Precise ^{136}Xe Double Beta Decay Measurement in PandaX-4T with Implications on the Nuclear Matrix Elements and...

Area of Science:

• Nuclear Physics
• Particle Physics
• Astroparticle Physics

Background:

• Double beta decay (ββ) is a rare nuclear process.
• It offers a unique window into physics beyond the Standard Model.
• The continuous spectrum of ββ decay is sensitive to new physics signatures.

Purpose of the Study:

• To precisely measure the two-neutrino double beta decay (2νββ) half-life of ^{136}Xe.
• To constrain parameters related to the ^{136}Xe 2νββ nuclear matrix element.
• To search for Majoron-emitting modes of ^{136}Xe ββ decay.

Main Methods:

• Analysis of ^{136}Xe ββ spectrum using 39.1±0.7 kg·yr exposure from the PandaX-4T experiment.
• Precise measurement of the 2νββ half-life.
• Calculation of the ξ_{31}^{2ν} parameter, representing the ratio of nuclear matrix element components.
• Search for Majoron-emitting modes by analyzing spectral shape.

Main Results:

• The most precise measurement of the ^{136}Xe 2νββ half-life: (2.14±0.05)×10^{21} years, with uncertainty reduced by a factor of 2.
• Measurement of ξ_{31}^{2ν} = 0.59_{-0.38}^{+0.41}, consistent with theoretical predictions.
• Establishment of the most stringent limit for the spectral index n=7 for Majoron-emitting modes.

Conclusions:

• The precise ^{136}Xe 2νββ half-life measurement significantly improves constraints on nuclear matrix elements.
• Results are consistent with the Standard Model and theoretical predictions for nuclear structure.
• The stringent limits on Majoron-emitting modes push the boundaries for searches of new physics.