Improved limit on neutrinoless double beta decay of $^{100}$Mo from AMoRE-I

TL;DR

This paper reports an improved lower limit on the half-life of neutrinoless double beta decay of $^{100}$Mo, achieved through the AMoRE-I experiment using scintillating molybdate crystals at underground facilities, constraining neutrino mass models.

Contribution

The study demonstrates the first large-scale application of AMoRE technology with 18 crystals, setting a new experimental lower limit on $^{100}$Mo neutrinoless double beta decay half-life.

Findings

No decay signal observed within the experimental sensitivity.

Established a new lower half-life limit of $2.9 imes 10^{24}$ years.

Constrained the effective Majorana neutrino mass to below 210-610 meV.

Abstract

AMoRE searches for the signature of neutrinoless double beta decay of $^{100}$Mo with a 100 kg sample of enriched $^{100}$Mo. Scintillating molybdate crystals coupled with a metallic magnetic calorimeter operate at milli-Kelvin temperatures to measure the energy of electrons emitted in the decay. As a demonstration of the full-scale AMoRE, we conducted AMoRE-I, a pre-experiment with 18 molybdate crystals, at the Yangyang Underground Laboratory for over two years. The exposure was 8.02 kg$\cdot$year (or 3.89 kg$_{\mathrm{^{100}Mo}}\cdot$year) and the total background rate near the Q-value was 0.025 $\pm$ 0.002 counts/keV/kg/year. We observed no indication of $0\nu\beta\beta$ decay and report a new lower limit of the half-life of $^{100}$Mo $0\nu\beta\beta$ decay as $ T^{0\nu}_{1/2}>2.9\times10^{24}~\mathrm{yr}$ at 90\% confidence level. The effective Majorana mass limit range is $m_{\beta\beta}<$(210--610) meV using nuclear matrix elements estimated in the framework of different models, including the recent shell model calculations.