升级后的CJPL-I 1吨水切伦科夫原型探测器的μ子探测与方向重建
Muon Detection and Direction Reconstruction with the Upgraded 1-ton Water Cherenkov Prototype Detector at CJPL-I
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- Tsinghua University（清华大学）
- Lanzhou University（兰州大学）
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中文总结 AI 辅助
该研究升级了锦屏中微子实验的1吨水切伦科夫原型探测器，采用60个MCP-PMT，测得μ子通量为(3.55±0.43±0.28)×10⁻¹⁰ cm⁻²s⁻¹，方向重建精度提升至6°，并识别出罕见上行μ子事件。
中文摘要 AI 辅助
用于锦屏中微子实验的1吨原型探测器（JNE-1ton）已完成硬件升级，并在位于2400米岩石覆盖层下的CJPL-I成功以水和液体闪烁体两种模式运行。升级期间，探测器的机械支撑结构和光电倍增管布局被重新设计。原有的滨松PMT被替换为来自北方夜视的8英寸MCP-PMT，PMT数量从30个增加到60个。随后，探测器以水模式运行了85天（Water-I）和79天（Water-II）。根据积累的水模式数据，我们得出μ子探测效率（Water-II）比升级前的液体闪烁体探测器高出约59%。测得的μ子通量为$\phi_{\text{I+II}} = (3.55 \pm 0.43_{\mathrm{stat}}\pm 0.28_{\mathrm{syst}}) \times 10^{-10}~\mathrm{cm}^{-2}\mathrm{s}^{-1}$，与之前的测量结果一致。由于切伦科夫辐射的特征角度依赖性以及增加的PMT覆盖范围，μ子方向重建的不确定性约为6$^\circ$，相当于降低到之前值的30%。值得注意的是，清楚识别出一个罕见的上行μ子事件。它被排除在宇宙射线μ子通量样本之外，并为中国最深地下实验室中的中微子诱导事件研究打开了新窗口。这项工作标志着CJPL首次采用经济高效的水探测器进行μ子通量测量。
英文摘要
The 1-ton prototype detector for Jinping neutrino experiment (JNE-1ton) has completed its hardware upgrade and has been successfully operated in both water and liquid-scintillator modes at CJPL-I, which is situated under a 2400-m rock overburden. During the upgrade, the detector's mechanical support structure and PMT layout were redesigned. The original Hamamatsu PMTs were replaced with 8-inch MCP-PMTs from North Night Vision, increasing the PMT count from 30 to 60. The detector was then operated in water mode for 85 days (Water-I) and 79 days (Water-II). From the accumulated water-mode data, we derive a muon detection efficiency (Water-II) that is approximately 59% higher than that of the pre-upgrade liquid scintillator detector. The measured muon flux is $ϕ_{\text{I+II}} = (3.55 \pm 0.43_{\mathrm{stat}}\pm 0.28_{\mathrm{syst}}) \times 10^{-10}~\mathrm{cm}^{-2}\mathrm{s}^{-1}$, which is consistent with the previous measurement. Owing to the characteristic angular dependence of Cherenkov radiation and the increased PMT coverage, the uncertainty in muon direction reconstruction is approximately 6$^\circ$, which corresponds to a reduction to 30% of its previous value. Notably, one rare up-going muon event was clearly identified. It is excluded from the cosmic-ray muon flux sample and opens a new window for neutrino-induced event studies in the deepest underground laboratory in China. This work marks the first time that CJPL has employed a cost-effective water detector for muon flux measurement.
