Precision double beta decay experiments with TITAN

点击翻译按钮获取中文摘要

Recent large-scale neutrino experiments like SNO and SuperK confirmed evidence for neutrino oscillations that can only occur if the neutrino is a massive particle. However, the nature of the neutrino involved in the process is still unclear (Dirac, Majorana), as well as the absolute neutrino masses and their ordering. Good access to these questions can be gained through neutrino-less double beta decay. If an uncontroversial detection of such a decay can be discovered, it is clear that lepton number conservation is broken, however it would be still unclear what mechanism leads to this form of decay. The search for such a decay is presently a hot topic of research and is being carried out or planned in a number of experiments, such as EXO, MAJORANA, GERDA, CUORE, COBRA, NEMO-III and SNO+. The 0beta decay rate depends on the neutrino mass but, also on a complex nuclear matrix element, making the extraction of the effective neutrino mass heavily dependent on the nuclear model. The present program is geared towards the measurement of the EC branching ratios (BR), one of the one-leg branches needed to test nuclear models and matrix element calculations. We propose such BR measurements using the TITAN ion trap facility at the TRIUMF ISAC facility. The measurements will be carried out by an international collaboration. It will make use of the existing TITAN system, together with a novel isobar separator system provided by the University of Giessen & GSI Darmstadt. This will ensure mono-isotopic, hence background free samples, can be stored in the EBIT Penning trap. During the decay, electrons will be confined by the magnetic field of the trap. Beta-detectors are provided by the collaboration partner TU Munich, and K-shell X-rays from EC will be detected by seven X-ray detectors located around the trap, provided by the University of Muenster. This new measurement scheme will be providing orders of magnitude background suppression and thus an ideal low-BR measurement environment. The experimental program is accepted by the TRIUMF experimental evaluation committee with high priority (E1066) and is ready for beam taking in 2009.