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arXiv · 2512.04849

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

PandaX Collaboration·Zhe Yuan·Zihao Bo·Wei Chen·Xun Chen·Yunhua Chen·Chen Cheng·Xiangyi Cui·Manna Deng·Yingjie Fan·Deqing Fang·Xuanye Fu·Zhixing Gao·Yujie Ge·Lisheng Geng·Karl Giboni·Xunan Guo·Xuyuan Guo·Zichao Guo·Chencheng Han·Ke Han·Changda He·Jinrong He·Houqi Huang·Junting Huang·Yule Huang·Ruquan Hou·Xiangdong Ji·Yonglin Ju·Xiaorun Lan·Chenxiang Li·Jiafu Li·Mingchuan Li·Peiyuan Li·Shuaijie Li·Tao Li·Yangdong Li·Zhiyuan Li·Qing Lin·Jianglai Liu·Yuanchun Liu·Congcong Lu·Xiaoying Lu·Lingyin Luo·Yunyang Luo·Yugang Ma·Yajun Mao·Yue Meng·Binyu Pang·Ningchun Qi·Zhicheng Qian·Xiangxiang Ren·Dong Shan·Xiaofeng Shang·Xiyuan Shao·Guofang Shen·Manbin Shen·Wenliang Sun·Xuyan Sun·Yi Tao·Yueqiang Tian·Yuxin Tian·Anqing Wang·Guanbo Wang·Hao Wang·Haoyu Wang·Jiamin Wang·Lei Wang·Meng Wang·Qiuhong Wang·Shaobo Wang·Shibo Wang·Siguang Wang·Wei Wang·Xu Wang·Zhou Wang·Yuehuan Wei·Weihao Wu·Yuan Wu·Mengjiao Xiao·Xiang Xiao·Kaizhi Xiong·Jianqin Xu·Yifan Xu·Shunyu Yao·Binbin Yan·Xiyu Yan·Yong Yang·Peihua Ye·Chunxu Yu·Ying Yuan·Youhui Yun·Xinning Zeng·Minzhen Zhang·Peng Zhang·Shibo Zhang·Siyuan Zhang·Shu Zhang·Tao Zhang·Wei Zhang
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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 $39.1 \pm 0.7~\textrm{kg}\cdot\textrm{yr}$ 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, $(2.14 \pm 0.05) \times 10^{21}$ 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 $0.59^{+0.41}_{-0.38}$, 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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PandaX Collaboration, Zhe Yuan, Zihao Bo, Wei Chen, Xun Chen, Yunhua Chen, Chen Cheng, Xiangyi Cui, Manna Deng, Yingjie Fan, Deqing Fang, Xuanye Fu, Zhixing Gao, Yujie Ge, Lisheng Geng, Karl Giboni, Xunan Guo, Xuyuan Guo, Zichao Guo, Chencheng Han, Ke Han, Changda He, Jinrong He, Houqi Huang, Junting Huang, Yule Huang, Ruquan Hou, Xiangdong Ji, Yonglin Ju, Xiaorun Lan, Chenxiang Li, Jiafu Li, Mingchuan Li, Peiyuan Li, Shuaijie Li, Tao Li, Yangdong Li, Zhiyuan Li, Qing Lin, Jianglai Liu, Yuanchun Liu, Congcong Lu, Xiaoying Lu, Lingyin Luo, Yunyang Luo, Yugang Ma, Yajun Mao, Yue Meng, Binyu Pang, Ningchun Qi, Zhicheng Qian, Xiangxiang Ren, Dong Shan, Xiaofeng Shang, Xiyuan Shao, Guofang Shen, Manbin Shen, Wenliang Sun, Xuyan Sun, Yi Tao, Yueqiang Tian, Yuxin Tian, Anqing Wang, Guanbo Wang, Hao Wang, Haoyu Wang, Jiamin Wang, Lei Wang, Meng Wang, Qiuhong Wang, Shaobo Wang, Shibo Wang, Siguang Wang, Wei Wang, Xu Wang, Zhou Wang, Yuehuan Wei, Weihao Wu, Yuan Wu, Mengjiao Xiao, Xiang Xiao, Kaizhi Xiong, Jianqin Xu, Yifan Xu, Shunyu Yao, Binbin Yan, Xiyu Yan, Yong Yang, Peihua Ye, Chunxu Yu, Ying Yuan, Youhui Yun, Xinning Zeng, Minzhen Zhang, Peng Zhang, Shibo Zhang, Siyuan Zhang, Shu Zhang, Tao Zhang, Wei Zhang. 2026-04-09. Precise $^{136}$Xe Double Beta Decay Measurement in PandaX-4T with Implications on the Nuclear Matrix Elements and Majorons. https://doi.org/10.1103/v4c6-h6l6

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