The Compact Muon Solenoid (CMS) electromagnetic calorimeter (ECAL) is made of about 75,000 scintillating lead tungstate crystals arranged in a barrel and two endcaps. The scintillation light is read out by avalanche photodiodes (APDs) in the barrel and vacuum phototriodes in the endcaps. The fast signal from the crystal scintillation is amplified and sampled at 40 MHz by the on-detector electronics. This enables precise measurements of both the energy and timing of electromagnetic showers.
The High Luminosity upgrade of the LHC (HL-LHC) at CERN will provide unprecedented instantaneous and integrated luminosities of around 5.0–7.5×1034cm−2s−1 and 3 ab−1, respectively. An average of 140–200 collisions per bunch-crossing (‘pileup’) is expected. This poses a major challenge to the CMS event reconstruction. The CMS detector is therefore undergoing an extensive Phase-2 upgrade program to prepare for these demanding conditions. In the barrel region of the CMS ECAL, the lead tungstate crystals will continue to perform well. The APDs will also continue to be operational, with some increase in noise, which will be mitigated by reducing the temperature at which ECAL is operated. However, the entire readout and trigger electronics will need to be replaced to cope with the harsh conditions and increased trigger latency requirements at the HL-LHC. The upgraded detector will have a 25 times higher readout granularity and a sampling rate increase by a factor of 4. The upgraded ECAL will preserve the calorimeter energy resolution, and will significantly improve the time resolution for photons and electrons with energies above 10 GeV. In first part of this talk the status of the ongoing R&D activities for the ECAL upgrade, performance validation in beam tests and its estimated impact on some of the benchmark physics analyses will be presented.
The second part of the talk focuses on the setting up of a threshold Cherenkov detector at TIFR. To determine the shape of a portion of the cosmic ray muon energy distribution, we constructed a threshold Cherenkov detector sensitive to muons with energies between 1 and 5 GeV. We shall measure the integral muon intensity at nitrogen pressures between 1 and 10 atm, and fit the data based on a diffusion model of muon production by pions in the Earth’s atmosphere which describes the integral energy distribution as a power law with exponent −1. Through this, we will be able to infer the feasibility of using a threshold Cherenkov detector to accurately measure the shape of the cosmic ray muon energy distribution.
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