Polarized Ultra-Cold Neutron Transport for UCN-A Experiment

核衰变在推动标准模型方面是很重要的，并且在探索标准模型之外的物理方面仍然很重要。研究β衰变最简单的系统是中子，对表征衰变的参数进行越来越精确的测量已经有很长的历史了。通过测量中子的寿命（从Ft值）和中子的β不对称A，人们有足够的信息来独立确定弱矢量和轴矢量耦合，GV和GA。尽管最近对中子寿命的精确测量彼此之间很好地一致，但对中子的β不对称性a的测量却不能说同样的话。自1985年以来，对a进行了四次精确测量（统计和系统的不确定度各约为1%）。不幸的是，这四次测量之间的一致性很差。经过批准的洛斯阿拉莫斯实验将再次测量A系数，这次使用超冷中子，极大地减少了由于光束诱导背景和不完全极化而出现的系统误差。关键特点是1)能够将中子转移到远离其产生地点的相当远的距离（使用全外部反射），2)当束脉冲到达目标时（利用脉冲产生方法），以及3)使用轴向磁场获得100%极化（错误自旋的中子没有足够的动能克服mu）。B可能)。我们在弗吉尼亚理工大学的小组负责UCN传输los Alamos实验，快速DAQ和实验协调。该系统的关键组成部分是用于传输极化中子的涂层。我们已经证明了脉冲激光沉积金刚石薄膜是合适的。在VirginiaTech，现有的准分子激光器已经重新投入使用，以生产合适的薄膜。研制了一种分光计导管和中心衰减管的涂膜系统。为偏光ucn制作合适涂层导板的成功活动不仅对这个实验有影响，而且对计划中的未来实验也有影响。

Nuclear beta decay was important in motivating the Standard Model, andit continues to be of importance in searches for physics beyond theStandard Model. The simplest system for studying beta decay is theneutron, where there is a long history of increasingly accuratemeasurements of the parameters that characterize the decay. Bymeasuring the neutron's lifetime (from the Ft value) and the neutron'sbeta asymmetry A, one has enough information to independently determinethe weak vector and axial-vector couplings, GV and GA. Although recentaccurate measurements of the neutron lifetime are in good agreementwith each other, the same cannot be said for measurements of theneutron's beta asymmetry A. Since 1985, there have been four accurate(combined statistical and systematic uncertainty of about 1% each)measurements of A. Unfortunately, the agreement between these four Ameasurements is poor.An approved Los Alamos experiment will again measure the A coefficient,this time utilizing Ultra-Cold Neutrons, dramatically reducingsystematic errors otherwise present due to beam-induced backgrounds andincomplete polarization. The key features are 1) the ability to portthe neutrons to a significant distance away from their production site(using total external reflection), 2) vetoing events when the beampulse is on target (capitalizing on the pulsed production method), and3) obtain 100% polarization using an axial magnetic field (whereneutrons of the wrong spin do not have enough kinetic energy toovercome the mu.B potential).Our group at Virginia Tech has responsibility for UCN transport for theLos Alamos experiment, the fast DAQ, and experimental coordination.The critical component of this system addressed by this proposal is thecoating for transporting polarized neutrons. We have shownpulsed-laser-deposition of diamond films is suitable. At VirginiaTech, an existing excimer laser has been re-commissioned to producesuitable films. A system for coating both the guide tubes and centraldecay tube of the spectrometer has been developed. The successfulcampaign to make suitably coated guides for polarized UCNs has animpact, not just to this experiment, but to planned future experimentsas well.