超级神冈中的天体背景是由μ子诱发的阵雨形成的
Spallation Backgrounds in Super-Kamiokande Are Made in Muon-Induced Showers
摘要：
关于太阳和超新星中微子的关键问题仍然没有答案。Super-Kamiokande具有进步所需的曝光，但探测器背景是一个限制因素。宇宙射线μ子产生的同位素的β衰变和它们的二次衰变是一个主要的组成部分，它们会引发核裂变反应。在μ子径迹之后和周围的事件的切割使这种溅射衰变本底减少了$\simeq 90\%$（以$\simeq 20\%$死时间为代价），但它在6- 18 MeV的速率仍然占主导地位。在Super-Kamiokande论文[Bays { \it et al.}，物理学~修订版~ D { \bf 85}，052007（2012）]对弥散超新星中微子背景的搜索。他们发现，在16 MeV以上的spectrometry衰变之前，在同一位置附近，μ子的切伦科夫光剖面中出现了一个峰值;对μ子轨道的有限部分进行了更积极的切割，导致背景减少而没有增加死区时间。我们把他们的经验发现建立在坚实的理论基础上。我们表明，几乎所有的spiral衰变同位素产生的μ子诱导的阵雨，这些阵雨是罕见的，足够的能量是可识别的。这是第一次对任何探测器进行这样的演示。我们详细介绍了如何物理学的阵雨解释峰的μ子切伦科夫光剖面和其他超K观测。我们的研究结果提供了一个物理基础，实际改善背景拒绝，将有利于多个研究。特别是对于太阳中微子来说，在能量低至6 MeV的情况下，应该可以大大减少背景。
英文摘要：
Crucial questions about solar and supernova neutrinos remain unanswered. Super-Kamiokande has the exposure needed for progress, but detector backgrounds are a limiting factor. A leading component is the beta decays of isotopes produced by cosmic-ray muons and their secondaries, which initiate nuclear spallation reactions. Cuts of events after and surrounding muon tracks reduce this spallation decay background by $\simeq 90\%$ (at a cost of $\simeq 20\%$ deadtime), but its rate at 6--18 MeV is still dominant. A better way to cut this background was suggested in a Super-Kamiokande paper [Bays {\it et al.}, Phys.~Rev.~D {\bf 85}, 052007 (2012)] on a search for the diffuse supernova neutrino background. They found that spallation decays above 16 MeV were preceded near the same location by a peak in the apparent Cherenkov light profile from the muon; a more aggressive cut was applied to a limited section of the muon track, leading to decreased background without increased deadtime. We put their empirical discovery on a firm theoretical foundation. We show that almost all spallation decay isotopes are produced by muon-induced showers and that these showers are rare enough and energetic enough to be identifiable. This is the first such demonstration for any detector. We detail how the physics of showers explains the peak in the muon Cherenkov light profile and other Super-K observations. Our results provide a physical basis for practical improvements in background rejection that will benefit multiple studies. For solar neutrinos, in particular, it should be possible to dramatically reduce backgrounds at energies as low as 6 MeV.
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