Evolution of the response of the CMS ECAL and possible design options for calorimetry at the High Luminosity LHC

The performance of the CMS electromagnetic calorimeter (ECAL) has been continuously monitored during LHC running. The evolution of this performance is a critical issue for the future, in particular for High-Luminosity LHC (HL-LHC) operation which is planned for 2022 and beyond. Work has started to assess the need for possible changes to the detector in order to maintain adequate performance in the high radiation environment of HL-LHC. In this paper, results from CMS running, beam tests and laboratory measurements on proton-irradiated crystals are combined to predict the performance of the current detector during the HL-LHC phase. Several options for the replacement of the CMS endcap calorimeters for HL-LHC running are presented.