CMS Forward Calorimeters Phase II Upgrade

The Phase II Upgrade of the CMS forward calorimeters (electromagnetic and hadronic) originates from the fact that these calorimeters will not be sufficiently performant with the expected High Luminosity LHC conditions, planned to be started in 2025. The major challenge is to preserve/improve the high performance of the current forward detectors with new devices that can withstand the unprecedented radiation levels and disentangle the very large event pileup. CMS elected two design concepts to be presented in the Phase II Upgrade Technical Proposal Shashlik electromagnetic calorimeter + Hadronic Endcap Rebuild, and High Granularity Calorimeter. The former concept is based on reconstructing the endcap electromagnetic calorimeter with a shashlik design and replacing the active media of the endcap hadron calorimeter with radiation tolerant active media with a possibility to extend the coverage. The latter concept is concentrating on constructing a high granularity (both longitudinally and laterally) calorimeter system with silicon as the active medium for the electromagnetic and the front hadronic sections, and scintillator tiles in the backing hadronic section; all interleaved with absorbers in a sampling calorimeter setup. This report will concentrate on the need for the upgrade, major challenges and the proposed R and D concepts suitable for the Phase II upgrade framework. The existing designs will be discussed with recent information about the beam tests and laboratory measurements.