The Monument experiment: ordinary muon capture studies for $$0\nu \beta \beta $$ 0 ν β β decay

Abstract

Abstract The Monument experiment measures ordinary muon capture (OMC) on isotopes relevant for neutrinoless double-beta ( $$0\nu \beta \beta $$ 0 ν β β ) decay and nuclear astrophysics. OMC is a particularly attractive tool for improving the theoretical description of $$0\nu \beta \beta $$ 0 ν β β decay. It involves similar momentum transfers and allows testing the virtual transitions involved in $$0\nu \beta \beta $$ 0 ν β β decay against experimental data. During the 2021 campaign, Monument studied OMC on $$^{76}$$ 76 Se and $$^{136}$$ 136 Ba, the isotopes relevant for next-generation $$0\nu \beta \beta $$ 0 ν β β decay searches, like Legend and nEXO. The experimental setup has been designed to accurately extract the total and partial muon capture rates, which requires precise reconstruction of energies and time-dependent intensities of the OMC-related $$\gamma $$ γ rays. The setup also includes a veto counter system to allow selecting a clean sample of OMC events. This work provides a detailed description of the Monument setup operated during the 2021 campaign, its two DAQ systems, calibration and analysis approaches, and summarises the achieved detector performance. Future improvements are also discussed.