The Mu2e undoped CsI crystal calorimeter

TL;DR

The paper describes the design, testing, and performance of the Mu2e experiment's CsI crystal calorimeter, which is crucial for particle identification, triggering, and track reconstruction in the search for muon-to-electron conversion.

Contribution

It presents the final design and validation results of the Mu2e calorimeter using a prototype tested with an electron beam, demonstrating its suitability for the experiment.

Findings

The prototype met timing and energy resolution requirements.

The chosen crystals and SiPMs passed thorough testing.

The design is ready for full-scale implementation.

Abstract

The Mu2e experiment at Fermilab will search for Charged Lepton Flavor Violating conversion of a muon to an electron in an atomic field. The Mu2e detector is composed of a tracker, an electromagnetic calorimeter and an external system, surrounding the solenoid, to veto cosmic rays. The calorimeter plays an important role to provide: a) excellent particle identification capabilities; b) a fast trigger filter; c) an easier tracker track reconstruction. Two disks, located downstream of the tracker, contain 674 pure CsI crystals each. Each crystal is read out by two arrays of UV-extended SiPMs. The choice of the crystals and SiPMs has been finalized after a thorough test campaign. A first small scale prototype consisting of 51 crystals and 102 SiPM arrays has been exposed to an electron beam at the BTF (Beam Test Facility) in Frascati. Although the readout electronics were not the final, results show that the current design is able to meet the timing and energy resolution required by the Mu2e experiment.