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Searching for Neutrinoless Double-Beta Decay of $^{136}$Xe with PandaX-4T

PandaX Collaboration, Shu Zhang, Zihao Bo, Wei Chen, Xun Chen, Yunhua Chen, Zhaokan Cheng, Xiangyi Cui, Yingjie Fan, Deqing Fang, Zhixing Gao, Lisheng Geng, Karl Giboni, Xunan Guo, Xuyuan Guo, Zichao Guo, Chencheng Han, Ke Han, Changda He, Jinrong He, Di Huang, Houqi Huang, Junting Huang, Ruquan Hou, Yu Hou, Xiangdong Ji, Xiangpan Ji, Yonglin Ju, Chenxiang Li, Jiafu Li, Mingchuan Li, Shuaijie Li, Tao Li, Zhiyuan Li, Qing Lin, Jianglai Liu, Congcong Lu, Xiaoying Lu, Lingyin Luo, Yunyang Luo, Wenbo Ma, Yugang Ma, Yajun Mao, Yue Meng, Xuyang Ning, Binyu Pang, Ningchun Qi, Zhicheng Qian, Xiangxiang Ren, Dong Shan, Xiaofeng Shang, Xiyuan Shao, Guofang Shen, Manbin Shen, Wenliang Sun, Yi Tao, Anqing Wang, Guanbo Wang, Hao Wang, Jiamin Wang, Lei Wang, Meng Wang, Qiuhong Wang, Shaobo Wang, Siguang Wang, Wei Wang, Xiuli Wang, Xu Wang, Zhou Wang, Yuehuan Wei, Weihao Wu, Yuan Wu, Mengjiao Xiao, Xiang Xiao, Kaizhi Xiong, Yifan Xu, Shunyu Yao, Binbin Yan, Xiyu Yan, Yong Yang, Peihua Ye, Chunxu Yu, Ying Yuan, Zhe Yuan, Youhui Yun, Xinning Zeng, Minzhen Zhang, Peng Zhang, Shibo Zhang, Tao Zhang, Wei Zhang, Yang Zhang, Yingxin Zhang, Yuanyuan Zhang, Li Zhao, Jifang Zhou, Jiaxu Zhou, Jiayi Zhou, Ning Zhou, Xiaopeng Zhou, Yubo Zhou, Zhizhen Zhou

TL;DR

This work reports a blind search for neutrinoless double-beta decay in $^{136}$Xe with the PandaX-4T detector, using a unified MeV-region analysis on Run0 and Run1 data corresponding to a combined exposure of 44.6 kg·yr. Through a detailed energy-response model, background characterization, and a binned Poisson likelihood, no significant $0\nu\beta\beta$ signal is observed, yielding a lower limit of $T^{0\nu\beta\beta}_{1/2}>2.1\times10^{24}$ yr and an effective Majorana mass upper range $\langle m_{\beta\beta}\rangle=(0.4-1.6)$ eV/$c^2$. The result surpasses previous natural xenon limits and demonstrates the power of PandaX-4T's background control and energy calibration in the MeV regime, with future upgrades (PandaX-4T and PandaX-xT) expected to probe the inverted neutrino mass ordering with much greater sensitivity. The analysis confirms the viability of large-scale natural xenon detectors for $0\nu\beta\beta$ searches and sets the stage for even more sensitive trials in upcoming xenon-based experiments.

Abstract

We report the search for neutrinoless double-beta decay of $^{136}$Xe from the PandaX-4T experiment with a 3.7-tonne natural xenon target. The data reconstruction and the background modeling are optimized in the MeV energy region. A blind analysis is performed with data from the commissioning run and the first science run. No significant excess of signal over the background is observed. A lower limit on the half-life of $^{136}$Xe neutrinoless double-beta decay is established to be $2.1 \times 10^{24}$~yr at the 90\% confidence level, with a $^{136}$Xe exposure of 44.6~kg$\cdot$year. Our result represents the most stringent constraint from a natural xenon detector to date.

Searching for Neutrinoless Double-Beta Decay of $^{136}$Xe with PandaX-4T

TL;DR

This work reports a blind search for neutrinoless double-beta decay in Xe with the PandaX-4T detector, using a unified MeV-region analysis on Run0 and Run1 data corresponding to a combined exposure of 44.6 kg·yr. Through a detailed energy-response model, background characterization, and a binned Poisson likelihood, no significant signal is observed, yielding a lower limit of yr and an effective Majorana mass upper range eV/. The result surpasses previous natural xenon limits and demonstrates the power of PandaX-4T's background control and energy calibration in the MeV regime, with future upgrades (PandaX-4T and PandaX-xT) expected to probe the inverted neutrino mass ordering with much greater sensitivity. The analysis confirms the viability of large-scale natural xenon detectors for searches and sets the stage for even more sensitive trials in upcoming xenon-based experiments.

Abstract

We report the search for neutrinoless double-beta decay of Xe from the PandaX-4T experiment with a 3.7-tonne natural xenon target. The data reconstruction and the background modeling are optimized in the MeV energy region. A blind analysis is performed with data from the commissioning run and the first science run. No significant excess of signal over the background is observed. A lower limit on the half-life of Xe neutrinoless double-beta decay is established to be ~yr at the 90\% confidence level, with a Xe exposure of 44.6~kgyear. Our result represents the most stringent constraint from a natural xenon detector to date.

Paper Structure

This paper contains 8 sections, 4 equations, 5 figures, 2 tables.

Table of Contents

  1. Introduction
  2. PandaX-4T Detector
  3. Data Reconstruction and Event Selection
  4. Signal and Background Models
  5. Fitting Method and Results
  6. Summary
  7. Acknowledgment
  8. Unblinded fit results in four regions of FV.

Figures (5)

  • Figure 1: Distribution of the positions of reconstructed physics events. The solid red lines represent the boundary of the optimized FV for both Run0 and Run1, with dashed orange lines dividing the FV into 4 regions. The dashed white lines define the outer region, in which the detector response is modeled.
  • Figure 2: Comparison of SS fractions between simulation and data of $^{232}$Th calibration for Run0 (top) and Run1 (bottom) with relative differences between mean values shown in the lower panels. The spectrum-averaged deviations in absolute values are conservatively taken as relative uncertainties for the SS fractions, which are 13% for Run0 and 8% for Run1.
  • Figure 3: Unblinded fit results for Run0 (top) and Run1 (bottom). The contributions from $^{60}$Co, $^{40}$K, $^{232}$Th, and $^{238}$U of different detector parts are combined respectively after fitting for better visualization. $^{136}$Xe $0\nu\beta\beta$ signals are indicated by red-shaded peaks. The lower panel shows the residuals together with the $\pm$1$\sigma$ ($\pm$3$\sigma$) region represented by the dark (light) green band.
  • Figure 4: Pulls of nuisance parameters in the unit of $\sigma$ for blinded fits (yellow bar) and unblinded fits (blue bar). The nuisance parameters of $^{136}$Xe mass only appear in the unblinded fits. The dark (light) green band represents the $\pm1\sigma$ ($\pm2\sigma$) region. All pulls fall within the $\pm2\sigma$ region, and no significant discrepancy arises between blinded and unblinded fit.
  • Figure A: Unblinded fit results in the four regions of FV as indicated in Fig.\ref{['fig:FV']}. The results of the same region for Run0 and Run1 are combined after fitting for better visualization.