Collaborative Research: Determination of the Neutron Lifetime Using Magnetically Trapped Neutrons

合作研究：利用磁俘获中子测定中子寿命

• 批准号: 0354264
• 负责人: John Doyle
• 金额: --
• 依托单位: Harvard University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2004
• 资助国家: 美国
• 起止时间: 2004-06-01 至 2007-11-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0354264&HistoricalAwards=false
• 关键词: Collaborative; Research; Determination; Neutron; Lifetime

The decay of the free neutron is the simplest nuclear beta decay. Theparameters that describe the decay of the free neutron, especially theneutron lifetime, provide essential inputs to all investigations thatinvolve the weak interaction. A precise value for the neutron lifetimeis required for several internal consistency tests of the StandardModel. The neutron lifetime is also an essential parameter in thetheory of Big Bang Nucleosynthesis (BBN). At present, the uncertaintyin the neutron lifetime currently provides the largest contribution tothe uncertainty in the value of the helium to hydrogen ratio predictedby BBN theory. Intercomparison between the neutron lifetime, theobserved cosmic light element abundances and the known number of lightneutrino species provides a critical consistency check for BBN theory.This experiment will measure the neutron lifetime using magneticallytrapped ultracold neutrons (UCN). A magnetic trap is ``filled'' byscattering a beam of low-energy neutrons from superfluid helium. Someneutrons lose enough energy to become trapped, with the remainderleaving the trapping region. The beam is then turned off and the rateof neutron decay, and thus their lifetime, is measured as these trappedneutrons undergo beta-decay. This technique should allow theresearchers to substantial improve the precision that the neutron betadecay lifetime is known. Using the method of magnetic trapping, itshould be possible to improve the accuracy of the neutron lifetime by afactor of between 2 and 50 using existing and next-generation neutronsources.

自由中子的衰变是最简单的核β衰变。 描述自由中子衰变的参数，特别是中子寿命，为所有涉及弱相互作用的研究提供了必要的输入。 中子寿命的精确值是标准模型的几个内部一致性测试所必需的。 中子寿命也是大爆炸核合成（BBN）理论中的一个重要参数。 目前，中子寿命的不确定性对BBN理论预测的氦氢比值的不确定性贡献最大。 中子寿命、观测到的宇宙轻元素丰度和已知的轻中微子种类数之间的相互比较为BBN理论提供了一个关键的一致性检验。 磁阱是通过从超流氦中散射出一束低能中子来“填充”的。 有些中子会失去足够的能量而被俘获，并离开俘获区。 然后关闭电子束，当这些被俘获的中子经历β衰变时，测量中子衰变的速率，从而测量它们的寿命。 这项技术将使研究人员能够大大提高中子衰变寿命的精确度。 使用磁捕获的方法，它应该是可能的，以提高精度的中子寿命的一个因素之间的2和50使用现有的和下一代的中子源。