  The Mu2e experiment at Fermilab searches for the charged-lepton flavor
violating neutrino-less conversion of a negative muon into an electron in the
field of a aluminum nucleus. The dynamic of such a process is well modeled by a
two-body decay, resulting in a monoenergetic electron with an energy slightly
below the muon rest mass (104.967 MeV). The calorimeter of this experiment
plays an important role to provide excellent particle identification
capabilities and an online trigger filter while aiding the track reconstruction
capabilities. The baseline calorimeter configuration consists of two disks each
made with about 700 undoped CsI crystals read out by two large area UV-extended
Silicon Photomultipliers. These crystals match the requirements for stability
of response, high resolution and radiation hardness. In this paper we present
the final calorimeter design.
