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衰变表明，自然确实违反了被认为是非常基本的对称性的东西：平等（通过镜子看世界）。 通过测量偏振中子和电子衰减成质子时发出的电子之间的方向相关性，该测量的精确度得到了极大的提高，使我们能够再次探测超出“标准模型”的探测。加上中子和穆恩寿命 - 我们可以测试我们对Quark'混合'的理解是否完成。 （中子有两个“下降”和一个“向上”夸克，而质子的质子有两个“向上”，一个“向上”夸克 - 在中子betadecay中，一个'down'quark变成了“上”夸克。）如果当前的图片正确，则夸克混合矩阵应该统一（很像矢量的长度在您旋转其旋转系统时不会变化）。 单位性的任何偏差都会显示出工作中的新物理学，并且至关重要。为了衡量这种相关性，我们在洛斯阿拉莫斯国家实验室（Los Alamos National Laboratory）创建“超冷的中子”（UCN）（UCN），该实验室完全反思 - 就像光纤中的光一样 - 非常像光学的光 - 意味着这些中子可以在特殊的引导和易于极化的偏移中运输。这大大减少了由于横梁引起的背景和不完全极化而导致的系统错误。我们表明，最好的指南是钻石涂层，我们在弗吉尼亚理工大学（带有此拨款）使用“脉冲激光沉积”的“钻石样碳”。 中子在两极分化的位置的上游我们也可以使用镍58涂层，我们也可以使用。在其最终调试阶段进行了实验，并且已经进行了几次测试。 我们预计，今年对中子的beta不对称性进行了第一％的测量，并带来UCN实验的所有优势，以达到我们完成之前的目标，达到了0.2％的目标。这笔拨款还支持我们为数据采用系统努力运行实验。