The development of a cryogenic detector with CaMoO₄ crystals for neutrinoless double beta decay search

The search for neutrinoless double beta decay (0νββ) is a key experiment for evaluating the mass of the neutrino and for determining the Majorana/Dirac nature of neutrinos. A scintillating CaMoO₄ crystal is a good material for use in investigating 0νββ with cryogenic detectors. The high transition energy (Q = 3034 keV) and nearly 10% natural abundance of ¹⁰⁰Mo, together with the scintillating property of the crystal, provide favorable conditions to search for 0νββ of ¹⁰⁰Mo. We report a prototype experiment operating at low temperatures using a CaMoO₄ crystal as a particle absorber. Prior to testing of isotopically-enriched ⁴⁰Ca¹⁰⁰MoO₄ crystals, a CaMoO₄ crystal with Mo of natural isotopic composition was tested. Using a metallic magnetic calorimeter as a temperature sensor, we achieved high energy resolutions for alpha particles and low-energy gamma rays. This experiment shows the feasibility of scaling up the crystal size to perform a high sensitivity search for 0νββ decay of ¹⁰⁰Mo.