What is it about?

The Mu2e experiment at Fermilab aims to search for the SM forbidden muon-to-electron conversion in Al muonic atoms. The signal signature consists of 104.96 MeV electrons, identified by a straw-tube tracker and a crystal calorimeter, made of two annular disks. In order to calibrate the calorimeter disks with minimum ionizing particles (MIP) before the installation, we have realized a Cosmic Ray Tagger (CRT) at Laboratori Nazionali di Frascati (LNF) of INFN. The CRT consists of two planes of eight 2.5 × 1.5 × 160 cm3 plastic scintillator (EJ-200) bars, coupled to SiPMs on both edges, so as to estimate longitudinal hit positions from time differences. 3D MIP tracking is achieved by reconstructing hit positions in the two planes, placed above and below the disks, and allows to calibrate the energy response, to align the time offsets, and to study the detector performances dependence along the crystals axis

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Why is it important?

Using the described technique, the CRT apparatus allows to track muons in 3D, by reconstructing the hit position in the two planes (placed above and below the disks), both on the transversal direction using the 2.5 mm × 8 segmentation and on the Z axis (with a longitudinal resolution of 1.6 cm at the center and 2.3 cm at the edges). The CRT has been completely assembled and characterized, showing good performances and 3D tracking capabilities. It is now going to be tested along with a large scale prototype of the calorimeter, in order to validate the calibration procedures

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This page is a summary of: Design, assembly and operation of a Cosmic Ray Tagger based on scintillators and SiPMs, Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment, January 2023, Elsevier,
DOI: 10.1016/j.nima.2022.167538.
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