ＣＡＮＤＬＥＳによるＣａ４８の二重ベータ崩壊の研究

无中微子双衰变(0vββ)的实验观测将为解释物质主宰的宇宙提供轻子数非守恒的证据。对于我们的0vββ48Ca实验来说，对背景的清楚了解是最重要的部分。其中，2vββ背景估计是极其重要的，因为它是无法回避的。为了准确估计，48Ca的β衰变研究是必要的，因为我们使用的是大尺寸的CaF_2晶体，这可能是2Vββ谱的重要背景。我们建议达到β衰变半衰期48Ca对理论预测T1/2(β)=(1.1±0.6)×1021年的灵敏度。这是世界上首次将三重符合用于β衰变研究。为了获得较高的48Ca的β衰变灵敏度，用特殊的捕集树脂从1500LCaC12溶液中富集48Sc(β衰变产物)。(实验费用将主要集中在从大量CaCl2溶液中进行浓缩)。我们将使用32个CSI正弦仪进行三重符合测量，探测效率可以提高到5%。在第二年，我们将在神冈地下实验室进行实验，那里的宇宙射线背景极低。来自β衰变的预期事件为22.1次/年，而背景事件为6.4次/年。因此，β衰变的预期灵敏度为2.4×10~(21)年(95%C.L)。这种敏感度超过了理论预测的上限。这样，对于48Ca的2Vββ和0Vββ衰变，我们将得到更好的结果，统计误差更小。

Experimental observation of neutrinoless double decay(0vββ)will provides evidence on the lepton number non-conservation to explain the matter-dominated universe. Clear understanding of the background is the most important part for our 0vββ experiment with 48Ca. Among them, 2vββ background estimation is extremely important because it can never be avoided. For the precisely estimation, the β decay study of 48Ca is necessary because it could be substantial background for 2vββ spectrum since we use large size CaF2 crystals. We propose to reach sensitivity of β decay half lifetime of 48Ca to the theoretic predictionT1/2(β)=(1.1±0.6)×1021 yr. This is the first time to use triple coincidence for β decay study in the world. In order to reach higher sensitivity of β decay of 48Ca, 48Sc (the β decay product) will be enriched from 1500L CaC12 solution with ion exchange method by special capture resin. (The expenses of experiment will mainly concentrate on the enrichment from huge mount of CaCl2 solutions). We will use 32 CsI sintillators for the triple coincidence measurement and the detection efficiency can improve to 5%. In second year we will setup the experiment in Kamioka Underground Labrotory which has extremly low background from cosmic rays. Expecting events from β decay is 22.1/year compare with 6.4/year for background events. Thus the expecting sensitivity of β decay is 2.4×1021 yr (95%C. L) with 1 year measurement. That sensitivity is over the upper limit of theoretical prediction. Then we will get better result with less statistical error for 2vββand 0vββ decay of 48Ca.