Prospects for a precision timing upgrade of the CMS PbWO$_{4}$ crystal electromagnetic calorimeter for the HL-LHC

The upgrade of the Compact Muon Solenoid (CMS) crystal electromagnetic calorimeter (ECAL), which will operate at the High Luminosity Large Hadron Collider (HL-LHC), will achieve a timing resolution of around 30 ps for high energy photons and electrons. In this talk we will discuss the benefits of precision timing for the ECAL event reconstruction at HL-LHC. Simulation studies on the timing properties of PbWO crystals, as well as the impact of the photosensors and the readout electronics on the timing performance, will be presented. Test beam studies on the timing performance of PbWO$_{4}$ crystals with various photosensors and readout electronics will be shown.