Transport of Polarized Ultra Cold Neutrons for UCN-A Fundamental Symmetry Study

用于 UCN-A 基本对称性研究的极化超冷中子输运

• 批准号: 0700491
• 负责人: ROBERT VOGELAAR
• 金额: $ 35.48万
• 依托单位: Virginia Polytechnic Institute and State University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2007
• 资助国家: 美国
• 起止时间: 2007-06-01 至 2011-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0700491&HistoricalAwards=false
• 关键词: Transport; Polarized; Ultra; Cold; Neutrons

Nuclear beta decay revealed that Nature indeed violates what had been thought to be a very fundamental symmetry: parity (looking at the world through a mirror). Greatly improved precision of this measurement lets us again probe beyond the 'Standard Model'.By measuring the directional correlation between a polarized neutron and the electron emitted when it decays into a proton - coupled with the neutron and muon lifetimes - we can test whether our understanding of quark 'mixing' is complete. (A neutron has two 'down' and one 'up' quarks, while the proton has two 'up' and one 'down' quarks - in neutron betadecay a 'down' quark becomes an 'up' quark.)If the current picture is correct, the quark mixing matrix should be unitary (much like the length of a vector doesn't change when you rotate its coordinate system). Any deviationfrom unitarity would show new physics at work and be of fundamental importance.To measure this correlation, we create 'Ultra-Cold Neutrons' (UCN) at the Los Alamos National Laboratory which undergo total reflection - much like light in fiber optics - meaning these neutrons can be transported long distances in special guides and are also easily polarized. This dramatically reduces systematic errors otherwise present due to beam-induced backgrounds and incomplete polarization.We have shown that the best guides are diamond coated, which we fabricate at Virginia Tech (with this grant) using 'pulsed laser deposition' of 'diamond-like carbon'. Upstream of where the neutrons get polarized we can also use Nickel-58 coatings, which we are also able to to.The experiment in in its final commissioning stages, and several test runs have already been made. We anticipate getting our first one percent measurement of the neutron's beta asymmetry this year, and bringing to bear all the advantages of a UCN experiment to reachthe goal of 0.2% before we are finished.This grant also supports our efforts for the data acquisition system to run the experiment.

核β衰变揭示了大自然确实违反了人们认为非常基本的对称性：宇称（通过镜子看世界）。 这种测量精度的大幅提高让我们再次超越了“标准模型”。通过测量极化中子和衰变成质子时发射的电子之间的方向相关性--再加上中子和μ子的寿命--我们可以测试我们对夸克“混合”的理解是否完整。 （一个中子有两个“下”夸克和一个“上”夸克，而质子有两个“上”夸克和一个“下”夸克--在中子10代中，一个“下”夸克变成了一个“上”夸克。如果当前的图像是正确的，夸克混合矩阵应该是幺正的（就像当你旋转一个矢量的坐标系时，它的长度不会改变）。 任何对幺正性的偏离都将表明新的物理学在起作用，并具有根本的重要性。为了测量这种相关性，我们在洛斯阿拉莫斯国家实验室创造了“超冷中子”（UCN），它会经历全反射--就像光纤中的光一样--这意味着这些中子可以在特殊的波导中长距离传输，也很容易极化。这大大减少了系统误差，否则由于光束诱导的背景和不完全极化。我们已经表明，最好的指南是金刚石涂层，我们在弗吉尼亚理工大学制造（与此授权）使用“脉冲激光沉积”的“类金刚石碳”。 在中子极化的上游，我们也可以使用镍-58涂层，我们也可以这样做。实验处于最后的调试阶段，已经进行了几次试运行。 我们预计今年将获得中子β不对称性的第一个1%的测量结果，并在完成之前利用UCN实验的所有优势达到0.2%的目标。这笔赠款还支持我们为数据采集系统运行实验所做的努力。