Photon energy reconstruction with the MEG II liquid xenon calorimeter

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 an energy scale of the calorimeter with several calibration sources is also discussed to achieve a high resolution of 1.8 %.