ZnMoO4: A promising bolometer for neutrinoless double beta decay searches

We investigate the performances of two ZnMoO4 scintillating crystals operated as bolometers, in view of a next generation experiment to search the neutrinoless double beta decay of 100Mo. We present the results of the α vs β/γ discrimination, obtained through the scintillation light as well as through the study of the shape of the thermal signal alone. The separation obtained at the 2615 keV line of 208Tl is 8σ, using the heat-light scatter plot, while it exceeds 20σ using the shape of the thermal pulse alone. The achieved FWHM energy resolution ranges from 2.4 keV (at 238 keV) to 5.7 keV (at 2615 keV). The internal radioactive contaminations of the ZnMoO4 crystals were evaluated through a 407 h background measurement. The obtained limit is <32 μBq/kg for 228Th and 226Ra. These values were used for a Monte Carlo simulation aimed at evaluating the achievable background level of a possible, future array of enriched Zn100MoO4 crystals.

► The ZnMoO4 crystals permit alpha discrimination from the pulse shape analysis.
► ZnMoO4 crystals show an excellent energy resolution.
► ZnMoO4 crystals are extremely radiopure.
► A medium sized (30 kg) tower-like double beta experiment based on ZnMoO4 will show a zero background in the ROI.