4 He中宇称破坏中子自旋转动的实验上限和理论期望
Experimental Upper Bound and Theoretical Expectations for Parity-Violating Neutron Spin Rotation in 4He
摘要：
在标准模型中，夸克-夸克弱相互作用会导致中子自旋旋转，从而在核子之间产生违反宇称的弱相互作用。本文给出了在液态$^{4}$ He介质中极化中子自旋旋转引起宇称破缺效应的实验结果。$^{4}$ He中每单位长度的中子自旋旋转角值$dϕ/dz =(+2.1 \pm 8.3 (stat.) \pm 2.9 (sys.))\times10^{-7}$ rad/m与零一致。这一结果与其它实验对核子-核子弱振幅大小的最佳理论估计以及最近对核子-核子弱相互作用理论方法的预期一致。本文回顾了$\vec{n}+^{4}$ He系统宇称破缺的理论状况，并讨论了导致上述结果的数据分析的细节。分析工具，量化系统的不确定性，在这种测量，预计将是必不可少的未来的测量。
英文摘要：
Neutron spin rotation is expected from quark-quark weak interactions in the Standard Model, which induce weak interactions among nucleons that violate parity. We present the results from an experiment searching for the effect of parity violation via the spin rotation of polarized neutrons in a liquid $^{4}$He medium. The value for the neutron spin rotation angle per unit length in $^{4}$He, $dϕ/dz =(+2.1 \pm 8.3 (stat.) \pm 2.9 (sys.))\times10^{-7}$ rad/m, is consistent with zero. The result agrees with the best current theoretical estimates of the size of nucleon-nucleon weak amplitudes from other experiments and with the expectations from recent theoretical approaches to weak nucleon-nucleon interactions. In this paper we review the theoretical status of parity violation in the $\vec{n}+^{4}$He system and discuss details of the data analysis leading to the quoted result. Analysis tools are presented that quantify systematic uncertainties in this measurement and that are expected to be essential for future measurements.
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