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arXiv 2410.04048hep-ex
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MicroBooNE 关于 MiniBooNE 低能超出的光子解释的研究

MicroBooNE investigations on the photon interpretation of the MiniBooNE low energy excess

Guanqun Ge

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PhD thesis
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AI总结：

MicroBooNE实验利用前三年数据，通过提升决策树等方法搜寻两种中性流单光子过程，检验MiniBooNE低能超出的光子解释，给出了相关过程的实验上限。

摘要：

MicroBooNE 实验是位于费米实验室的一个有效体积为85吨的液氩时间投影室，于2015年至2020年运行，用于收集费米实验室增强器中微子束（Booster Neutrino Beam）的中微子数据。MicroBooNE 的物理目标之一是探究 MiniBooNE 实验在 ν_μ→ν_e 中微子振荡测量中观测到的低能超出的可能解释。MicroBooNE 已开展多项搜寻工作，以检验针对 MiniBooNE 低能超出的假设性解释，包括光子本底被低估或固有 ν_e 本底的可能性。本论文介绍了 MicroBooNE 对两种中性流（NC）单光子产生过程的搜寻，这两种过程会构成 MiniBooNE 测量的光子本底：一是 NC Δ 共振产生后发生 Δ 辐射衰变，即 Δ→Nγ；二是 NC 相干单光子产生。两项搜寻均利用提升决策树（boosted decision trees）实现高效的本底排除，通过高统计量的 NC π^0 测量来约束主要本底，并使用了 MicroBooNE 前三年的数据。NC Δ→Nγ 测量在90%置信水平（C.L.）下给出了 Δ 辐射衰变过程的上限，为预测标称速率的2.3倍，在94.8%置信水平下排除了 MiniBooNE 低能超出的一种候选光子解释——该解释认为其强度为标称 NC Δ 辐射衰变速率的3.18倍。NC 相干单光子测量得出了世界上首个1 GeV以下该过程截面的实验限制，在90%置信水平下为 1.49×10^-41 cm²，对应标称预测值的24.0倍。

英文摘要：

The MicroBooNE experiment is a liquid argon time projection chamber with 85-ton active volume at Fermilab, operated from 2015 to 2020 to collect neutrino data from Fermilab's Booster Neutrino Beam. One of MicroBooNE's physics goals is to investigate possible explanations of the low-energy excess observed by the MiniBooNE experiment in $ν_μ\rightarrow ν_{e}$ neutrino oscillation measurements. MicroBooNE has performed searches to test hypothetical interpretations of the MiniBooNE low-energy excess, including the underestimation of the photon background or instrinic $ν_{e}$ background. This thesis presents MicroBooNE's searches for two neutral current (NC) single-photon production processes that contribute to the photon background of the MiniBooNE measurement: NC $Δ$ resonance production followed by $Δ$ radiative decay: $Δ\rightarrow Nγ$, and NC coherent single-photon production. Both searches take advantage of boosted decision trees to yield efficient background rejection, and a high-statistic NC $π^0$ measurement to constrain dominant background, and make use of MicroBooNE's first three years of data. The NC $Δ\rightarrow Nγ$ measurement yielded a bound on the $Δ$ radiative decay process at 2.3 times the predicted nominal rate at 90% confidence level (C.L.), disfavoring a candidate photon interpretation of the MiniBooNE low-energy excess as a factor of 3.18 times the nominal NC $Δ$ radiative decay rate at the 94.8% C.L. The NC coherent single photon measurement leads to the world's first experimental limit on the cross-section of this process below 1 GeV, of $1.49 \times 10^{-41} \text{cm}^2$ at 90% C.L., corresponding to 24.0 times the nominal prediction.

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