Probing Majorana neutrinos with double-β decay.

Area of Science:

• Particle Physics
• Nuclear Physics
• Cosmology

Background:

• Neutrinos potentially being Majorana fermions has significant implications for particle physics and cosmology.
• Neutrinoless double-beta (0νββ) decay is a key process linked to the Majorana nature of neutrinos, potentially explaining the matter-antimatter asymmetry in the universe.

Purpose of the Study:

• To search for the 0νββ decay of ⁷⁶Ge.
• To establish lower limits on the half-life of this decay process.
• To constrain the effective Majorana neutrino mass.

Main Methods:

• Operation of bare germanium detectors within an active liquid argon shield by the GERDA Collaboration.
• Accumulation of a total exposure of 82.4 kg⋅year of data.

Main Results:

• No signal consistent with 0νββ decay was observed.
• A lower half-life limit of T _1/2 > 0.9 × 10²⁶ years (90% confidence level) was derived.
• The experimental sensitivity, assuming no signal, reached 1.1 × 10²⁶ years.

Conclusions:

• The absence of a signal places stringent limits on the properties of neutrinos.
• Combined with other 0νββ decay searches, this study contributes to a sensitivity to the effective Majorana neutrino mass between 0.07 and 0.16 electron volts.