Borexino Solar Neutrino Experiment

项目编号：0802646INSTUTION：普林斯顿大学NSF计划：PHY粒子ASTROPHYSICSPRINCIPAL调查员：Calaprice，Frank P.TITLE：Borexino太阳中微子实验Borexino是一个大型地下液体闪烁探测器，旨在观测由太阳产生的低能中微子，以阐明太阳如何产生能量，并更好地了解中微子的基本性质。该探测器自2007年5月投入使用，包含300吨超纯液体闪烁体，位于意大利Gran Sasso地下实验室。到目前为止，质子-质子(PP)循环是太阳中占主导地位的一组核聚变反应-S致密、热的核心，将四个氢原子转化为一个氦原子，每个循环产生26.7兆电子伏特的能量。能量被释放为带电粒子、伽马射线和中微子。带电粒子和伽马射线通过碰撞过程将能量传递给其他原子。能量慢慢地扩散到太阳表面，在那里主要以可见光的形式辐射到太空中。另一方面，中微子与物质的相互作用很弱。它们几乎不受干扰地走出太阳，提供了对其核心的直接观察。90%的中微子(所谓的pp中微子)是在pp循环的第一步产生的；其余的大部分是在涉及同位素7Be的循环的后一步产生的。中微子的质量很小，可以让电子型中微子在太阳和地球之间振荡，进入更难探测到的状态。中微子振荡解释了所有的数据，假设人们还考虑到它们与太阳中物质的弱相互作用？Mikheyev、Smirnov和Wolfenstein(MSW)所描述的物质增强振荡。Borexino探测器已经获得了第一组数据，到目前为止，这些数据与MSW对7Be中微子的预测一致。该奖项将为普林斯顿大学继续参与Borexino项目提供资金。闪烁体系统和净化工厂都是普林斯顿大学的责任，需要持续维护，他们打算重新净化闪烁体，以在探测器中实现更低的背景，进一步提高中微子信号的清晰度。Borexino项目将继续为研究生和本科生提供一个极好的机会，培训他们在电子、化学、放射学、材料科学、软件开发，当然还有基础物理方面的应用。在过去的四年里，普林斯顿的Borexino项目一直活跃在一个外展项目中，该项目将来自意大利相对贫困地区的高中生吸引到普林斯顿参加一个物理暑期项目。在建造和安装探测器过程中开发的技术包括新的低本底技术和开发减少空气中氡的系统。两者都有潜在的商业或政府用途，例如，在安全应用中。

PROPOSAL NUMBER: 0802646INSTITUTION: Princeton UniversityNSF PROGRAM: PHY - PARTICLE ASTROPHYSICSPRINCIPAL INVESTIGATOR: Calaprice, Frank P.TITLE: Borexino Solar Neutrino Experiment ABSTRACTBorexino is a large underground liquid scintillation detector designed to observe low-energy neutrinos, subatomic particles produced by the sun, to elucidate how the sun produces energy and to better understand the fundamental properties of neutrinos. The detector, in operation since May 2007, contains 300 tons of ultra-pure liquid scintillator and is located in the underground Gran Sasso laboratory in Italy. The proton-proton (pp) cycle, by far the dominant set of nuclear fusion reactions in the sun?s dense, hot core, converts four hydrogen atoms into a helium atom and produces 26.7 MeV of energy per cycle. The energy is released to charged particles, gamma rays, and neutrinos. The charged particles and gamma rays transfer energy by collision processes to other atoms. Energy slowly diffuses to the solar surface, where it is radiated into space mainly as visible light. Neutrinos, on the other hand, interact only weakly with matter. They travel almost unperturbed out of the sun, providing a direct view into its core. Ninety percent (the so-called pp neutrinos) are generated in the first step of the pp cycle; most of the rest are produced in a later step of the cycle involving the isotope 7Be. Neutrinos have a small mass that allows the electron-type neutrinos to oscillate, between sun and Earth, into states that are more difficult to detect. Neutrino oscillations explain all the data, provided one also considers their weak interactions with the matter in the sun ? the matter-enhanced oscillations described by Mikheyev, Smirnov, and Wolfenstein (MSW). The Borexino detector has already acquired a first set of data that so far agrees with MSW predictions for 7Be neutrinos. This award will provide funding for Princeton University to continue to participate in the Borexino project. The scintillator system and the purification plants, both Princeton responsibilities, require ongoing maintenance and they intend to re-purify the scintillator to achieve still lower backgrounds in the detector, further enhancing clarity of the neutrino signals. The Borexino project will continue to provide an excellent opportunity for training graduate and undergraduate students in applications of electronics, chemistry, radiology, materials science, software development, and of course fundamental physics. For the past four years the Borexino project at Princeton has been active in an outreach program that brings high school students from a relatively poor region of Italy to Princeton for a summer program in physics. Technology developed in the process of detector construction and installation includes new low-background techniques and development of a system for the reduction of radon in air. Both have potential commercial or governmental use, e.g., in security applications.