Upgrade Calorimetry towards high-granularity

The increase of the instantaneous luminosity during the High-Luminosity LHC (HL-LHC, phase 2) places stringent requirements on the detectors. New proposed calorimeters have to be designed to operate in the harsh radiation environment at the HL-LHC, where the average number of interactions per bunch crossing is expected to exceed 140. The LHC experiments have proposed various high-granularity calorimetric solutions. In this talk we focus on the new CMS high-granularity calorimeter (HGCAL), a highly granular sampling calorimeter with approximately six million silicon sensor channels ($\simeq$ 0.5 cm$^2$ and 1.1 cm$^2$ cells) and about four hundred thousand scintillator tiles read out by on-tile silicon photomultipliers. The HGCAL electronics, besides measuring energy and position of the energy deposits, are also designed to measure the time of particle arrival with a precision of about 50~ps. In HGCAL we have developed a reconstruction approach that fully exploits the granularity to achieve optimal electron, photon and hadron identification, as well as good energy resolution in the presence of pileup.