Development of Scintillating Bolometer for Neutrinoless Double Beta Decay of ⁴⁸Ca

  Neutrinoless double beta decay (0vDBD) search is a way to prove the Majorana nature of neutrinos and to support leptogenesis scenarios. We are developing CaF₂ scintillating bolometers to search for 0vDBD of ⁴⁸Ca. The scintillating bolometers measuring heat and scintillation-light signals simultaneously can achieve an excellent energy resolution and to provide a clear particle identification between beta/gamma and alpha events.

  The target of the R&D setup is a 300 g CaF₂(Eu) crystal. The heat signals are read by a metallic magnetic calorimeter (MMC) thermally connected to a phonon collector film that is a thin metal layer evaporated on a surface of the crystal.  A light detector composed of a 2 inch Ge wafer and an MMC sensor is employed just above the crystal. An above ground experiment was carried out for simultaneous detection of heat and light signals from the crystal.  The measurement was compared with a Geant4 simulation of scintillation detection with realistic geometry of the detector components. It is noted that some portion of light is absorbed on the metal phonon collector. In this presentation, we report on the latest performance of the detector setup and a future plan to search for 0vDBD of ⁴⁸Ca using simultaneous  phonon-scintillation detection.