Polarized Ultra-Cold Neutron Transport for Neutron Beta Decay Asymmetry Measurements

原子核的β衰变在标准模型的形成过程中起着重要的作用，而且它在研究标准模型之外的物理学过程中也一直起着重要的作用。研究β衰变的最简单的系统是中子。 通过测量中子的寿命（从Ft值）和中子的β不对称性A，人们有足够的信息来独立地确定弱矢量和轴向矢量耦合，GV和GA。 一个批准的实验（位于洛斯阿拉莫斯）将再次测量A系数，利用超冷中子（UCN），大大减少系统误差，否则由于光束诱导的背景和不完全极化。 其主要特点是：1）能够将中子输送到离其产生地点相当远的地方; 2）当束脉冲到达目标时，可以否决事件; 3）使用轴向磁场获得100%的极化。这项建议包括努力开发一种用于传输极化中子的最佳涂层，并为实验实现一个合适的DAQ系统。看来脉冲激光沉积（PLD）金刚石薄膜可能是合适的。一个成功的活动，使适当的涂层导向器将产生重大影响，不仅对这个实验，而且对计划中的未来实验也是如此。

Nuclear beta decay was important in motivating the Standard Model, andit continues to be of importance in searches for physics beyond the Standard Model.The simplest system for studying beta decay is the neutron. By measuring theneutron's lifetime (from the Ft value) and the neutron's beta asymmetry A, onehas enough information to independently determine the weak vector and axial-vectorcouplings, GV and GA. An approved experiment (located at Los Alamos) will again measure the A coefficient,utilizing Ultra-Cold Neutrons (UCN), dramatically reducing systematic errors otherwisepresent due to beam-induced backgrounds and incomplete polarization. The keyfeatures are 1) the ability to port the neutrons to a significant distance awayfrom their production site, 2) vetoing events when the beam pulse is on target,and 3) obtain 100% polarization using an axial magnetic field. This proposal covers efforts to develop an optimum coating fortransporting polarized neutrons, and implementing a suitable DAQ system for the experiment.It appears pulsed-laser-deposition (PLD) diamond films may be suitable.A successful campaign to make suitably coated guides would havean significant impact, not just for this experiment, but planned futureexperiments as well.5