Borexino Solar Neutrino Experiment

提案编号：0802646研究机构：普林斯顿大学国家科学基金会（NSF）物理学-粒子天体物理学闪烁探测器：Calaprice，Frank P.标题：Borexino太阳中微子实验摘要Borexino是一个大型的地下液体闪烁探测器，旨在观察太阳产生的低能中微子，亚原子粒子，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。该探测器于2007年5月投入运行，装有300吨超纯液体闪烁体，位于意大利的Gran Sasso地下实验室。质子-质子（pp）循环是目前太阳核聚变反应中最主要的一种？它的致密、炽热的核心将四个氢原子转化为一个氦原子，每一个周期产生26.7兆电子伏的能量。能量释放到带电粒子、伽马射线和中微子中。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，在那里它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离开太阳，提供了一个直接进入太阳核心的视角。其中90%（即所谓的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7 Be的循环的后期产生的。中微子的质量很小，这使得电子型中微子能够在太阳和地球之间振荡，进入更难以检测的状态。中微子振荡解释了所有的数据，如果人们也考虑到它们与太阳中物质的弱相互作用？米赫耶夫、斯米尔诺夫和沃尔芬斯坦所描述的物质增强振荡（MSW）。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7 Be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。闪烁体系统和纯化工厂都需要普林斯顿大学的责任，需要持续的维护，他们打算重新纯化闪烁体，以实现更低的背景探测器，进一步提高中微子信号的清晰度。Borexino项目将继续为培养研究生和本科生在电子，化学，放射学，材料科学，软件开发，当然还有基础物理学应用方面提供极好的机会。在过去的四年里，普林斯顿大学的Borexino项目一直活跃在一个推广项目中，该项目将意大利一个相对贫困地区的高中生带到普林斯顿大学参加一个物理学暑期项目。在探测器建造和安装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.