Latest results from CUORE and prospects for CUPID

TL;DR

This work reviews the current status of the CUORE program and its prospects for CUPID, framing the search for neutrinoless double-beta decay as a test of lepton-number violation and Majorana neutrino physics. It highlights CUORE’s tonne-scale cryogenic bolometer approach with 988 TeO$_2$ crystals searching for $^{130}$Te decays near $Q_{\beta\beta}=2527.5$ keV, reporting a strong exposure ($\sim$2.9 tonne·yr) and a strict $0\nu\beta\beta$ limit ($T^{0\nu}_{1/2}>3.5\times10^{25}$ yr) along with a precise $2\nu\beta\beta$ measurement, enabled by a robust background model and excellent energy resolution ($\sim$7.54 keV FWHM). CUPID is proposed to upgrade this program by deploying 1596 Li$_2$MoO$_4$ crystals enriched in $^{100}$Mo, using Ge light detectors with Neganov-Trofimov-Luke amplification to achieve simultaneous heat and light readout for background discrimination, and aiming for a background index of $1.0\times10^{-4}$ counts/(keV·kg·yr) and a sensitivity to $m_{\beta\beta}$ in the 9–15 meV range over a decade of data. With staged deployment beginning around 2030 and full-scale operation by 2034, CUPID seeks to cover the inverted-hierarchy region and push towards discovery in the next generation of cryogenic calorimeters. The projected reach relies on leveraging CUORE’s infrastructure and proven performance, representing a significant advance in the search for Majorana neutrinos.

Abstract

The search for neutrinoless double beta decay (0$νββ$) is fundamental for investigating lepton-number violation, probing new physics beyond the Standard Model, and determining whether neutrinos are Majorana particles. CUORE (Cryogenic Underground Observatory of Rare Events), a cryogenic bolometric experiment at LNGS, studies 0$νββ$ in $^{130}$Te using 988 TeO$_2$ crystals. It is a milestone of cryogenic detector arrays with a tonne-scale detector operated for more than 7~years below 15~mK. Since 2017, CUORE has accumulated over 2.9~tonne-years of exposure, achieving one of the leading 0$νββ$ limits and one of the most precise two-neutrino double beta decay (2$νββ$) half-life measurements thanks to a detailed background reconstruction across a broad energy range. Building on CUORE's success, CUPID (CUORE Upgrade with Particle ID) aims to significantly enhance its 0$νββ$ discovery sensitivity to $10^{27}$ yr in $^{100}$Mo, covering the Inverted Hierarchy of neutrino masses. It will employ lithium molybdate (Li$_2$MoO$_4$) crystals enriched in $^{100}$Mo, alongside germanium light detectors with Neganov-Trofimov-Luke amplification, enabling simultaneous heat and light readout for enhanced background rejection. CUPID will reuse CUORE's cryostat and infrastructure. Current efforts focus on detector performance validation, sensitivity studies, and finalizing the experimental design to maximize physics reach. This work presents the latest CUORE results and outlines the key milestones toward CUPID's realization.

Figures (5)

• Figure 1: Schematic of CUORE's bolometric detector module.
• Figure 2: The CUORE energy spectrum for 2039.0 kg$\cdot$yr of TeO$_{2}$ exposure after each selection cut, the Q$_{\beta\beta}$ for $^{130}$Te is marked as a red line with shaded ROI. Figure reprinted from Ref. cuoreScience2025.
• Figure 3: Fit to the ROI spectrum. Figure reprinted from Ref. cuoreScience2025.
• Figure 4: Left: schematic view of a single CUPID floor with two side-by-side detector modules, each consisting of a Li$_{2}$MoO$_{4}$ absorber and a Ge light detector. Right: a single tower of 14 floors, or 28 detector modules. Figure reprinted from Ref. cupid2025cupid.
• Figure 5: Constraints on the effective Majorana neutrino mass ($m_{\beta\beta}$) as a function of the lightest neutrino mass ($m_{\rm{lightest}}$). Figure reprinted from Ref. cupid2025cupid.