Precision double beta decay experiments with TITAN

最近的大规模中微子实验，如SNO和Superk证实了中微子振荡的证据，只有在中微子是大质量粒子的情况下才能发生中微子振荡。然而，参与这一过程的中微子的性质仍然不清楚(狄拉克、马约拉纳)，以及中微子的绝对质量和它们的顺序。通过无中微子的双β衰变可以很好地解决这些问题。如果能够发现这种衰变的无争议的探测，很明显轻子数守恒被打破了，然而，什么机制导致了这种形式的衰变仍然不清楚。寻找这样的衰变目前是一个热门的研究课题，并正在进行或计划在一些实验中进行，如EXO，Majorana，Gerda，CuORE，COBRA，NEMO-III和SnO+。0β衰减率不仅取决于中微子的质量，而且还取决于复杂的核矩阵元素，这使得有效中微子质量的提取严重依赖于核模型。目前的程序是为了测量EC分支比(BR)，这是测试核模型和矩阵元素计算所需的单支路之一。我们建议使用TRIUMF ISAC设施的泰坦离子陷阱设施进行这样的BR测量。测量将由国际合作进行。它将利用现有的泰坦系统，以及吉森大学和达姆施塔特大学提供的新型等压线分离器系统。这将确保单同位素，因此无背景样品，可以储存在EBIT Penning陷阱中。在衰变过程中，电子将受到陷阱磁场的限制。贝塔探测器由合作伙伴德国慕尼黑理工学院提供，EC的K壳层X射线将由明斯特大学提供的位于陷阱周围的七个X射线探测器探测。这种新的测量方案将提供数量级的背景抑制，从而提供理想的低BR测量环境。该实验计划被TRIUMF实验评估委员会优先接受(E1066)，并准备在2009年进行束流测量。

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.