Search for Majoron-like particles with CUPID-0

We present the first search for the Majoron-emitting modes of the neutrinoless double beta decay (0 nu beta beta chi 0) 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 82Se 0 nu beta beta chi 0. We considered several possible theoretical models which predict the existence of a Majoronlike boson coupling to the neutrino. The energy spectra arising from the emission of such bosons in the neutrinoless double beta 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 x 1023 yr in the case of n = 1, 3.8 x 1022 yr for n = 2, 1.4 x 1022 yr for n = 3 and 2.2 x 1021 yr for n = 7. These are the best limits on the 0 nu beta beta chi 0 half-life of the 82Se, and demonstrate the potentiality of the CUPID-0 technology in this field.