Messung des gebundenen Betazerfalls freier Neutronen

该项目旨在探测中子的一个新的衰变分支，即两体衰变n→H+ve，预计约占标准衰变的4（10-6）。这种衰变有可能为弱相互作用耦合方案的测量提供一种新的途径，并构成对β衰变中的ve的直接测量。弱相互作用的洛伦兹结构可以通过测量出现的氢的不同超精细态的人口来测试，这也可以作为测量发射的螺旋度的镜子。根据参考文献9中概述的想法，我们想用光谱分析从中子源（慕尼黑FRMII）反应堆堆芯中出现的动能约为326 eV的氢原子，并随后检测它们。探测到中性氢原子以随机（不可触发）的方式出现在与核心切向的束流管内的中子衰变中，通过它们处于2s量子态（这些原子的数量约占该衰变分支中所有氢原子的10%）来识别，它们要么被淬灭，发射出特征的莱曼α光子，要么被激光技术共振电离。利用磁谱仪作用于电离氢原子，选择单能氢原子，对背景氢（热谱和连续谱）进行判别。该项目分为两部分，第一部分是首次探测到这种衰变通道，并随后证明这种光谱测量的原理，第二部分将解决新兴2s氢原子超精细状态的精确测量。只有第一部分是本应用程序的主题。第二部分是激光系统的开发。Udem来自慕尼黑马克斯普朗克量子光学研究所（MPQ）。在这里，我们使用现有的激光器（氩离子激光器和钛安全激光器），开发工作将集中在谐振器和完整的设置上。本实验的第一阶段将在FRMII（或格勒诺布尔的ILL）的SR6束流管中进行。氢原子将通过一个轴向（相对于飞行方向）电场在核心下游约10米处，H（2s）态被检测到。在第一个实验中，它们被光传感器探测到的发射光淬灭。将确定与标准衰减相比的分支比。在第二个实验中，氢原子将通过一个自旋过滤器，在这个过滤器中，所有不需要的H（2s）的hfs态都被淬灭为H(1s)，产生的氢“束”被动量分析，用于检测剩余的H（2s）态的选择性约为10:1。最后的实验（第二阶段）将预测幸存的H（2s）态的多普勒校正共振电离，H（2s）态是根据其在自旋滤波器中的HFS状态选择的。随后检测和识别质子。最终的准确性将在很大程度上取决于所获得的效率和目前尚不清楚的背景。在理想的条件下，Hve可以在一个月的测量时间内确定到10-3的精度。这一阶段的物理测量将在2013年之后进行。

The project aims at the detection of a new decay branch of the neutron, namely the two-body decay n→H+ve expected to make up about 4(10-6 of the standard decay. This decay has the potential to offer a new access to the measurement of the coupling scheme of weak interaction and constitutes a direct measurement of the ve in beta decays. The Lorentz structure of weak interaction can be tested by measuring the population of the different hyperfine states of the emerging hydrogen which also serves as a mirror for the measurement of the helicity of the emitted ve Following the ideas outlined in reference 9 we want to spectroscopically analyse hydrogen atoms emerging with a kinetic energy of about 326 eV from the reactor core of a neutron source (FRMII in Munich) and subsequently detect them as such. Detection of neutral hydrogen atoms emerging in a random (untriggerable) way from neutron decays within a beam tube tangential to the core are identified by their being in the 2s quantum state (population of those is about 10% of all hydrogen atoms from this decay branch) from which they are either quenched emitting characteristic Lyman-α photons or resonance ionized by laser techniques. The discrimination against background hydrogen (thermal and continuous spectrum) is done by means of magnetic spectrometer acting on the ionized hydrogen atoms selecting the mono-energetic ones.The project is split into two parts, the first one being the first detection of this decay channel with subsequent proof of principle of such a spectroscopic measurement, the second part will address the precision measurement of the hyperfine states of the emerging 2s hydrogen atoms. Only the first part is subject of this application. For the second part the laser system will be developed by Th. Udem from the Max-Planck Institute for Quantum Optics (MPQ) in Munich. Here we use existing lasers (argon-ion laser and titanium-safire laser) and development work will focus on resonators and the complete set-up.Stage one of this experiment will be conducted at the beam tube SR6 at the FRMII (or alter-natively at ILL in Grenoble). Hydrogen atoms will pass an axial (w.r.t. to the direction of flight) electric field about 10 m downstream of the core and the H(2s) states are detected. In a first experiment they are quenched with the emitted light being detected by a photo sensor. The branching ratio as compared to the standard decay will be determined. For a second ex-periment hydrogen atoms will pass a spin filter in which all unwanted HFS-states of H(2s) are quenched to H(1s) and the resulting hydrogen ‘beam’ is momentum analyzed with a selectiv-ity for detection of the surviving H(2s) states of about 10:1.The final experiment (2nd stage) will foresee Doppler corrected resonant ionization of the surviving H(2s) state, which has been selected according to its HFS state in a spin filter. Protons are subsequently detected and identified. The final accuracy will depend much on the efficiencies obtained and on backgrounds not known today. Under ideal conditions Hve can be determined to a precision of 10-3 within one month of measuring time. The physics measurements for this stage will only take place after 2013.