The Nab Experiment: An ultraprecise measurement of the electron-antineutrino angular correlation coefficient in neutron beta decay

Nab 实验：中子 β 衰变中电子-反中微子角相关系数的超精确测量

• 批准号: SAPPJ-2019-00043
• 负责人: Mammei, Russell
• 金额: $ 3.64万
• 依托单位: University of Winnipeg
• 依托单位国家: 加拿大
• 项目类别: Subatomic Physics Envelope - Project
• 财政年份: 2020
• 资助国家: 加拿大
• 起止时间: 2020-01-01 至 2021-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=718945
• 关键词: Nab; Experiment; ultraprecise; measurement; electron

The Nab collaboration aims to make the world's most precise measurement of the electron-neutrino angular correlation parameter "a" and the Fierz interference term "b" in cold neutron beta decay. The experiment employs a novel 4 Pi field expansion spectrometer and is located at the Fundamental Neutron Physics Beam line (FNPB) of the Spallation Neutron Source (SNS) at Oak Ridge National Lab in the USA. The Nab collaboration has recently passed several significant milestones with the delivery and installation of the 4 m long superconducting spectrometer magnet on the FNPB and the delivery of several highly segmented Si detectors. The collaboration is anticipating commissioning of the full experiment at the SNS in the spring/summer of 2019, with physics data to begin shortly after for the next 2 years. The measurement of angular correlations in neutron beta-decay provides the most sensitive means to evaluate the ratio of axial to vector coupling constants (Lambda (L) = gA/gV). The precise value of "L" is very important in many applications of the theory of weak interactions, especially in astrophysics, e.g. a star's neutrino production is closely related to L2. Parameter "a'' offers an independent measure of "L'' with comparable sensitivity and radically different systematics than measurements using the correlation parameter “A”, which currently provides the best precision on “L”. The main components of the Nab experiment include a superconducting spectrometer, a set of highly segmented silicon (Si) detectors, and cold neutron beam monitors. The function of the spectrometer is to measure the magnitude of the proton momentum via time of flight (TOF) measurements. It is crucial that the proton silicon detector(s) be fully characterized with a known source of protons before installation into the Nab spectrometer. To that end, a test facility has been developed at the University of Manitoba to characterize the detectors for 30 keV protons. Much of the work over the past three years has focused on getting this facility ready, which includes determining the appropriate beam steering settings using an large area phosphor screen detector to image the beam as well as the building of a large area micro-channel plate (MCP) detector and its associated electronics to act as a reference detector for the silicon detector. The facility will begin characterizing the silicon detector(s) in the winter/spring of 2018-19. Since 2016, one PhD. student and three undergraduate students have received world class training in detector manufacturing/testing while working to build this facility. Given the expanded scope of the project in the coming three years, we anticipate providing additional training to one PhD and one MSc. student and anticipate an increase over previous years travel budget to assist in the commissioning, physics data taking, and analysis of the Nab experiment. Thus our projected budget request is $140k, $141k, $121k over the next three years.

NAB协作旨在使世界上最精确的电子 - 中性角相关参数“ A”和FIFEZ干扰术语“ B”在冷中子β衰减中。该实验采用了一种新型的4 PI场扩展光谱仪，位于美国Oak Ridge National Lab的散布中子源（SNS）的基本中子物理束系（FNPB）。 NAB协作最近通过了几个重要的里程碑，在FNPB上提供了4 m长的超导光谱仪磁铁，并提供了几个高度分割的SI检测器。这项合作预计将在2019年春季/夏季在SNS进行完整实验，并在接下来的两年内开始进行物理数据。 中子β-Decay中角相关性的测量提供了评估轴向与矢量偶联常数（LAMBDA（L）= GA/GV）比率的最敏感手段。在弱相互作用理论的许多应用中，尤其是在天体物理学中，例如恒星的神经元的产生与L2密切相关。参数“ a”提供了与使用相关参数“ A”的测量值相当灵敏度和根本不同的系统的独立度量，该测量当前在“ L”上提供了最佳精度。 NAB实验的主要组件包括超导光谱仪，一组高度分段的硅（SI）探测器和冷中子束监测器。光谱仪的功能是通过飞行时间（TOF）测量值测量质子动量的大小。至关重要的是，在安装到NAB光谱仪中之前，将质子硅检测器（S）充分表征已知的质子来源。为此，曼尼托巴大学已经开发了一个测试设施，以表征30个KEV质子的探测器。在过去三年中，许多工作都集中在准备好此设施上，其中包括使用大面积磷光器屏幕探测器确定适当的梁转向设置，以对梁进行成像以及建造大面积微通道板（MCP）探测器及其相关的电子设备，以充当硅探测器的参考探测器。该设施将在2018 - 19年冬季/春季开始表征硅探测器。自2016年以来，一家博士学位。学生和三名本科生在努力建造此设施的同时，已经接受了探测器制造/测试的世界一流培训。鉴于该项目在未来三年内的扩大范围，我们预计将为一位博士和一项MSC提供额外的培训。学生并预计往年的旅行预算有所增加，以帮助NAB实验进行调试，物理数据获取和分析。我们预计的预算要求为$ 140K，14.1万美元，在未来三年内$ 121K。