Search for Majoron-like particles with CUPID-0

We present the first search for the Majoron-emitting modes of the neutrinoless double β decay (0νββχ0) using scintillating cryogenic calorimeters. We analyzed the CUPID-0 Phase I data using a Bayesian approach to reconstruct the background sources activities, and evaluate the potential contribution of the Se82 0νββχ0. We considered several possible theoretical models which predict the existence of a Majoron-like boson coupling to the neutrino. The energy spectra arising from the emission of such bosons in the neutrinoless double β decay have spectral indices n=1, 2, 3, or 7. We found no evidence of any of these decay modes, setting a lower limit (90% of credibility interval) on the half-life of 1.2×1023 yr in the case of n=1, 3.8×1022 yr for n=2, 1.4×1022 yr for n=3 and 2.2×1021 yr for n=7. These are the best limits on the 0νββχ0 half-life of the Se82, and demonstrate the potentiality of the CUPID-0 technology in this field.