Polarization probe for beta-decaying atoms

利用TRIUMF中性原子阱（TRINAT），我们在自旋极化37 K的β衰变中寻找几种角关联的千分之一精度，以寻找标准模型中没有的新相互作用。这样的精度将与中子β衰变中最好的计划搜索竞争，并在M_W/（精度）**1/2或约2 TeV的尺度上探索标准模型之外的物理，与LHC互补。一个2%准确率的测试实验已经确定了几个有待改进的领域，其中大部分都在项目赠款范围内。 许多弱衰变实验受到衰变物质绝对极化知识的限制。我们测量的偏振衰减的37 K原子原位的非破坏性的原子技术，光电离和收集一小部分的非偏振原子。该技术在早期发表的实验中以2%的统计精度工作，但我们已经大大改善了偏振，因此需要探测的非偏振原子要少得多。这项拨款是用于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期间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。这将使我们实现我们的设计灵敏度。否则，偏振的知识将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。 一项相关的要求是3个大面积微通道板，离子和电子探测器的共同备件。我们正在实施一个电子探测器继承了我们的得克萨斯州A&M的同事，并已使用我们现有的备件，以取代那些已恶化的时间。大面积将让我们收集所有的原子电子-在2012年12月用40毫米探测器进行的测量表明，一些原子电子的能量更高-而位置灵敏度将有助于光电子诊断的信号/噪声。 我们目前的博士将继续使用和优化这些技术。学生和合作社和暑期本科生学习多学科原子，激光和粒子探测技术。光致电离部分实验的规模在过去为本科生参与提供了一个很好的地方，因为光学只需要耐心，原子物理学涉及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.