Two Isotopes for Neutrinoless double beta decaY search

Introduction

The TINY experiment will focus on the investigation of neutrinoless double beta decay (0n2b) with 96Zr and 150Nd isotopes. The search for 0n2b is a hot topic in particle physics, as the discovery of this rare nuclear process would establish the Majorana nature of neutrinos, fix the neutrino mass scale, and prove lepton number non-conservation, setting the grounds for new physics beyond the Standard Model.

Motivation

The current and near-future large-scale searches for 0n2b do not include the nuclei chosen for the TINY project, due to the unavailability of an appropriate scalable detector technology for these candidates. Both 96Zr and 150Nd have the crucial advantage of very high transition energy for the 0n2b process, which would allow obtaining a higher sensitivity to the effective Majorana mass compared to other isotope candidates.

Detector Development

Bolometric detectors with high energy resolution and active particle identification will be developed during the project execution.

1. 96Zr will be embedded into ZrO2 crystals, measured with thermal sensors, and coupled to auxiliary light detectors for active alpha particle rejection.
2. 150Nd will be studied with magnetic NdGaO3 absorbers and athermal phonon sensors.

Particle identification will be achieved via pulse shape discrimination. The first-ever efficient measurement of a magnetic compound as a bolometer will open the way to new opportunities in low-temperature particle detection.

Pilot Experiment

The TINY pilot experiment, consisting of a few kg scale underground demonstrator, will be able to set the best limits worldwide on the 0n2b half-lives for both 96Zr and 150Nd isotopes. Very low background in the region of interest will be obtained thanks to high transition energy and alpha rejection.

Future Perspectives

Not only will this project be competitive in the international context on a short time scale, but it will also open up new perspectives for ton-scale experiments that can surpass any existing technology in terms of sensitivity to the Majorana neutrino mass.