2025/12/04 by PandaX Collaboration, Yuan, Zhe, Bo, Zihao +109
#FOS: Physical sciences #High Energy Physics - Experiment (hep-ex) #Nuclear Experiment (nucl-ex)
paper · doi:10.48550/arxiv.2512.04849
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 136Xe ββ spectrum utilizing 37.8 ± 0.6 kg⋅yr of 136Xe exposure from the PandaX-4T experiment. The analysis yields the most precise measurement to date of the 136Xe two-neutrino double beta decay (2νββ) half-life, (2.14 ± 0.05) × 1021 years, the uncertainty of which is reduced by a factor of two compared to our previous result. We measure the parameter ξ312ν, defined as the ratio between the subleading and leading components of the 136Xe 2νββ nuclear matrix element, to be 0.59+0.41-0.38, which is consistent with theoretical predictions. We also search for Majoron-emitting modes of 136Xe ββ, establishing the most stringent limit for the spectral index n=7.