Messung von Kern-Matrixelementen im doppelten Beta-Zerfall

双β （ß）衰变目前处于亚原子实验研究的前沿。这是因为对无中微子的ov ßß衰变模式的观察立即标志着物理学超越了标准模型，因为它意味着中微子是马约拉纳粒子。然而，当试图从一个特定的衰变中提取中微子的质量时，核物理知识的贫乏构成了一个几乎令人尴尬的局面。为此所需的核基质元素似乎都没有坚实的实验基础。本项目从不同的角度解决了这个问题，提出的实验将以不同的强度进行：1)主要部分将是利用TRIUMF放射性束流设施的新离子阱设施TITAN/EBIT测量ßß衰变中奇-奇中间核的电子捕获（EC）分支比。EC分支比对于评估2v和ov衰变模式的核矩阵元素是很重要的，尽管人们对它知之甚少或根本不知道。该实验技术新颖，在灵敏度和背景上都比传统技术高出几个数量级。2)上述测量将由（d，²He），（³He,t）和（t，³He）电荷交换反应补充。格罗宁根KVI的（d，²He）项目已经基本完成，（³He,t）和（t，³He）实验将在大阪RCNP和密歇根州立大学NSCL进行。所有提到的设施（KVI， RCNP， TRIUMF）在许多重要方面都是独一无二的。目前的项目是由国际合作（德国、加拿大、美国、日本）进行的。我们预见，这种国际合作将通过开展联网活动而得到加强。这些补充活动已经开始（在这里，与大阪大学通过其“FrontierLab”计划和与大学<s:1> nster的合作协议）。各种设施，如RCNP， TRIUMF， NSCL（以及过去的KVI）认为，目前协调一致的国际努力解决双β衰变矩阵元素是他们实验计划的重中之重。提交给各自的项目咨询委员会（PAC’s）的各种提案无一例外地获得了高优先级。

Double-beta (ßß)-decay is presently at the forefront of experimental sub-atomic research. This is because the observation of the neutrinoless Ovßß-decay mode immediately signals physics beyond the Standard Model, as it implies the neutrino to be a Majorana particle. However, when attempting to extract the mass of the neutrino from a particular decay, the poor knowledge of the nuclear physics constitutes an almost embarrassing situation. None of the nuclear matrix elements needed for this seems to have a solid experimental foundation. The present project addresses this issue from different sides, and the experiments proposed will be pursued with different intensities: 1) The major part will be the measurement of the electron capture (EC) branching ratios for the odd-odd intermediate nuclei in ßß-decay using the new ion trap facility TITAN/EBIT at the TRIUMF radioactive beam facility. The EC branching ratios, which are either poorly known or not known at all, are important for evaluating the nuclear matrix elements for both, the 2v and the Ov-decay mode. The experimental technique is novel and surpasses the traditional techniques by several orders of magnitude in sensitivity and backgrounds. 2) The above measurements will be complemented by (d,²He), (³He,t) and (t, ³He) charge-exchange reactions. Whereas the (d, ²He) program at KVI, Groningen, has largely been completed, the (³He,t) and (t,³He) experiments will be done at RCNP, Osaka, and NSCL, Michigan State University. All of the mentioned facilities (KVI, RCNP, TRIUMF) are unique in many important respects. The present project is pursued by an international collaboration (Germany, Canada, USA, Japan). We foresee that this international collaboration will be strengthened through the initiation of networking activities. These supplementing activities have already commenced (here; with the University of Osaka through its "FrontierLab" Program and a Cooperation Agreement with the University Münster). The various facilities, like RCNP, TRIUMF, NSCL (and in the past KVI) regard the present concerted and international effort to address the double-beta decay matrix elements a high priority of their experimental programs. The various proposals, which have been submitted to the respective Program Advisory Committees (PAC's), have received without exception a high priority rating.