  The Mu2e experiment at Fermilab looks for Charged Lepton Flavor Violation
(CLFV) improving by 4 orders of magnitude the current experimental sensitivity
for the muon to electron conversion in a muonic atom. A positive signal could
not be explained in the framework of the current Standard Model of particle
interactions and therefore would be a clear indication of new physics. In 3
years of data taking, Mu2e is expected to observe less than one background
event mimicking the electron coming from muon conversion. Achieving such a
level of background suppression requires a deep knowledge of the experimental
apparatus: a straw tube tracker, measuring the electron momentum and time, a
cosmic ray veto system rejecting most of cosmic ray background and a pure CsI
crystal calorimeter, that will measure time of flight, energy and impact
position of the converted electron. The calorimeter has to operate in a harsh
radiation environment, in a 10-4 Torr vacuum and inside a 1 T magnetic field.
The results of the first qualification tests of the calorimeter components are
reported together with the energy and time performances expected from the
simulation and measured in beam tests of a small scale prototype.
