Borexino Solar Neutrino Experiment

Borexino太阳中微子实验

• 批准号: 0503816
• 负责人: Frank Calaprice
• 金额: $ 321万
• 依托单位: Princeton University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2005
• 资助国家: 美国
• 起止时间: 2005-06-01 至 2009-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0503816&HistoricalAwards=false
• 关键词: Borexino; Solar; Neutrino; Experiment

Summary of the Borexino Solar Neutrino ExperimentBorexino is a large scintillation detector designed to observe low energy neutrinos produced by the Sun. It will contain 300 tons of liquid scintillator made of materials chosen for their low content of radioactive atoms and is located in the underground Gran Sasso laboratory in Italy. Measurements to be performed will test our understanding of how the Sun produces energy and our understanding of neutrinos. The Sun is thought to derive its energy from a series of nuclear fusion reactions that convert four hydrogen nuclei into a helium nucleus, with the release of a large amount of energy (26.7 MeV). The reactions occur in the dense hot core of the sun and the energy is transferred to charged particles, gamma rays, and neutrinos. However, only the neutrinos escape into space as messengers from the hot core.The chlorine detector of Ray Davis and colleagues was the first experiment designed for solar neutrinos as a test of the solar model. Surprisingly, it recorded only about 1/3 of the neutrinos predicted. Doubts about the experiment and the solar model, on which the expected neutrino rate is based, persisted. However, after several measurements with new detectors, it became clear that both the Davis experiment and the calculated neutrino rates were correct. More recently, the Sudbury Neutrino Observatory in Canada, using heavy water, demonstrated beyond doubt that the deficit of detected solar neutrinos was due to a fundamentally new process known as "neutrino oscillations". The neutrinos are produced in the sun as "electron-neutrinos", one of the three known neutrino states, and then oscillate to other neutrino states in their journey from the Sun to Earth. Since solar neutrino experiments detect mainly electron neutrinos, the observed rates were always smaller than expected. A process proposed by Mikheyev, Smirnov and Wolfenstein (MSF effect) would enhance oscillations by the interaction of the neutrinos with electrons in the solar core. What will Borexino contribute to the story? The first goal is to test the MSW theory. A transition in the nature of neutrino oscillations is expected to occur at a neutrino energy of approximately 2 MeV. Above the transition energy, neutrino oscillations are dominated by MSW oscillations, whereas below that energy, the matter effect is small and neutrinos should oscillate by "vacuum oscillations". Borexino will be the first experiment to directly detect neutrinos below the transition energy. The goal is to measure the rate of the 0.86 MeV 7Be neutrino and the 1.44 MeV pep neutrino, for which vacuum oscillations should dominate. The SNO and SuperK experiments detected high energy neutrinos, where MSW oscillations dominate. A significant change in the survival probability of the neutrinos above and below the transition energy should provide a unique test the MSW picture. A second goal of Borexino is to test whether all the energy produced by the Sun arises from the fusion reactions. This can be done by measuring the neutrino rates from all the nuclear reactions that occur in the Sun. From the observed neutrino rates, corrected for neutrino oscillations, one determines the total power produced by the Sun from nuclear reactions. This total power is then compared to the power determined from the radiant power, the photon luminosity. A difference would imply another source of energy, or possibly a non-equilibrium condition. Borexino also has applications beyond nuclear physics and astronomy. It is an ideal detector of geophysical anti-neutrinos (produced by natural radioactivity in the earth), and supernova neutrinos. Borexino will additionally provide a sensitive search for so-called sterile neutrinos and non-standard neutrino interactions. The detector was built with prior funding from the NSF and with funds from European science agencies. The goal of this proposal is to bring the detector into full operation within the next two years and to start data acquisition; significant parts of this effort will involve graduate students and postdoctoral research associates, in addition to the faculty members involved.

Borexino是一个大型闪烁探测器，设计用于观测太阳产生的低能中微子。 它将包含300吨由放射性原子含量低的材料制成的液体闪烁体，并位于意大利的地下Gran Sasso实验室。 将要进行的测量将测试我们对太阳如何产生能量的理解以及我们对中微子的理解。 太阳被认为是从一系列核聚变反应中获得能量，这些反应将四个氢核转化为一个氦核，并释放出大量能量（26.7 MeV）。 这些反应发生在太阳致密的热核中，能量被转移到带电粒子、伽马射线和中微子中。 然而，只有中微子作为信使从热核逃逸到太空中。雷·戴维斯和同事的氯探测器是第一个为太阳中微子设计的实验，作为对太阳模型的测试。 令人惊讶的是，它只记录了预测的中微子的1/3。 对实验和太阳模型的怀疑仍然存在，而太阳模型是预期中微子速率的基础。 然而，在用新的探测器进行了几次测量之后，戴维斯实验和计算出的中微子速率都是正确的。最近，加拿大的萨德伯里中微子天文台使用重水，毫无疑问地证明了探测到的太阳中微子的不足是由于一种被称为“中微子振荡”的全新过程。 中微子在太阳中以“电子中微子”的形式产生，这是三种已知的中微子状态之一，然后在从太阳到地球的旅程中振荡到其他中微子状态。 由于太阳中微子实验主要检测电子中微子，因此观测到的速率总是小于预期。 米赫耶夫、斯米尔诺夫和沃尔芬斯坦提出的一个过程（MSF效应）将通过中微子与太阳核心电子的相互作用来增强振荡。Borexino将为这个故事做出什么贡献？ 第一个目标是测试MSW理论。 中微子振荡性质的转变预计将在中微子能量约为2 MeV时发生。 在跃迁能量以上，中微子振荡主要是MSW振荡，而在跃迁能量以下，物质效应很小，中微子应该是“真空振荡”。 Borexino将是第一个直接探测跃迁能量以下中微子的实验。 目标是测量0.86 MeV 7 Be中微子和1.44 MeV pep中微子的速率，真空振荡应该占主导地位。 SNO和SuperK实验探测到了高能中微子，其中MSW振荡占主导地位。 中微子在跃迁能量以上和以下的生存概率的显着变化应该提供一个独特的测试MSW图片。Borexino的第二个目标是测试太阳产生的所有能量是否都来自聚变反应。 这可以通过测量太阳中发生的所有核反应的中微子速率来实现。 从观测到的中微子速率，修正了中微子振荡，人们确定了太阳从核反应中产生的总功率。 然后将这个总功率与由辐射功率确定的功率（光子光度）进行比较。 差异意味着另一种能量来源，或者可能是非平衡状态。 Borexino还具有核物理和天文学以外的应用。 它是地球物理反中微子（由地球中的天然放射性产生）和超新星中微子的理想探测器。 Borexino还将为所谓的无菌中微子和非标准中微子相互作用提供灵敏的搜索。 该探测器是在NSF和欧洲科学机构的资助下建造的。 该提案的目标是在未来两年内使探测器全面投入运行并开始数据采集;这项工作的重要部分将涉及研究生和博士后研究助理，以及相关的教职员工。