A search for the neutrinoless quadruple beta decay of ¹³⁶Xe was conducted with the liquid-xenon detector XMASS-I using 327 kg ×800.0 days of the exposure. The pulse shape discrimination based on the scintillation decay time constant which distinguishes γ-rays including the signal and β-rays was used to enhance the search sensitivity. No significant signal excess was observed from the energy spectrum fitting with precise background evaluation, and we set a lower limit of the half life of 3.7 × 10²⁴ years at 90% confidence level. This is the first experimental constraint of the neutrinoless quadruple beta decay of ¹³⁶Xe.

中文翻译：

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在 XMASS-I 中寻找 136Xe 的无中微子四倍 β 衰变

使用液体氙探测器 XMASS-I 进行了¹³⁶ Xe的无中微子四倍β衰变的搜索，曝光时间为 327 kg × 800.0 天。基于闪烁衰减时间常数的脉冲形状鉴别用于区分包括信号的γ射线和β射线，用于提高搜索灵敏度。从具有精确背景评估的能谱拟合中没有观察到显着的信号过量，我们在 90% 的置信水平下设定了 3.7 × 10 ²⁴年的半衰期下限。这是¹³⁶ Xe 的无中微子四倍β衰变的第一个实验约束。