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Precise ^{136}Xe Double Beta Decay Measurement in PandaX-4T with Implications on the Nuclear Matrix Elements and
Zhe Yuan1, Zihao Bo2, Wei Chen2
1Key Laboratory of Nuclear Physics and Ion-beam Application (MOE), Institute of Modern Physics, Fudan University, Shanghai 200433, China.
Abstract:
The continuous spectrum of double beta decay (ββ) provides a sensitive probe to test the predictions of the standard model and to search for signatures of new physics beyond it. We present a comprehensive analysis of the ^{136}Xe ββ spectrum utilizing 39.1±0.7 kg·yr of ^{136}Xe exposure from the PandaX-4T experiment. The analysis yields the most precise measurement to date of the ^{136}Xe two-neutrino double beta decay (2νββ) half-life, (2.14±0.05)×10^{21} years, the uncertainty of which is reduced by a factor of 2 compared to our previous result. We measure the parameter ξ_{31}^{2ν}, defined as the ratio between the subleading and leading components of the ^{136}Xe 2νββ nuclear matrix element, to be 0.59_{-0.38}^{+0.41}, which is consistent with theoretical predictions. We also search for Majoron-emitting modes of ^{136}Xe ββ, establishing the most stringent limit for the spectral index n=7.
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