Polarization probe for beta-decaying atoms

利用TRIUMF中性原子阱（TRINAT），我们在自旋极化37K的β衰变中寻找几个角相关的千分之一精度，以寻找标准模型中没有的新相互作用。这样的精度将与在中子β衰变中搜索的最佳计划相竞争，并在M_W/（精度）**1/2或约2 TeV设定的尺度上探索超出标准模型的物理，与LHC互补。一项准确率为2%的测试实验确定了几个有待改进的领域，其中大部分都在项目拨款范围内。许多弱衰变实验受限于对衰变物质绝对极化的了解。我们通过一种非破坏性原子技术来测量衰变37K原子的原位极化，该技术将一小部分未极化原子光电化并收集。该技术在早期发表的实验中以2%的统计精度工作，但我们已经大大提高了极化，因此可以探测的非极化原子要少得多。这笔拨款用于一种可以按需脉冲的光电离激光器，这将使我们在偏振周期的有利时间进行探测，将我们的信噪比提高两个数量级。这将使我们达到我们的设计灵敏度。否则，关于偏振的知识就会成为我们的极限系统误差。它还可以让我们在极化时直接成像原子的分布，消除另一个重要的系统误差。一个相关的要求是3个大面积微通道板，离子和电子探测器的常用备件。我们正在实现从德州农工大学的同事那里继承来的电子探测器，并使用我们现有的备件来替换那些随着时间的推移而退化的备件。大的区域将使我们能够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，一些原子电子处于更高的能量——而位置灵敏度将有助于光电子诊断的信号/噪声。这些技术将继续被我们现在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与暑期本科生使用和优化。过去，光电离部分的实验规模为本科生提供了一个很好的参与场所，因为光学只是需要耐心，而原子物理涉及扩展教科书上的量子力学。

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.