RUI: Precision Measurements of Free Neutron Decay Observables

RUI：自由中子衰变可观测量的精确测量

• 批准号: 1714461
• 负责人: Alexander Komives
• 金额: $ 9万
• 依托单位: DePauw University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2017
• 资助国家: 美国
• 起止时间: 2017-08-15 至 2022-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1714461&HistoricalAwards=false
• 关键词: RUI; Precision; Measurements; Free; Neutron

This award will support the PI and undergraduate students working with him to understand the ways in which neutrons decay and how long a free neutron will exist before decaying. Neutrons which are not bound in an atomic nucleus will decay in about 880 seconds into a proton, electron and an antineutrino. Studying characteristics of this property of neutrons with increasing precision allows a deeper knowledge about the framework upon which the cosmos was built. One experiment, named aCORN, has collected data at the National Institute of Standards and Technology Center for Neutron Research to measure the correlation between the emission directions of the electron and antineutrino more precisely than ever before. Another experiment, UCNtau, is using magnets and gravity to trap very low energy neutrons to measure the neutron's lifetime to less than a second. Experiments trapping very low energy neutrons and subsequently counting the undecayed survivors after a period of time are tending to give results significantly different than experiments which involve a higher energy beam of neutrons and the detection of protons produced in the decay. Finding the cause of this discrepancy is of great interest as it has the potential of uncovering a new feature of neutron decay. This award will allow the Principle Investigator (PI) and DePauw University Undergraduate Researchers to make important contributions to these two experiments. The aCORN experiment has been the flagship project of the PI's research program, which in many ways has acted as a training ground for his students to prepare them for research and teaching. The students who participate in this research gain a broad range of hardware and software skills that prepare them for careers in STEM fields or to pursue graduate degrees also in STEM areas.The motivations for a more precise measurement of the electron-antineutrino correlation include an improved model independent test of the Electroweak Standard Model and a measurement of the ratio of weak axial vector to vector coupling constants that does not depend on neutron polarimetry. In addition, this measurement, along with a more precise neutron lifetime, would allow a determination of Vud - an element of the Cabbibo-Kobayashi-Maskawa (CKM) matrix - solely from free neutron decay and thus not complicated by nuclear structure dependent corrections. As the CKM matrix is required to be unitary, this would provide a test of the Standard Model. Knowing the neutron lifetime better also allows for a stringent test of Big Bang Nucleosynthesis. The aCORN experiment depends on the simultaneous detection of electrons and protons to infer the relative emission direction of the antineutrino. The PI has developed a proton tracking simulation that determines the efficiency of the aCORN proton focusing system for the first data set which is important in establishing the size of the systematic error that would result from imperfect proton detection. The PI will apply this analysis to the second data set and fully analyze the NG-C data. The techniques used in the aCORN proton simulation will be employed to design a proton detector system in the UCNtau experiment to allow determination of the neutron lifetime by observation of the protons which is closer to what the neutron beam lifetime experiments actually measure. Such a measurement could be instrumental in understanding the discrepancy between these experiments.

