• calibration
• calorimeter
• high energy physics
• Mu2e
• optimization
• particle identification
• particle physics

This thesis deals with the perfomance optimization of the Electromagnetic Calorimeter in the Mu2e experiment.

Mu2e experiment at Fermilab will search for Charged Lepton Flavor Violation (CLFV) by looking for the neutrinoless coherent conversion of muons into electrons in the field of an Al nucleus (mu^{-}+Al\longrightarrow e^{-}+Al). The expected signal is a mono-energetic electron, named as Conversion Electron (CE), with an energy of E_{mu e}=104.97 MeV, corresponding to the muon mass corrected for the binding energy of the muonic atom and the nuclear-recoil energy.

If no events are observed in three years of data taking, Mu2e will set a limit on the ratio between the rate of the conversion of muons relative and the rate of the muon atomic captures of R_{mu e}<=5.6*10^{-17} at 90% C.L.

The current experimental limit was set by the SINDRUM II experiment (R_{mu e}< 7*10^{-13}): Mu2e aims to improve this limit by 4 orders of magnitude. In the Standard Model (SM), even extendend to include the finite neutrino masses, the process mu^{-}+N\longrightarrow e^{-}+N can occur at a conversion rate R_{mu e}<10^{-50}; nevertheless many extensions of the SM predict R_{mu e} in the range of 10^{-14}-10^{-18}.

Mu2e relies on a synergetic experimental apparatus consisting of a straw tube tracker, an Electromagnetic Calorimeter made of pure CsI crystals and a Cosmic Ray Veto (CRV).

Time and energy measurements of the Calorimeter play a fundamental role in the Mu2e events selection providing Particle Identification (PID) to reject cosmic muons that can mimic the CE signal: systematics on the background rejection depend on the accuracy of the calorimeter calibration.

The Monte Carlo simulations presented in this thesis show how cosmic muons can be used to calibrate the calorimeter time and energy measurements with the required accuracy. Cosmic muons have been generated using a complete description of the experimental hall. A dedicated trigger used to acquire calibration events has been studied. Cosmic muons are selected imposing cuts both on the energy deposited in the crystals and on the event topology. The specific energy loss dE/dX is used to equalize the energy response of each crystal. The muons time of flight and the average propagation time of photons along the crystal are used to align the T_0 time offset of each channel. The effect of the residual miscalibration on the energy and time resolution is negligible with respect to the resolution values measured at a test beam with a small scale prototype and simulated with the full Mu2e detector.

Using the calorimeter energy, time and position measurement, a new calorimeter PID technique, based on a Boosted Decision Tree (BDT) algorithm, has been developed. The result is that the calorimeter is able to provide the required muon rejection factor while keeping the efficiency on conversion electrons above 90%.