Photon energy reconstruction with the MEG II liquid xenon calorimeter

TL;DR

This paper details the methods for precise photon energy reconstruction in the MEG II liquid xenon calorimeter, achieving high resolution and background reduction crucial for detecting rare muon decays.

Contribution

It introduces waveform analysis techniques for photon energy reconstruction and multi-photon elimination in a high-rate environment, enhancing detector performance.

Findings

Background events reduced by 34% in the 48-58 MeV range

Achieved a photon energy resolution of 1.8%

Effective calibration methods for energy scale implemented

Abstract

The MEG II experiment searches for a charged-lepton-flavour-violating $\mu \to e \gamma$ with the target sensitivity of $6 \times 10^{-14}$. A liquid xenon calorimeter with VUV-sensitive photosensors measures photon position, timing, and energy. This paper concentrates on the precise photon energy reconstruction with the MEG II liquid xenon calorimeter. Since a muon beam rate is $3\text{-}5 \times 10^{7}~\text{s}^{-1}$, multi-photon elimination analysis is performed using waveform analysis techniques such as a template waveform fit. As a result, background events in the energy range of 48-58 MeV were reduced by 34 %. The calibration of the energy scale of the calorimeter with several calibration sources is also discussed to achieve a high resolution of 1.8 %.