Energy calibration of the MONUMENT's HPGe detectors during the ¹³⁶Ba and ⁷⁶Se runs

MONUMENT (Muon Ordinary capture for NUclear Matrix elemENT) measures Ordinary Muon Capture (OMC) on isotopes relevant for the neutrinoless double-beta decay (0νββ) searches. The uncertainty of the 0νββ nuclear matrix elements (NMEs) may limit the ability of next-generation searches to probe the effective Majorana neutrino masses down to the claimed few tens of meV. OMC is useful tool to study the 0νββ NMEs as it involves similar momentum transfers and allows one to experimentally probe the virtual transitions involved in the decay. To achieve its goals, MONUMENT needs to precisely reconstruct energy and intensity of the OMC-related gamma emission. In this talk, the energy calibration method using γs from calibration and background sources and ¹³⁶Ba muonic X-rays measured during the 2021 campaign at the PSI will be presented. The energy resolution and time stability studies will also be described. The talk will conclude by discussing the status and outlook of the total and partial capture rate analysis for ¹³⁶Ba and ⁷⁶Se, isotopes relevant for the two next-generation 0νββ searches, nEXO and LEGEND.