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Searching for new physics with $^{136}$Xe double beta decay spectrum in PandaX-4T

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, Yang Zhang, Yingxin Zhang, Yuanyuan Zhang, Li Zhao, Kangkang Zhao, Jifang Zhou, Jiaxu Zhou, Jiayi Zhou, Ning Zhou, Xiaopeng Zhou, Zhizhen Zhou, Chenhui Zhu

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 $37.8 \pm 0.6$ kg$\cdot$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 two 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 $n=7$.

Searching for new physics with $^{136}$Xe double beta decay spectrum in PandaX-4T

Abstract

The continuous spectrum of double beta decay () 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 Xe spectrum utilizing kgyr of Xe exposure from the PandaX-4T experiment. The analysis yields the most precise measurement to date of the Xe two-neutrino double beta decay () half-life, years, the uncertainty of which is reduced by a factor of two compared to our previous result. We measure the parameter , defined as the ratio between the subleading and leading components of the Xe nuclear matrix element, to be , which is consistent with theoretical predictions. We also search for Majoron-emitting modes of Xe , establishing the most stringent limit for the spectral index .

Paper Structure

This paper contains 5 equations, 4 figures, 3 tables.

Figures (4)

  • Figure 1: Spectra for $G_{0}^{2\nu}$, $G_{2}^{2\nu}$, and the Majoron-emitting $\beta\beta$ modes with $n$ = 1, 2, 3, and 7, respectively. Detector response model is taken into account.
  • Figure 2: The SS data spectra and the fit for the $^{136}$Xe $2\nu\beta\beta$ half-life are shown for Run0 (top) and Run1 (bottom) from 20 keV to 2800 keV with a bin size of 4 keV. The horizontal axis represents the reconstructed energy in the data. Xe$^{*}$ includes the contributions from $^{124}$Xe, $^{125}$Xe, $^{127}$Xe, $^{129m}$Xe, $^{131m}$Xe, and $^{133}$Xe. The lower panel shows the residuals together with $\pm 1 \sigma$, $\pm 2 \sigma$ and $\pm 4 \sigma$ bands.
  • Figure 3: Two-dimensional profile likelihood scan for $^{136}$Xe $2\nu\beta\beta$ rate and $\xi_{31}^{2\nu}$. The black dot indicates the best-fit value of $\xi_{31}^{2\nu} = 0.59^{+0.41}_{-0.38}$. The contours correspond to the 68.3$\%$, 90$\%$, 95.4$\%$, and 99.7$\%$ CL.
  • Figure 4: Spectra fits with Majoron-emitting $\beta\beta$ decay signals ($n=7$). The figure is the same as Fig. \ref{['fig:fitresult_DBD']} but with the upper limits (90% CL) of signals illustrated as hatched histograms. The lower panel shows the residuals together with $\pm 1 \sigma$, $\pm 2 \sigma$ and $\pm 4 \sigma$ bands.