Time Reversal, Neutron Structure, and Neutron Beta Decay

核和中子极化的工具允许研究时间反转和宇称的对称性，这些对称性可以用于研究存在更强相互作用的弱相互作用。时间反转对称性及其违反是理解基本粒子水平物理和解决问题的关键：物质对反物质的优势是如何产生的。极化中子衰变中的时间反转或粒子运动和自旋提供了对宇称偶时反转奇物理的探索，以及对某些尚未观察到的相互作用的独特看法。在盖瑟斯堡地址的NIST用冷中子束设计了一个实验来测量电子和质子动量与衰变中子自旋的三矢量相关。中子的电荷分布最好用电子或3He电子对极化中子的散射来研究。虽然中性，但中子电荷半径和电形状因子所表征的电荷的细微分布在强相互作用中有着根本的根源。在洛斯阿拉莫斯进行的冷极化中子束实验和在麻省理工学院/贝茨进行的极化电子散射实验旨在解决这些问题。中子和质子之间的弱相互作用从未被直接观察到，尽管重核的电流分布特征以及核态的宇称混合已经被观察到。在洛斯阿拉莫斯，一项实验正在进行中，该实验首次使用在液态对氢上捕获的极化冷中子束来测量这种耦合。包括弱相互作用修正在内的核子-核子力模型预测了一系列数值。测量到10%应该会限制这个范围，并证实其他观察结果，包括原子宇称破坏中测量的113CS的准极点矩。

The tools of nuclear and neutron polarization allow investigation of the symmetries of time reversal and parity that can be used to study weak interactions in the presence of much stronger interactions. Time reversal symmetry and its violation are key to understanding physics at the elementary particle level and to address the question: how has the predominance of matter over anti matter been generated. The reversal of time or motion of particles and spins in the decay of polarized neutrons provides a probe of parity even - time reversal odd physics and a unique view of certain kinds of interactions not yet observed. An experiment with the cold neutron beam at NIST, Gaithersburg addresses is designed to measure the triple vector correlation of electron and proton momenta with decaying neutron spin. The charge distribution of the neutron can best be studied by scattering of polarized neutrons by electrons or of electrons from 3He. Though neutral, the subtle distribution of charge characterized by the neutron charge radius and electric form factor has a fundamental origin in the strong interaction. Experiments with a cold polarized neutron beam at Los Alamos and with polarized electrons scattering at MIT/Bates are designed to address these questions. The weak interaction between neutrons and protons has never been directly observed, though features of the current distribution of the heavy nuclei as well as parity mixing of nuclear states has been observed. At Los Alamos, an experiment is under development to use a polarized cold neutron beam captured on liquid parahydrogen to measure this coupling for the first time. Models of the nucleon-nucleon force including the weak interaction corrections predict a range of values. Measurement to 10% should restrict this range and corroborate other observations including the anapole moment of 113CS measured in atomic parity violation.