Penttila S I, Bowman J D
Los Alamos National Laboratory Los Alamos, NM 87545.
J Res Natl Inst Stand Technol. 2005 Jun 1;110(3):309-13. doi: 10.6028/jres.110.045. Print 2005 May-Jun.
The abBA collaboration is developing a new type of field-expansion spectrometer for a measurement of the three correlation coefficients a, A, and B and the shape parameter b. The measurement of A and B requires precision neutron polarimetry. We will polarize a pulsed cold neutron beam from the SNS using a (3)He neutron spin filter. The well-known polarizing cross section for n-(3)He has a 1/v dependence, where v is the neutron velocity, which is used to determine the absolute beam polarization through a time-of-flight (TOF) measurement. We show that by measuring the TOF dependence of A and B, the coefficients and the neutron polarization can be determined with a small loss of the statistical precision and with negligible systematic error. We conclude that it is possible to determine the neutron polarization averaged over a long run in the neutron beta decay experiment with a statistical error less than 10(-4). We discuss various sources of systematic uncertainty in the measurement of A and B and conclude that the fractional systematic errors are less than 2 × 10(-4).
abBA合作团队正在开发一种新型的场扩展光谱仪，用于测量三个相关系数a、A和B以及形状参数b。测量A和B需要精确的中子极化测量。我们将使用一个³He中子自旋滤波器对来自SNS的脉冲冷中子束进行极化。众所周知，n-³He的极化截面与1/v相关，其中v是中子速度，通过飞行时间（TOF）测量来确定绝对束极化。我们表明，通过测量A和B对TOF的依赖性，可以在统计精度损失较小且系统误差可忽略不计的情况下确定系数和中子极化。我们得出结论，在中子β衰变实验中，有可能以小于10⁻⁴的统计误差确定长期平均的中子极化。我们讨论了测量A和B时各种系统不确定性的来源，并得出分数系统误差小于2×10⁻⁴的结论。
