the interaction of interest. With the increase in luminosity in 2026, the expected pile up will be in average 200, which is orders of magnitude higher than it is now at 40. As part of its HL-LHC upgrade program, the CMS Collaboration[2] is proposing to build a high granularity calorimeter (HGCAL) to replace the existing end-cap calorimeters. It must have the ability to withstand integrated radiation levels that are ten times higher than anticipated in the original CMS design. In addition, one of the main requirements for the HGCAL upgrade, is the time precision measurement of the high energy showers. It is important to obtain precise timing from each cell with a significant amount of deposited energy, aiding rejection of energy from pileup, and the identification of the vertex of the triggering interaction. Prototype modules for the future detector, have been constructed, based on 6-inch hexagonal silicon pad sensors. In 2017 and 2018, beam tests of different sampling configurations were conducted with the prototype modules: at DESY using electron beams and at CERN using beams of charged hadrons, electrons and muons.