Search for explanation of the neutron lifetime anomaly
Search for explanation of the neutron lifetime anomaly
复制标题
寻找中子寿命异常的解释
DOI：
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发表时间：
2020
期刊：
影响因子：
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通讯作者：
A. Chechkin
中科院分区：
文献类型：
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作者：
A. Serebrov;M. Chaikovskii;G. Klyushnikov;O. Zherebtsov;A. Chechkin
近20年来用UCN储存方法进行的所有中子寿命测量结果都很吻合。这些结果也与标准模型中最新最精确的中子衰变不对称性测量结果一致。然而，在$3.6sigma$（衰减概率的1%）水平上，存储方法实验的平均结果与束法获得的最精确值之间存在显著差异。本文讨论了造成这种差异的可能原因。我们的重点是在光束实验中寻找可能的系统修正谱。审议了以前没有适当处理的系统误差的四个不同来源。其中两个源与质子在电磁场中的运动和残余气体的弹性散射有关。这些问题与装置的几何结构和质子探测器的尺寸有关。蒙特卡罗仿真表明，这些影响可以忽略不计，不影响测量结果。第三个误差与探测器死层中的质子损失有关。结果表明，这种修正需要比描述光束测量方法的论文更详细的分析。系统误差的第四个来源是残余气体上的电荷交换过程。在束流法实验中忽略了残余气体的影响。我们提出的论点是，仔细分析这个问题是必要的，因为提出的质子损失修正减少了测量寿命，使其更接近存储方法的结果。研究了有关这一问题的可能修正谱，并表明为了得到精确的结果，有必要直接测量质子阱内残余气体的浓度和组成。
All results of the neutron lifetime measurements performed in the last 20 years with the UCN storage method are in a good agreement. These results are also consistent with the latest most accurate measurements of the neutron decay asymmetry within the Standard Model. However, there is a significant discrepancy at $3.6sigma$ (1% of the decay probability) level between the averaged result of the storage method experiments and the most precise value obtained with the beam method. This article addresses the possible causes of that discrepancy. We focused on finding the spectrum of possible systematic corrections in the beam experiment. Four separate sources of the systematic errors which had not been properly addressed previously were considered. Two of those sources are related with the motion of protons in an electromagnetic field and the elastic scattering by the residual gas. These problems are associated with the geometrical configuration of the setup and the proton detector size. The Monte-Carlo simulation shows that these effects are negligible and do not affect measurement results. The third error concerns proton loss in the dead layer of the detector. It is shown that this correction requires a more detailed analysis than that given in the papers describing the beam measurement method. The fourth source of the systematic error is the charge exchange process on the residual gas. The influence of the residual gas was neglected in the beam method experiment. We present arguments that careful analysis of this issue is necessary since the proposed proton losses correction decreases the measured lifetime bringing it closer to the storage method results. Spectrum of possible corrections concerning this issue is investigated and it is shown that for the precise result, it is necessary to directly measure the concentration and composition of the residual gas inside the proton trap.