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

普林斯顿大学的低能核物理 - Borexino 太阳中微子实验

• 批准号: 0077423
• 负责人: Frank Calaprice
• 金额: $ 210万
• 依托单位: Princeton University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2000
• 资助国家: 美国
• 起止时间: 2000-06-15 至 2002-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0077423&HistoricalAwards=false
• 关键词: Low; Energy; Nuclear; Physics; Princeton

0077423CalapriceIn 1938, Hans Bethe provided the first explanation of the energy production inside the Sun that was able to account for the energy flux we have observed over the lifetime of the Earth. This theory is based on thermonuclear reaction processes occurring in the Sun's core. In Bethe's seminal work, two energy production mechanisms were discussed: the so-called carbon-nitrogen-oxygen (CNO) and the proton-proton (pp) cycles. Today, it is the latter process that is thought to be responsible for the production of more than 98% of the energy flowing from the Sun. The pp cycle consists of a series of nuclear reactions that convert four hydrogen atoms to a helium atom, releasing an energy of 26.7 Mev for each conversion. The energy is released in the form of charged particle kinetic energies, gamma rays, and neutrinos. Because of their weak interaction, the neutrinos leave the sun with very few interactions.The "solar neutrino problem" came in existence more than 35 years ago, when the pioneering "Chlorine" experiment of Ray Davis and collaborators showed that the actual number of neutrinos measured on Earth was only about 1/3 of the number predicted by the "standard solar model". Since then, other experiments have been performed and all find a deficit of observed neutrinos, compared to the prediction. The present body of experimental evidence indicates that the deficit is not due to a flaw in our understanding of the Sun, but rather, is caused by fundamental neutrino processes that convert the normal electron-type neutrinos produced in the sun to neutrinos not readily detected in the current detectors. The neutrino conversions or "neutrino oscillations" can occur if the neutrino has a non-zero mass. But a non-zero neutrino mass is contrary to standard particle physics theory. Thus, the "solar neutrino problem" has become an issue of fundamental importance to elementary particle physics. If the neutrino does have mass, as suggested by the current experiments, new fundamental physics theories will be required.Borexino is a new solar neutrino detector designed to detect low energy solar neutrinos by use of a large 300 ton liquid scintillator. The detector will be located in the Gran Sasso underground laboratory in Italy. It's principle objective is to detect the mono-energetic Be-7 neutrino at an energy of 0.86 MeV. According to current analysis of solar neutrino data, the Be-7 neutrino is expected to exhibit maximal neutrino oscillation effects. Borexino will attempt to observe direct evidence of neutrino oscillations and confirm the present hypothesis of neutrino mass. The signals to be searched for include very large annual and day/night variations in count rate that are uniquely caused by neutrino oscillations.

0077423Calapricein，1938年，汉斯·伯特（Hans Bethe）对太阳内的能源产量提供了第一个解释，该解释能够解释我们在地球一生中观察到的能量通量。 该理论基于太阳核心发生的热核反应过程。 在伯特（Bethe）的开创性工作中，讨论了两种能源生产机制：所谓的碳氮 - 氧（CNO）和质子 - 蛋白质（PP）周期。 如今，正是后一个过程被认为是造成超过98％从太阳流动的能量的98％以上的原因。 PP循环由一系列核反应组成，这些反应将四个氢原子转换为氦原子，每次转化释放了26.7 MeV的能量。 能量以带电粒子动能，伽马射线和中微子的形式释放。 由于中微子的相互作用较弱，中微子以很少的相互作用离开了太阳。35年前，“太阳中微子问题”存在，当时雷·戴维斯（Ray Davis）的开创性“氯”实验和合作者表明，在地球上测得的中微子数量仅为地球上的中微子数量约为1/3的数量。 从那时起，与预测相比，已经进行了其他实验，并且都发现观察到的中微子的缺陷。 目前的实验证据表明，赤字并不是由于我们对太阳的理解中存在缺陷，而是由基本中微子过程引起的，这些中微子过程转化了在太阳下产生的正常电子中微子，以在当前检测器中不容易检测到中微子。 如果中微子的质量非零，则可能发生中微子转化或“中微子振荡”。 但是非零的中微子质量与标准粒子物理理论背道而驰。 因此，“太阳中微子问题”已成为对基本粒子物理学的根本重要性的问题。 如当前实验所建议的那样，如果中微子确实具有质量，则需要新的基本物理学理论。Borexino是一种新的太阳中微子检测器，旨在通过使用大型300吨液体scintillator来检测低能太阳中微子。 该探测器将位于意大利的Gran Sasso地下实验室中。 它的主要目的是以0.86 meV的能量检测单能BE-7中微子。 根据目前对太阳中微子数据的分析，预计BE-7中微子将表现出最大的中微子振荡效应。 Borexino将尝试观察中微子振荡的直接证据，并确认中微子质量的当前假设。 要搜索的信号包括由中微子振荡引起的计数率的年度和白天/夜间变化。