Messung von Kern-Matrixelementen im doppelten Beta-Zerfall

双β衰变是目前实验亚原子研究的前沿。这是因为对无中微子的Ovße衰变模式的观测立即发出了超越标准模型的物理信号，因为它意味着中微子是一种马约拉纳粒子。然而，当试图从一个特定的衰变中提取中微子的质量时，核物理的知识贫乏构成了一个几乎尴尬的局面。这所需要的核基质元素似乎都没有坚实的实验基础。本项目从不同的方面解决这一问题，并将以不同的强度进行所建议的实验：1）主要部分将是使用TRIUMF放射性束设施的新离子阱设施TITAN/EBIT测量β衰变中奇-奇中间核的电子捕获（EC）分支比。EC的分支比，这是知之甚少或根本不知道，是很重要的评估核矩阵元素的两个，2 V和OV衰变模式。该实验技术新颖，在灵敏度和背景上均超过传统技术几个数量级。2)上述测量将通过（d，<$He）、（<$He，t）和（t，<$He）电荷交换反应进行补充。虽然格罗宁根KVI的（d，²He）计划已基本完成，但（<$He，t）和（t，<$He）实验将在大坂RCNP和密歇根州立大学NSCL进行。所有上述设施（KVI、RCNP、TRIUMF）在许多重要方面都是独一无二的。本项目由国际合作（德国、加拿大、美国、日本）实施。我们预计，通过开展联网活动，这种国际合作将得到加强。这些补充活动已经开始（在这里，通过其“前沿实验室”计划与大坂大学合作，并与明斯特大学签订合作协议）。各种设施，如RCNP，TRIUMF，NSCL（以及过去的KVI），都将目前协调一致的国际努力视为其实验计划的高度优先事项，以解决双β衰变矩阵元素。已提交给各方案咨询委员会的各项建议无一例外都得到了高度优先的评价。

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.