Improved Limit on Neutrinoless Double Beta Decay of ^{100}Mo from AMoRE-I.

AMoRE searches for the neutrinoless double beta decay using 100 kg 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. AMoRE-I is a demonstrator for the full-scale AMoRE, operated at the Yangyang Underground Laboratory for over two years. The exposure was 8.02  kg year (or 3.89  kg_{^{100}Mo} year), and the total background rate near the Q value was 0.025±0.002  counts/keV/kg/year. We observed no indication of 0νββ decay and report a new lower limit of the half-life of ^{100}Mo 0νββ decay as T_{1/2}^{0ν}>2.9×10^{24}  yr at 90% confidence level. The effective Majorana mass limit range is m_{ββ}<(210-610)  meV using nuclear matrix elements estimated in the framework of different models, including the recent shell model calculations.