Design and status of the Mu2e electromagnetic calorimeter

TL;DR

The paper discusses the design, development, and current status of the Mu2e electromagnetic calorimeter, which is crucial for particle detection and background suppression in the Mu2e experiment at Fermilab.

Contribution

It presents the detailed design, R&D efforts, and engineering status of the Mu2e calorimeter, including a baseline BaF2 crystal solution and an alternative CsI crystal setup.

Findings

Calorimeter aims for 5% energy resolution at 100 MeV.

Time resolution better than 500 ps achieved in prototypes.

Development of UV extended APDs and MPPCs for crystal readout.

Abstract

The Mu2e experiment at Fermilab aims at measuring the neutrinoless conversion of a negative muon into an electron and reach a single event sensitivity of 2.5x10^{-17} after three years of data taking. The monoenergetic electron produced in the final state, is detected by a high precision tracker and a crystal calorimeter, all embedded in a large superconducting solenoid (SD) surrounded by a cosmic ray veto system. The calorimeter is complementary to the tracker, allowing an independent trigger and powerful particle identification, while seeding the track reconstruction and contributing to remove background tracks mimicking the signal. In order to match these requirements, the calorimeter should have an energy resolution of O(5)% and a time resolution better than 500 ps at 100 MeV. The baseline solution is a calorimeter composed of two disks of BaF2 crystals read by UV extended, solar blind, Avalanche Photodiode (APDs), which are under development from a JPL, Caltech, RMD consortium. In this paper, the calorimeter design, the R&D studies carried out so far and the status of engineering are described. A backup alternative setup consisting of a pure CsI crystal matrix read by UV extended Hamamatsu MPPC's is also presented.