Search for Majorana Neutrinos with the Complete KamLAND-Zen Dataset

Area of Science:

• Particle Physics
• Nuclear Physics
• Astroparticle Physics

Background:

• Neutrinoless double-beta decay (0νββ) is a hypothetical process.
• Its observation would indicate that neutrinos are Majorana particles.
• This decay is searched for in ^{136}Xe.

Purpose of the Study:

• To search for 0νββ decay of ^{136}Xe.
• To improve the lower limit on the 0νββ decay half-life.
• To constrain the effective Majorana neutrino mass.

Main Methods:

• Utilized the full KamLAND-Zen 800 dataset.
• Analyzed 745 kg of enriched ^{136}Xe, corresponding to 2.1 ton·yr exposure.
• Improved background reduction techniques.

Main Results:

• Established a new lower limit for the 0νββ decay half-life: T_{1/2}^{0ν} > 3.8 × 10^{26} yr at 90% CL.
• Achieved a 1.7-fold improvement over the previous KamLAND-Zen limit.
• Derived upper limits on the effective Majorana neutrino mass (28–122 meV).

Conclusions:

• The search provides stringent constraints on 0νββ decay.
• The results contribute to understanding neutrino nature (Majorana vs. Dirac).
• Further research can refine these limits and neutrino mass estimations.