  The Mu2e experiment at Fermilab searches for the neutrino-less conversion of
a negative muon into an electron, with a distinctive signature of a
mono-energetic electron with energy of 104.967 MeV. The calorimeter is made of
two disks of pure CsI crystals, each read out by two custom large area
UV-extended SiPMs. It plays a fundamental role in providing excellent particle
identification capabilities and an online trigger filter while improving the
track reconstruction, requiring better than 10% energy and 500 ps timing
resolutions for 100 MeV electrons. In this paper, we present the status of
construction and the Quality Control (QC) performed on the produced crystals
and photosensors, the development of the rad-hard electronics, and the most
important results of the irradiation tests. Construction of the mechanics is
also reported. Status and plans for the calorimeter assembly and its first
commissioning are described.
