Evolution studies of the CMS ECAL endcap response and upgrade design options for High-Luminosity LHC

The operation of the CMS electromagnetic calorimeter (ECAL) during the High-Luminosity running of the LHC will be characterized by radiation levels and hadron fluences significantly beyond the design values. Moreover, a large increase in the number of proton-proton interactions per bunch crossing is expected with respect to the current conditions. Studies of the ECAL performance evolution based on LHC collision data, as well as irradiation and beam tests, indicate that its endcaps will need to be upgraded. An overview of the different replacement options under consideration is presented.