The Phase II upgrade of the LHCb calorimeter system

The Phase 2 LHCb Upgrade, which is now being developed by the LHCb Collaboration, is supposed to make LHCb able to work at high luminosity, up to 2 ċ 1034/cm2/s. The plan is to collect ∼300 fb−1 of data in a few years. The Phase 2 Upgrade will require a major revision of the LHCb Calorimeter system. The increased instantaneous and integrated luminosity will result in very high particle density and radiation doses in the areas close to the beam pipe. In these conditions, ECAL has to provide high quality energy and position measurements for electromagnetic showers, as well as separation of two nearby developing showers. Another requirement for the LHCb Phase 2 Upgrade ECAL is the ability to measure the time of arrival of the photon or electron with an accuracy of few tens of picoseconds. At high luminosity, such time measurement is a powerful tool helping to correctly assign electromagnetic showers to primary vertices. The choice for the central part of ECAL can be a sampling calorimeter with dense tungsten-based converter and radiation hard crystal scintillator. Concerning the particular structure type, it was found that the Spaghetti Calorimeter (SPACAL) concept meets all the requirements, including limits on radiation degradation, if its active elements are made of GAGG:Ce or YAG:Ce scintillators. The peripheral areas with moderate radiation doses can be instrumented with calorimeter modules based on plastic scintillator. A R&D; campaign was started to optimize the Upgrade 2 ECAL structure. It includes studies of scintillating materials, beam test studies of the performance of various ECAL module prototypes, and simulation studies to find the optimal detector layout, longitudinal segmentation and granularity. In this paper we present the R&D; results and the current status of the LHCb Calorimeter upgrade.