Messung des gebundenen Betazerfalls freier Neutronen

自由中子的束缚β衰变的测量

• 批准号: 167645759
• 负责人: Professor Dr. Stephan Paul
• 金额: --
• 依托单位: Arbeitsgruppe Hadronenstruktur und Fundamentale Symmetrien
• 依托单位国家: 德国
• 项目类别: Priority Programmes
• 财政年份: 2010
• 资助国家: 德国
• 起止时间: 2009-12-31 至 2013-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/167645759?language=en
• 关键词: Messung; des; gebundenen; Betazerfalls; freier

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.

该项目旨在探测中子的一个新的衰变分支，即预计约占标准衰变的4（10-6）的二体衰变n→H+ve。这种衰变有可能提供一个新的访问弱相互作用的耦合方案的测量，并构成直接测量β衰变的ve。弱相互作用的洛伦兹结构可以通过测量出射氢的不同超精细态的布居来检验，出射氢的超精细态也可以作为测量出射氢的螺旋度的镜子。（慕尼黑的FRMII），并随后检测它们。在束管内与堆芯相切的中子衰变中，以随机（不可重复）方式出现的中性氢原子的探测是通过它们处于2s量子态（约占该衰变分支中所有氢原子的10%）来确定的，从2s量子态中，它们要么被猝灭发射特征莱曼-α光子，要么被激光技术共振电离。背景氢的鉴别（热光谱和连续光谱）是通过磁光谱仪作用于电离氢原子，选择单能氢原子来完成的。该项目分为两个部分，第一部分是首次探测这种衰变通道，随后证明这种光谱测量的原理，第二部分将解决出现的2s氢原子的超精细态的精确测量。只有第一部分是本申请的主题。对于第二部分，激光系统将由Th.慕尼黑的马克斯-普朗克量子光学研究所（MPQ）的Udem说。在这里，我们使用现有的激光器（氩离子激光器和钛safire激光器）和开发工作将集中在谐振器和完整的设置。第一阶段的实验将在光束管SR 6在FRMII（或交替在ILL在格勒诺布尔）进行。氢原子将通过轴向（w.r.t.向飞行方向）的电场，并探测到H（2s）态。在第一个实验中，它们被光传感器检测到的发射光猝灭。将确定与标准衰变相比的分支比。第二个实验是氢原子通过自旋滤波器，在这个滤波器中，所有不需要的HFS态H（2s）被淬灭为H（1 s），并对产生的氢“束”进行动量分析，对残存的H（2s）态的探测选择性约为10：1。最后一个实验（第二阶段）将预见残存的H（2s）态的多普勒校正共振电离，这是根据其在自旋滤波器中的HFS态选择的。质子随后被检测和识别。最终的准确性将在很大程度上取决于所获得的效率和今天未知的背景。在理想条件下，Hve可以在一个月的测量时间内被确定为10-3的精度。这一阶段的物理测量将在2013年之后进行。