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: 0354263
• 负责人: Paul Huffman
• 金额: --
• 依托单位: North Carolina State 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 2009-11-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0354263&HistoricalAwards=false
• 关键词: Collaborative; Research; Determination; Neutron; Lifetime

The decay of the free neutron is the simplest nuclear beta decay. The parameters that describe the decay of the free neutron, especially the neutron lifetime, provide essential inputs to all investigations that involve the weak interaction. A precise value for the neutron lifetime is required for several internal consistency tests of the Standard Model. The neutron lifetime is also an essential parameter in the theory of Big Bang Nucleosynthesis (BBN). At present, the uncertainty in the neutron lifetime currently provides the largest contribution to the uncertainty in the value of the helium to hydrogen ratio predicted by BBN theory. Intercomparison between the neutron lifetime, the observed cosmic light element abundances and the known number of light neutrino species provides a critical consistency check for BBN theory.This experiment will measure the neutron lifetime using magnetically trapped ultracold neutrons (UCN). A magnetic trap is "filled" by scattering a beam of low-energy neutrons from superfluid helium. Some neutrons lose enough energy to become trapped, with the remainder leaving the trapping region. The beam is then turned off and the rate of neutron decay, and thus their lifetime, is measured as these trapped neutrons undergo beta-decay. This technique should allow the researchers to substantial improve the precision that the neutron beta decay lifetime is known. Using the method of magnetic trapping, it should be possible to improve the accuracy of the neutron lifetime by a factor of between 2 and 50 using existing and next-generation neutron sources.

自由中子的衰变是最简单的核β衰变。 描述自由中子的衰减的参数，尤其是中子寿命，为所有涉及弱相互作用的研究提供了必不可少的输入。 标准模型的几个内部一致性测试需要中子寿命的精确值。 中子寿命也是大爆炸核合成理论（BBN）的重要参数。目前，中子寿命的不确定性目前为BBN理论预测的氦气与氢比的价值的不确定性提供了最大的贡献。 中子寿命，观察到的宇宙光元素丰度和已知的光中微子物种之间的比较，为BBN理论提供了关键的一致性检查。该实验将使用磁性捕获的超级枚中子（UCN）测量中子寿命。 通过从超流体氦气中散射一束低能中子的光束，“填充”磁陷阱。 一些中子会失去足够的能量被困，其余的离开陷阱区域。 然后关闭梁，中子衰减的速率，因此将其寿命测量为这些被困的中子经历β-末期。 该技术应使研究人员可以大大提高中子β衰变寿命的精度。 使用磁陷阱的方法，应该使用现有和下一代中子源将中子寿命的准确性提高2至50倍。