The CMS ECAL Barrel Upgrade for High Precision Timing and Energy Measurements in HL-LHC

The Electromagnetic Calorimeter (ECAL) of the Compact Muon Solenoid (CMS) experiment will be upgraded for the High-Luminosity phase of the LHC (HL-LHC) to cope with the new, harsher conditions, in terms of luminosity and pileup. The current lead tungstate crystals avalanche photodiode detectors in the barrel region of the ECAL will remain, while the front-end and off-detector read-out electronics of the calorimeter will be upgraded. The new electronics will have to fulfill the requirements of the upgraded Level 1 hardware trigger system, in terms of increased latency and data bandwidth, in order to preserve detector performance despite the increased instantaneous luminosity. The upgrade will provide single crystal granularity for the hardware trigger and will enable a full read out of the detector. A crucial characteristic of the new design will be the ability to measure the time of electrons and photons with high precision, of the order of 30 ps for energies above 100 GeV. This excellent time resolution will improve the overall CMS physics performance under the expected pile-up conditions. The status of the ongoing R&D activities is presented, together with the latest beam test results with prototypes.