Design of a CsI(Tl) calorimeter for muonium-to-antimuonium conversion experiment

Abstract

The muonium-to-antimuonium conversion experiment (MACE) is proposed to search for charged lepton flavor violation and increase the sensitivity by more than two orders of magnitude compared to the muonium−antimuonium conversion spectrometer (MACS) experiment at PSI in 1999. A clear signature of this conversion is the positron produced from antimuonium decay. This paper presents a near-4\pi-coverage calorimeter designed for MACE, which can provide an energy resolution of 10.8% at 511 keV, and a signal efficiency of 78.3% for annihilation \gamma-ray events. Detailed Monte Carlo simulations using MACE offline software based on Geant4 are performed for geometry optimization, coincidence system design, background estimation, and benchmark detector validation.

Graphical abstract

Keywords

muonium-to-antimuonium conversion / charged lepton flavor violation / electromagnetic calorimeter / inorganic scintillator detector

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Declarations

The authors declare that they have no competing interests and there are no conflicts.

Acknowledgements

This work was supported by the National Natural Science Foundation of China (No. 12075326), the Natural Science Foundation of Guangzhou (No. 2024A04J6243), and the Fundamental Research Funds for the Central Universities (No. 23xkjc017) in Sun Yat-sen University. The authors would like to acknowledge the MACE Working Group for their invaluable teamwork. We also extend our gratitude to the colleagues at the SMOOTH lab, as well as to Ke Gong and Chenfeng Yang at Sun Yat-sen University, for their fruitful discussions and assistance related to this work. The simulation benefited greatly from the provision of computing resources by the National Supercomputer Center in Guangzhou. We are also grateful to the Southern Center for Nuclear-Science Theory (SCNT) at the Institute of Modern Physics in the Chinese Academy of Sciences for hospitality.

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