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.

为了在我们当前的理解之外搜索新的自然定律，研究人员可以使用非常高的能量加速器，例如CERN的大型强子对撞机，或者它们可以对基本粒子特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，宇宙现在比反物质更普通的物质，但是没有已知粒子相互作用的机制可以解释宇宙在大爆炸之时从物质 - 抗逆击事件的平衡中演变而成，到现在，高度不平衡的情况。通过进行精确测量，可以在大爆炸时常见的早期颗粒和相互作用的回声，例如中子的电偶极矩等数量。中子的特征反映了中子内部正和负电荷的分离。该奖项支持设计和构建高度专业化的仪器，这些仪器是精确衡量中子的电偶极时刻所需的。除了促进亚原子物理和宇宙学方面的知识以及产生技术进步之外，该实验还将涉及博士后学者，研究生和本科生作为重要的部分，为年轻的研究人员提供了极大的机会，可以在核物理学的最前沿领域推进他们的教育和培训。预计某些技术发展是因为已经授予了与实验设备有关的几个SBIR和STTR赠款。测得的上限继续限制盛行模型的扩展。如下所示，在10^-28 E-CM的尺度上的测量将在非常高的质量尺度和小混合角的组合下提供重要的输入。中子EDM对于理解T-（CP-）违规的一般模式以及宇宙中物质和反物质不对称的原因也很重要。该实验将在ORNL的散布中子源的基本中子物理光束线上进行，它基于一种与先前测量中采用的策略在质量上不同的技术。本实验中的基本技术涉及形成偏振中子和氦3原子的三组分流体在温度t〜0.5 K处溶解在超富氦4的浴中。该体积中的超速中子将由8.9 angstrom中子与8.9 Angstrom中子产生。平面垂直于施加的外部磁场的中子和氦-3磁偶极子油在传统的核磁共振排列中B0。 NEDM DN是通过在存在强电场的情况下测量中子进动频率来确定的。电场平行（反平行）在B0上的应用会以DN的比例更改Larmor进动频率NU。在B0 = 30毫升和E0 = 50千瓦/厘米的情况下，NU = 88 Hertz，EDM为10^-28 E-CM的频移为4.8纳米赫兹。在操作上，通过利用强旋转的核捕获反应并通过液体氦4中产生的闪烁，通过利用强旋转核捕获反应并检测到后旋质捕获反应，并检测到后旋的核捕获反应并检测到后旋的核捕获反应，从而测量了中子进动频率。极化氦3原子（与中子相同的体积）也包含共磁性计（因为其原子电子抑制了氦3原子的任何EDM）；该奖项反映了NSF的法定任务，并被认为是值得通过基金会的知识分子优点和更广泛的影响审查标准来评估的。