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Collaborative Research: A Search for the Electric Dipole Moment of the Neutron

合作研究：寻找中子的电偶极矩

基本信息

批准号：
1822515
负责人：
Bradley Filippone
金额：
$ 329.12万
依托单位：
California Institute of Technology
依托单位国家：
美国
项目类别：
Continuing Grant
财政年份：
2018
资助国家：
美国
起止时间：
2018-09-15 至 2024-08-31
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=1822515&HistoricalAwards=false
关键词：
Collaborative Research Search Electric Dipole

项目摘要

To search for new laws of nature beyond our current understanding, researchers can use very high energy accelerators, such as the Large Hadron Collider at CERN, or alternatively they can make precise experimental measurements of basic particle properties and search for deviations from the known physical laws. For example, the universe now has much more ordinary matter than anti-matter but no mechanism of known particle interactions can explain how the universe evolved from the matter-antimatter balance at the time of the Big Bang to the present, highly unbalanced, situation. By making precision measurements, it is possible to detect the echoes of early particles and interactions, common at the time of the Big Bang, in quantities like the electric dipole moment of the neutron. That characteristic of neutrons reflects the separation of the neutron's internal positive and negative charges. This award supports design and construction of highly specialized instrumentation that is needed to precisely measure the neutron's electric dipole moment. In addition to advancing our knowledge in sub-atomic physics and cosmology, and generating technological progress, this experiment will involve post-doctoral scholars, graduate and undergraduate students as an essential part, affording the young researchers exceptional opportunities to advance their education and training in a forefront area of nuclear physics. Some technological developments are expected as several SBIR and STTR grants related to the experimental apparatus have been awarded to date.The neutron electric dipole moment (nEDM) is an explicitly time-reversal-violating observable that has played an important role in descriptions of elementary particle physics; measured upper limits continue to limit extensions of prevailing models. Measurements at the scale of 10^-28 e-cm as proposed here will provide important input at combinations of very high mass scales and small mixing angles. The neutron EDM is also important for understanding the general pattern of T-(CP-) violation and the cause of the observed asymmetry of matter and antimatter in the universe. This experiment, to be performed at the Fundamental Neutron Physics Beamline of the Spallation Neutron Source at ORNL, is based on a technique that is qualitatively different from the strategies adopted in previous measurements. The basic technique in the present experiment involves formation of a three-component fluid of polarized neutrons and Helium-3 atoms dissolved in a bath of superfluid Helium-4 at a temperature T ~ 0.5 K. The ultracold neutrons in this volume will be produced by the collision of 8.9 angstrom neutrons with the phonons of the superfluid. The neutron and Helium-3 magnetic dipoles precess in the plane perpendicular to an applied external magnetic field, B0 in a traditional Nuclear Magnetic Resonance arrangement. The nEDM, dn, is determined by measuring the neutron precession frequency in the presence of a strong electric field, E0. Application of the electric field parallel (antiparallel) to B0 changes the Larmor precession frequency, nu, in proportion to dn. With B0 = 30 milliGauss and E0 = 50 kiloVolt/cm, nu = 88 Hertz and the frequency shift is 4.8 nanoHertz for an EDM of 10^-28 e-cm. Operationally, the neutron precession frequency is measured relative to that of the Helium-3 by taking advantage of the strongly spin dependent nuclear capture reaction and detecting the recoiling proton and triton via scintillation produced in the liquid Helium-4. The polarized Helium-3 atoms (in the same volume as the neutrons) also comprise a co-magnetometer (since any EDM of the Helium-3 atoms is suppressed by its atomic electrons); their precession is observed directly using SQUIDS.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

为了寻找超出我们目前理解的新自然定律，研究人员可以使用非常高能量的加速器，例如欧洲核子研究中心的大型强子对撞机，或者他们可以对基本粒子属性进行精确的实验测量并寻找与已知物理定律的偏差。例如，宇宙现在有比反物质更多的普通物质，但没有已知粒子相互作用的机制可以解释宇宙如何从大爆炸时的物质-反物质平衡演变到现在的高度不平衡的情况。通过精确的测量，可以探测到早期粒子和相互作用的回波，在大爆炸时很常见，数量类似于中子的电偶极矩。中子的这种特性反映了中子内部正负电荷的分离。该奖项支持设计和建造精确测量中子电偶极矩所需的高度专业化仪器。除了推进我们在亚原子物理学和宇宙学的知识，并产生技术进步，这个实验将涉及博士后学者，研究生和本科生作为一个重要组成部分，为年轻的研究人员提供特殊的机会，以提高他们的教育和培训在核物理的前沿领域。一些技术的发展，预计随着几个SBIR和STTR赠款有关的实验apparent.The中子电偶极矩（nEDM）是一个明确的时间反演违反观察，在基本粒子物理的描述中发挥了重要作用，测量上限继续限制扩展的流行模型。在这里提出的10^-28 e-cm尺度下的测量将在非常高的质量尺度和小的混合角的组合下提供重要的输入。中子EDM对于理解T-（CP-）破坏的一般模式以及宇宙中物质和反物质的不对称性的原因也很重要。这项实验将在ORNL的散斑中子源的基本中子物理束线上进行，所采用的技术与以前测量中采用的策略有质的不同。本实验的基本技术是在温度T ~ 0.5K的超流氦-4浴中形成极化中子和氦-3原子的三组分流体。这个体积中的超冷中子将由8.9埃的中子与超流体的声子碰撞产生。中子和氦-3磁偶极子在垂直于所施加的外部磁场的平面中进动，在传统的核磁共振布置中为B 0。通过测量强电场E0存在下的中子进动频率来确定nEDM，dn。平行（反平行）于B 0的电场的应用改变了拉莫尔进动频率，nu，与dn成比例。当B 0 = 30毫高斯，E0 = 50千伏/厘米时，nu = 88赫兹，对于10^-28 e-cm的EDM，频移为4.8毫微赫兹。在操作上，中子进动频率相对于氦-3的进动频率是通过利用强自旋相关的核俘获反应和通过在液态氦-4中产生的闪烁检测反冲质子和triton来测量的。极化的氦-3原子（与中子体积相同）还包括一个共磁强计（因为氦-3原子的任何EDM都被其原子电子抑制）;它们的进动直接使用SQUIDS观察。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估而被认为值得支持。