Low Energy Nuclear Physics at Princeton - The Borexino Solar Neutrino Experiment

Borexino是一个新的太阳中微子实验，它将使用300吨高纯度液体闪烁体来测量太阳中微子谱的低能部分（E1 MeV）。 30多年的实验表明，从核聚变反应中探测到的太阳中微子比预期的要少。 最近的实验表明，这种差异是由于“中微子振荡”，即太阳中产生的中微子作为“电子中微子”振荡到非电子中微子状态的过程。 如果中微子确实有一个有限的质量，而不是像现在的基本粒子标准模型那样质量为零，那么振荡过程是可能的。 如果振荡被证实，中微子也有质量，那么这一结果将大大偏离我们目前对基本粒子的理解，并在物理学和天文学上产生重要影响。萨德伯里中微子天文台的最新实验数据以及SuperK实验为中微子振荡提供了最有说服力的证据。 在Mikheyev-Smirnov-Wolfenstein理论框架中对这些和其他数据的解释表明，低于1 MeV的中微子的振荡效应可能是戏剧性的。 一个观测的可能性是低能量中微子的计数率有很大的昼夜不对称性。 Borexino被设计用于测量0.86MeV的7 Be中微子，因此很好地定位于探索这种独特的低能中微子振荡效应。Borexino探测器位于意大利的Gran Sasso地下实验室。 探测7 Be中微子所需的低本底条件带来了巨大的技术挑战。 经过几年的原型探测器研发和四年的建设，Borexino预计将于2002年投入使用。 在2002-2004两年期间，这项建议的目标是完成Borexino和收集太阳中微子数据的卫星的试运行和启动阶段。 该提案将支持伊顿大学集团完成和操作μ子探测器和闪烁体净化，填充和探测器的安全壳子系统。 它还将支持数据采集和数据分析的早期阶段。

Borexino is a new solar neutrino experiment that will use 300 tons ofhigh purity liquid scintillator to measure the low energy part of thesolar neutrino spectrum (E 1MeV). More than 30 years of experimentshave shown that fewer solar neutrinos are detected than expected fromthe nuclear fusion reactions that power the sun. Recent experimentsindicate that the discrepancy is due to "neutrino oscillations", aprocess in which neutrinos produced in the sun as "electron-neutrinos",oscillate to a non-electron-neutrino state. The oscillation process ispossible if neutrinos do indeed have a finite mass, rather than a zeromass, as is the case in the present standard model of elementaryparticles. If oscillations are confirmed, and neutrinos have mass, theresult would be a major departure from our current understanding ofelementary particle, with important implications in physics andastronomy. The latest experimental data of the Sudbury Neutrino Observatory,together with the SuperK experiment, provide the most convincingevidence that neutrinos are oscillating. The interpretation of theseand other data in the Mikheyev-Smirnov-Wolfenstein theoretical frameworkindicates that oscillation effects for neutrinos below 1 MeV could bedramatic. One observational possibility is a large day/night asymmetryin count rate for low energy neutrinos. Borexino is designed to measurethe 0.86 MeV 7Be neutrinos and is thus well positioned to explore thisunique low energy neutrino oscillation effect. The Borexino detector is located in the Gran Sasso undergroundlaboratory in Italy. The low background requirements necessary fordetecting 7Be neutrinos pose formidable technical challenges. Afterseveral years of R&D with a prototype detector, and four years ofconstruction, Borexino is expected to become operational in 2002. Theobjective of this proposal in the two-year period 2002-2004 is tocomplete the commissioning and start-up phase of Borexino and begintaking solar neutrino data. This proposal will support the PrincetonUniversity Group in completing and operating the muon detector and thescintillator purification, filling, and containment subsystems of thedetector. It will also support the early stages of data acquisition anddata analysis.