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

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${}_{{}^{100}\mathrm{Mo}}\cdot$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 $0\hat{I}½{\hat{I}}^2{\hat{I}}^2$ decay and report a new lower limit of the half-life of ${}^{100}$Mo $0\hat{I}½{\hat{I}}^2{\hat{I}}^2$ decay as $T_{1/2}^{0\hat{I}½}>2.9\times 10^{24}\mathrm{yr}$ at 90\% confidence level. The effective Majorana mass limit range is $m_{{\hat{I}}^2{\hat{I}}^2}<$(210--610) meV using nuclear matrix elements estimated in the framework of different models, including the recent shell model calculations.

7 pages, 5 figures