$^3$ He冷中子俘获中宇称破坏不对称性的首次精确测量
First Precision Measurement of the Parity Violating Asymmetry in Cold Neutron Capture on $^3$He
摘要：
我们报告的第一个精确测量宇称违反不对称的质子发射方向相对于中子自旋，在反应$^{3}\mathrm{He}(\mathrm{n},\mathrm{p})^{3}\mathrm{H}$，使用极化冷中子在非极化的活性$^3\rm{He}$目标的捕获。这种不对称性是核子之间的弱相互作用的结果，这仍然是电弱理论中最不了解的方面之一。该测量为现代有效场论（EFT）计算提供了重要的基准。像这样的测量对于确定强子弱相互作用的自旋-同位旋结构是必要的。我们的不对称结果是$A_{PV} = \left( 1.58 \pm 0.97 ~\mathrm{(stat)} \pm 0.24~\mathrm{(sys)}\right)\times10^{-8}$，它是迄今为止所有宇称违反不对称测量中不确定性最小的。
英文摘要：
We report the first precision measurement of the parity-violating asymmetry in the direction of proton emission with respect to the neutron spin, in the reaction $^{3}\mathrm{He}(\mathrm{n},\mathrm{p})^{3}\mathrm{H}$, using the capture of polarized cold neutrons in an unpolarized active $^3\rm{He}$ target. The asymmetry is a result of the weak interaction between nucleons, which remains one of the most poorly understood aspects of electro-weak theory. The measurement provides an important benchmark for modern effective field theory (EFT) calculations. Measurements like this are necessary to determine the spin-isospin structure of the hadronic weak interaction. Our asymmetry result is $A_{PV} = \left( 1.58 \pm 0.97 ~\mathrm{(stat)} \pm 0.24~\mathrm{(sys)}\right)\times10^{-8}$, which has the smallest uncertainty of any parity-violating asymmetry measurement so far.
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