An Improved ZnMoO4 Scintillating Bolometer for the Search for Neutrinoless Double Beta Decay of Mo-100
Abstract
We present a prototype scintillating bolometer for the search for neutrinoless double beta decay of Mo-100, consisting of a single a parts per thousand 5 g ZnMoO4 crystal operated aboveground in the 20-30 mK temperature range. The scintillation light is read out by two thin Ge bolometers. The phonon signals are collected by NTD Ge thermistors. The ZnMoO4 crystal was grown with an advanced method (low-thermal-gradient Czochralski technique) and after purification of molybdenum. The results are very encouraging: the intrinsic energy resolution of the heat channel is a parts per thousand 800 eV FWHM, the alpha/beta rejection factor (crucial for background suppression) is better than 99.9% in the region of interest for double beta decay (a parts per thousand 3 MeV), and the radiopurity of ZnMoO4 looks substantially improved with respect to previous devices.