Observation of the neutrinoless double-beta decay (0v2b) is a key to solve the neutrino absolute mass and the Majorana nature. Recent 0ν2b search experiments will test the neutrino mass region allowed in case of the inverted mass ordering, but oscillation experiments favor the normal ordering. For 0v2b search in the normal ordering region, a background-free search with a 1-ton scale large detector is essential. To realize such search, we are developing a new detector AXEL.
The AXEL is a high-pressure 136Xe gas TPC with using the electroluminescence (EL) process as a signal readout for good energy-resolution. The event topology is reconstructed by our unique tracking-plane of ELCC. The ELCC consists of four layers: anode Cu plate, rigid PTFE structure, ground mesh electrode, and photosensor array, with a cell structure. Drift electrons produced in the gas region are collected into each cell along the electric field, and they are linearly amplified by EL process. The ELCC promise high energy resolution and the scalability for the large volume.
With a 10 L size prototype chamber, we evaluated the feasibility study of ELCC; we achieved 0.8 - 1.0% of energy resolution with extrapolation to Q-value. For a precise measurement, we are constructing next prototype with 180 L size.
In this presentation, we will report the performance obtained with the 10 L prototype chamber, the latest upgrade status of a 180L-size prototype construction, and future prospect including deep learning.