Polarization probe for beta-decaying atoms

利用TRIUMF中性原子陷阱(TRINAT)，我们寻求自旋极化37Kβ衰变中几个角关联的千分之一精度，以寻找不在标准模型中的新的相互作用。这样的精度将与中子β衰变中最好的计划搜索相竞争，并在M_W/(精度)**1/2或约2TeV设置的尺度上探索超出标准模型的物理，以补充大型强子对撞机。一项精度为2%的测试实验确定了几个需要改进的领域，其中大部分都在项目拨款范围内。许多微弱的衰变实验都受到衰变物种绝对极化知识的限制。我们用一种非破坏性原子技术原位测量衰变的37K原子的极化，这种技术光致电离并收集了一小部分未极化的原子。这项技术在早期发表的实验中以2%的统计精度工作，但我们已经极大地改善了极化，因此需要探测的未极化原子要少得多。这笔赠款是为了一种可以按需脉冲的光电离激光器，这将使我们能够在偏振周期的有利时间进行探测，将我们的信号/噪声提高约两个数量级。这将让我们实现我们的设计敏感性。否则，对极化的了解将成为我们有限的系统误差。它还可以让我们直接描绘极化时原子的分布，消除另一个重要的系统误差。一个相关的请求是3个大面积微通道板，离子和电子探测器的通用备件。我们正在实施德克萨斯A&M同事继承的电子探测器，并使用我们现有的备件来取代那些随着时间推移而变质的探测器。这个大面积的区域将让我们收集所有的原子电子--2012年12月用40毫米探测器进行的测量表明，其中一些处于更高的能量--而位置灵敏度将有助于光电子诊断的信号/噪声。这些技术将继续由我们目前的博士生以及学习多学科原子、激光和粒子探测技术的合作和暑期本科生使用和优化。过去，光电离实验的规模为本科生的参与提供了一个很好的场所，因为光学只需要耐心，原子物理涉及到扩展教科书量子力学。

Using the TRIUMF Neutral Atom Trap (TRINAT), we seek part per thousand accuracy of several angular correlations in the beta decay of spin-polarized 37K, to search for new interactions not in the standard model. Such accuracy would be competitive with the best planned searched in neutron beta decay, and explore physics beyond the Standard Model at scales set by M_W/(accuracy)**1/2 or about 2 TeV, complementary to the LHC. A test experiment at 2% accuracy has identified several areas to be improved, most covered under the project grant. Many weak decay experiments are limited by the knowledge of the absolute polarization of the decaying species. We measure the polarization of the decaying 37K atoms in situ by a non-destructive atomic technique that photoionizes and collects a small fraction of the unpolarized atoms. The technique worked in the earlier published experiment at 2% statistical accuracy, but we have improved the polarization greatly, so there are many fewer unpolarized atoms to probe. This grant is for a photoionization laser that can be pulsed on demand, which will let us probe at advantageous times during the polarization cycle, improving our signal/noise about two orders of magnitude. This will let us achieve our design sensitivity. Otherwise the knowledge of the polarization would become our limiting systematic error. It will also let us directly image the distribution of atoms while polarized, eliminating another important systematic error. A related request is for 3 large-area microchannel plates, common spares for the ion and electron detectors. We are implementing an electron detector inherited by our Texas A&M colleagues, and have used our existing spares to replace those that had deteriorated with time. The large area will let us collect all the atomic electrons-- measurements with a 40 mm detector in December 2012 suggest some are at higher energy-- while the position sensitivity will help signal/noise on the photoelectron diagnostic. The techniques will continue to be used and optimized by our present Ph.D. student and by co-op and summer undergrads learning multidisciplinary atomic, laser, and particle detection techniques. The scale of the photoionization parts of the experiment have provided a good place for undergrad participation in the past, since the optics simply requires patience, and the atomic physics involves extending textbook quantum mechanics.