Complete event-by-event $\hat{I}\pm$/${\hat{I}}^3({\hat{I}}^2)$ separation in a full-size TeO${}_2$ CUORE bolometer by Neganov-Luke-magnified light detection

Abstract

In the present work, we describe the results obtained with a large ($\approx 133$ cm${}^3$) TeO${}_2$ bolometer, with a view to a search for neutrinoless double-beta decay ($0\hat{I}½{\hat{I}}^2{\hat{I}}^2$) of ${}^{130}$Te. We demonstrate an efficient $\hat{I}\pm$ particle discrimination (99.9\%) with a high acceptance of the $0\hat{I}½{\hat{I}}^2{\hat{I}}^2$ signal (about 96\%), expected at $\approx 2.5$ MeV. This unprecedented result was possible thanks to the superior performance (10 eV rms baseline noise) of a Neganov-Luke-assisted germanium bolometer used to detect a tiny (70 eV) light signal from the TeO${}_2$ detector, dominated by ${\hat{I}}^3$(${\hat{I}}^2$)-induced Cherenkov radiation but exhibiting also a clear scintillation component. The obtained results represent a major breakthrough towards the TeO${}_2$-based version of CUORE Upgrade with Particle IDentification (CUPID), a ton-scale cryogenic $0\hat{I}½{\hat{I}}^2{\hat{I}}^2$ experiment proposed as a follow-up to the CUORE project with particle identification. The CUORE experiment began recently a search for neutrinoless double-beta decay of ${}^{130}$Te with an array of 988 125-cm${}^3$ TeO${}_2$ bolometers. The lack of $\hat{I}\pm$ discrimination in CUORE makes $\hat{I}\pm$ decays at the detector surface the dominant background component, at the level of $\approx 0.01$ counts/(keV kg y) in the region of interest. We show here, for the first time with a CUORE-size bolometer and using the same technology as CUORE for the readout of both heat and light signals, that surface $\hat{I}\pm$ background can be fully rejected.

The second version reflects the changes made after PRC referees' comments