该奖项将支持 PI 和与他一起工作的本科生了解中子衰变的方式以及自由中子在衰变之前会存在多长时间。 未束缚在原子核中的中子将在大约 880 秒内衰变成质子、电子和反中微子。 通过越来越精确地研究中子的这种特性，可以更深入地了解宇宙的构建框架。一项名为 aCORN 的实验在国家标准研究院中子研究中心收集了数据，以比以往更精确地测量电子和反中微子发射方向之间的相关性。 另一项实验 UCNtau 正在利用磁铁和重力来捕获能量非常低的中子，以测量中子的寿命，使其小于一秒。捕获能量非常低的中子并随后在一段时间后计算未衰变幸存者的实验往往会得出与涉及较高能量中子束和检测衰变中产生的质子的实验明显不同的结果。找到这种差异的原因非常有意义，因为它有可能揭示中子衰变的新特征。该奖项将使首席研究员（PI）和迪堡大学本科研究人员能够为这两项实验做出重要贡献。 aCORN 实验一直是 PI 研究计划的旗舰项目，该项目在很多方面都充当了他的学生的训练场，为他们的研究和教学做好准备。 参与这项研究的学生获得了广泛的硬件和软件技能，为他们在 STEM 领域的职业生涯或在 STEM 领域攻读研究生学位做好了准备。更精确地测量电子-反中微子相关性的动机包括改进电弱标准模型的模型独立测试以及不依赖于中子极化测量的弱轴向矢量与矢量耦合常数之比的测量。此外，这种测量以及更精确的中子寿命将允许仅通过自由中子衰变来确定 Vud（Cabbibo-Kobayashi-Maskawa (CKM) 矩阵的元素），因此不会因核结构相关校正而变得复杂。由于 CKM 矩阵要求是酉的，因此这将提供标准模型的测试。 更好地了解中子寿命还可以对大爆炸核合成进行严格的测试。 aCORN实验依靠电子和质子的同时检测来推断反中微子的相对发射方向。 PI 开发了一种质子跟踪模拟，可确定 aCORN 质子聚焦系统对第一个数据集的效率，这对于确定因不完美的质子检测而导致的系统误差的大小非常重要。 PI 将此分析应用于第二个数据集并全面分析 NG-C 数据。 aCORN 质子模拟中使用的技术将用于设计 UCNtau 实验中的质子探测器系统，以便通过观察质子来确定中子寿命，这更接近中子束寿命实验实际测量的结果。这样的测量有助于理解这些实验之间的差异。

项目成果

Improved Neutron Lifetime Measurement with UCNτ

• DOI: 10.1103/physrevlett.127.162501
• 发表时间: 2021-10-13
• 期刊: PHYSICAL REVIEW LETTERS
• 影响因子: 8.6
• 作者: Gonzalez, F. M.;Fries, E. M.;Young, A. R.
• 通讯作者: Young, A. R.

Measurement of the neutron lifetime using a magneto-gravitational trap and in situ detection

• DOI: 10.1126/science.aan8895
• 发表时间: 2017-07
• 期刊: Science
• 影响因子: 56.9
• 作者: R. Pattie;N. Callahan;C. Cude-Woods;E. Adamek;L. Broussard;S. Clayton;S. Currie;E. Dees;X. Ding;E. M. Engel;D. Fellers;W. Fox;P. Geltenbort;K. Hickerson;M. Hoffbauer;A. Holley;A. Komives;C-Y. Liu;S. W. T. MacDonald;M. Makela;C. Morris;J. Ortiz;J. Ramsey;D. Salvat;A. Saunders;S. Seestrom;E. Sharapov;S. Sjue;Z. Tang;J. Vanderwerp;B. Vogelaar;P. Walstrom;Z. Wang;W. Wei;H. Weaver;J. Wexler;T. Womack;A. R. Young;B. Zeck

Neutron polarimetry using a polarized 3He cell for the aCORN experiment

使用极化 3He 电池进行 aCORN 实验的中子旋光测定

• DOI: 10.1016/j.nima.2020.164862
• 发表时间: 2021
• 期刊: Detectors and Associated Equipment
• 作者: Schafer, B.C.;Byron, W.A.;Chen, W.C.;Collett, B.;Dewey, M.S.;Gentile, T.R.;Hassan, Md.T.;Jones, G.L.;Komives, A.;Wietfeldt, F.E.
• 通讯作者: Wietfeldt, F.E.

Measurement of the neutron decay electron-antineutrino angular correlation by the aCORN experiment

通过aCORN实验测量中子衰变电子-反中微子角相关性

• DOI: 10.1103/physrevc.103.045502
• 发表时间: 2021
• 期刊: Physical Review C
• 影响因子: 3.1
• 作者: Hassan, M. T.;Byron, W. A.;Darius, G.;DeAngelis, C.;Wietfeldt, F. E.;Collett, B.;Jones, G. L.;Komives, A.;Noid, G.;Stephenson, E. J.
• 通讯作者: Stephenson, E. J.