Final design and current status of the Mu2e crystal calorimeter

The Mu2e experiment at Fermi National Accelerator Laboratory searches for the charged-lepton flavor violation neutrino-less conversion of a negative muon into an electron in the field of an aluminum nucleus. This decay results in a mono- energetic electron with energy slightly below the muon rest mass. The design of the Mu2e experiment has been studied to reach a single event sensitivity that is four order of magnitudes better than previous experiments.The Mu2e calorimeter plays an important role to provide particle identification and an online trigger filter. After a long period of R&D conducted both at INFN and Caltech on the different components, the final technical choice has been made and the calorimeter now consists of two disks, each one made by about 700 un-doped CsI crystals read out by two large area UV-extended silicon photomultipliers.In this paper, we describe the main components of the detector and the tests performed on a large size calorimeter prototype (Module 0) that has been equipped with final crystals, photosensors, front-end electronics and cooling system.