Search for neutrinoless double-beta decay in 136Xe with EXO-200

Area of Science:

• Nuclear Physics
• Particle Physics
• Astroparticle Physics

Background:

• Neutrinoless double-beta decay is a hypothetical process that violates lepton number conservation.
• Its observation would prove the Majorana nature of neutrinos and provide insights into the matter-antimatter asymmetry in the universe.

Purpose of the Study:

• To search for neutrinoless double-beta decay (0νββ) of the isotope 136Xe.
• To set a lower limit on the half-life of this decay process.

Main Methods:

• Utilized the EXO-200 detector, a large liquid xenon time projection chamber.
• Analyzed data corresponding to an exposure of 32.5 kg·yr.

Main Results:

• No statistically significant excess of events was observed in the region of interest for 0νββ decay.
• A background rate of approximately 1.5×10⁻³ counts/(kg·yr·keV) was achieved within the ±1σ region.

Conclusions:

• Established a lower limit on the half-life of 136Xe neutrinoless double-beta decay: T(1/2)(0νββ)(136Xe) > 1.6×10²⁵ yr at 90% confidence level.
• Constrained the effective Majorana neutrino masses to be less than 140–380 meV, depending on theoretical calculations of nuclear matrix elements.