Messung von Kern-Matrixelementen im doppelten Beta-Zerfall

• Applicant: Professor Dr. Dieter Frekers
• Subject Area: Nuclear and Elementary Particle Physics, Quantum Mechanics, Relativity, Fields
• Term: from 2010 to 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 127016317

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.

• DFG Programme: Research Grants
• International Connection: Canada, Japan, USA
• Major Instrumentation: Si(Li)-Detektorsystem
• Instrumentation Group: 5810 Photoelektrische Wandler, Photoelemente, Solarzellen, Photovoltaik
• Participating Persons: Professor Dr. Jens Dilling; Professor Dr. Hiroyasu Ejiri; Professor Dr. Remco Zegers