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.

这个奖项将支持PI和本科生与他一起工作，以了解中子衰变的方式以及自由中子在衰变前存在多久。 不被束缚在原子核中的中子将在大约880秒内衰变为质子、电子和反中微子。 研究中子的这种性质的特征，随着精度的提高，可以更深入地了解宇宙赖以建立的框架。一个名为aCORN的实验在美国国家标准与技术研究所中子研究中心收集数据，以比以往任何时候都更精确地测量电子和反中微子发射方向之间的相关性。 另一个实验，UCNTau，是使用磁铁和重力来捕获非常低能量的中子，以测量中子的寿命不到一秒。实验捕获非常低的能量中子，并随后在一段时间后计数未衰变的幸存者，往往会给出与涉及更高能量的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是非常有趣的，因为它有可能揭示中子衰变的新特征。该奖项将允许主要研究者（PI）和DePauw大学本科研究人员为这两个实验做出重要贡献。 aCORN实验一直是PI研究计划的旗舰项目，在许多方面都是他的学生为研究和教学做准备的训练场。 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领域的职业生涯做好准备，或者在STEM领域攻读研究生学位。反中微子关联包括电弱标准模型的改进的模型无关检验和不依赖于弱轴向矢量与矢量耦合常数之比的测量。中子偏振测量法此外，这种测量，沿着更精确的中子寿命，将允许仅从自由中子衰变确定Vud -Cabbibo-Kobayashi-Maskawa（CKM）矩阵的元素，因此不受核结构相关校正的影响。由于CKM矩阵必须是一元矩阵，这将提供对标准模型的测试。 更好地了解中子寿命也允许对大爆炸核合成进行严格的测试。 aCORN实验依赖于同时检测电子和质子来推断反中微子的相对发射方向。PI开发了一个质子跟踪模拟，用于确定aCORN质子聚焦系统对第一个数据集的效率，这对于确定不完美质子探测导致的系统误差的大小至关重要。PI将对第二个数据集应用该分析，并全面分析NG-C数据。在aCORN质子模拟中使用的技术将被用来设计UCNTau实验中的质子探测器系统，以允许通过观察更接近中子束寿命实验实际测量的质子来确定中子寿命。这种测量可能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.