RUI: The aCORN Experiment to Measure the Beta-Neutrino Asymmetry in Neutron Decay

艾科恩的合作意在测量中子衰变中的β-中微子不对称性，a，相对不确定度为1%。自由中子的衰变为探索弱电相互作用标准模型的极限提供了一个近乎理想的系统。目前一些标准模型的自洽测试受到a中4%的实验不确定度的限制。a的改进测量也提供了一种新的方法来测量被称为VUD的相关量，该方法不需要中子偏振测量。橡子实验依赖于将NIST冷中子束中的中子衰变分为两类：一类是贝塔和中子几乎平行发射，另一类是它们反平行发射。一组电场和磁场将粒子引导到3米长真空室两端的探测器，将a的测定简化为计算两类质子的数量。在研究潜在的系统误差来源方面付出了相当大的努力，该装置已被设计为将系统误差降低到0.5%以下。该仪器目前正在印第安纳大学组装，为转移到NIST做准备。系统误差的一个主要来源是磁场和确定实验轴的准直器之间的不对准。我们已经设计了一种测绘和对准程序，将在印第安纳州进行测试，现在我们建议在NIST构成的更困难的磁环境中重复该程序。此外，我们将通过测量质子探测器位置的热灯丝中的电子分布来直接测量系统的对准程度。在汉密尔顿进行样机测试后，我们将在NIST的橡子设备中进行最终的对准检查。这项工作将继续涉及大量的本科生，无论是在汉密尔顿还是在NIST。这将允许来自一所小型学院的本科生拥有汉密尔顿实验的一部分，然后在国家实验室的新环境中看到他们的部分集成到最终系统中。

The aCORN collaboration intends to measure the beta-neutrino asymmetry, a, in neutron decay with a relative uncertainty of 1%. The decay of the free neutron provides a nearly ideal system in which to probe the limits of the Standard Model of the electroweak interaction. Some current tests of the self-consistency of the Standard Model are limited by the 4% experimental uncertainty in a. An improved measurement of a also provides a new method to measure a related quantity known as Vud that does not require neutron polarimetry. The aCORN experiment relies on separating neutron decays from a cold neutron beam at NIST into two classes; one in which the beta and neutron are emitted nearly parallel, and one in which they are anti-parallel. A set of electric and magnetic fields guide the particles to detectors at opposite ends of a 3m long vacuum vessel reducing the determination of a to counting the numbers of protons in the two classes. Considerable effort has gone into studying potential sources of systematic error, and the apparatus has been designed to reduce systematic errors below 0.5%. The apparatus is currently being assembled at Indiana University in preparation for a move to NIST. A principle source of systematic error is mis-alignment between the magnetic field and the collimators that define the experimental axis. We have devised a mapping and alignment procedure that will be tested at Indiana, and we now propose to repeat the procedure in the more difficult magnetic environment posed by NIST. In addition we will directly measure the alignment of the system by measuring the distribution of electrons from a hot filament at the proton detector position. After prototype testing at Hamilton, we will implement the final alignment check in the aCORN apparatus at NIST. The work will continue to involve significant numbers of undergraduates, both at Hamilton and at NIST. This will allow undergraduates from a small college to take ownership of a portion of the experiment Hamilton, and then to see their piece integrated into the final system in the new environment of a national laboratory.