Operating a PbWO₄ EM calorimeter in a harsh radiation environment

CEA Paris-Saclay, DPhP/IRFU

^* e-mail: marta.tornago@cern.ch

Published online: 7 March 2025

Abstract

The CMS Electromagnetic Calorimeter (ECAL) is the largest homogeneous calorimeter operating in a high energy physics experiment. During the course of the LHC Run 1, Run 2, and Run 3, ECAL has made essential contributions to the CMS physics program by precisely measuring the energy, position, and time of arrival of photons and electrons, and of hadronic jets. Among the masterpieces of physics results achieved with its excellent energy resolution is the observation of the Higgs boson in its two photon decay in 2012, and the precise measurement of its properties.

Operating a lead-tungstate scintillating calorimeter to such high precision and in a harsh radiation environment requires full control of the environmental conditions, such as temperature and bias voltages of the photodetectors, and a continuous correction of the crystal response changes. This paper focuses on the challenges faced over the recent Run 3 years – experiencing the largest instantaneous luminosity up to now – and describes the calibration techniques developed and the achieved results, also including the evolution of the monitoring system in preparation of the High Luminosity phase of the LHC.