Precision Electromagnetic Calorimetry and Timing at the Large Hadron Collider*

The CERN Large Hadron Collider (LHC) has been operating at the high energy frontier, providing proton-proton collisions at high rates, for more than a decade. The LHC experiments have been designed to withstand the challenging radiation environment, while providing excellent detector performance. The electromagnetic calorimeter (ECAL) of the CMS detector is homogenous, fine-grained detector made of scintillating lead-tungstate crystals. The CMS ECAL was designed to provide excellent energy resolution for electrons and photons and was crucial in the discovery of the Higgs boson, in particular in the two photon and two Z boson channels. The LHC will soon be upgraded to the High Luminosity LHC (HL-LHC), which will provide unprecedented instantaneous and integrated luminosity in an even more difficult environment. To meet the challenges of HL-LHC, CMS is undergoing an extensive Phase-2 upgrade. The central, barrel portion of ECAL will largely remain intact, as the crystals were designed to be radiation-tolerant. However, the readout electronics of the ECAL barrel will be upgraded to accommodate the higher trigger rate and latency at HL-LHC. Moreover, the endcap portion of the ECAL will be removed due to the larger radiation damage in the forward regions, and it replaced with an entirely new detector, the High Granularity Calorimeter (HGCAL). HGCAL is an ambitious new calorimeter, utilizing silicon and plastic scintillator tiles as its sensing technology. It will have around 6.5 million detector channels, divided into 50 layers. Moreover, the CMS detector will incorporate an innovative new MIP Timing Detector (MTD) for HL-LHC. MTD is aimed at providing new and unique capabilities to CMS by measuring the time-of-arrival of minimum ionizing particles with a resolution of 30 - 40 ps at the beginning of HL-LHC operation. The information provided by the MTD will help disentangle ~200 nearly simultaneous pileup interactions occurring in each bunch crossing at LHC by enabling the use of 4D reconstruction algorithms. The MTD will be composed of an endcap timing layer (ETL), instrumented with low-gain avalanche diodes, as well as a barrel timing layer (BTL), based on LYSO:Ce crystals coupled to SiPMs. This talk will overview precision electromagnetic calorimetry and timing, including both the current LHC and the future at HL-LHC.