Precision Crystal Calorimetry at High Energy and High Luminosity CMS ECAL Performance at 13 TeV and Upgrade Test Beam studies

The electromagnetic calorimeter (ECAL) of the Compact Muon Solenoid Experiment (CMS) is operating at the Large Hadron Collider (LHC) in 2016 with proton-proton collisions at 13 TeV center-of-mass energy and at a bunch spacing of 25 ns. The instantaneous luminosity during this LHC Run II is expected to exceed 10^34 cm-2s-1 in routine operation. In this talk we present detailed performance results from the 2016 data taking period. At the higher center of mass energy and with the rapidly growing data set the performance at higher electron and photon energies becomes crucial. The CMS ECAL design ensures that its superb performance extends over a very wide range of energies up to electron and photon energies of 1 TeV and beyond. This is of crucial importance for physics searches beyond the standard model. We discuss how the triggering, event reconstruction and calibration of the ECAL detector is performing in this new regime. The impact of the ECAL performance on resonance searches in the mass range up to 1 TeV will be discussed. The running conditions in 2016 give a first impression on the challenging conditions we expect at the high luminosity LHC (HL-LHC). We review the design and R and D studies for the CMS ECAL crystal calorimeter upgrade and present first test beam studies. Particular challenges at HL-LHC are the harsh radiation environment, the increasing data rates and the extreme level of pile-up events, up to 200 simultaneous proton-proton collisions. We present test beam results on hadron irradiated PbWO crystals up to fluences expected at HL-LHC and the status of the new readout and trigger electronics R\ and D. The pile-up mitigation may be substantially improved by means of precision time tagging of calorimeter clusters, by associating them to primary vertices via 4D triangulation. We present test beam results on the precision timing potential of the CMS PbWO crystal calorimeter and discuss how the readout electronics may be adapted to exploit this performance in CMS.