ＣＡＮＤＬＥＳによるＣａ４８の二重ベータ崩壊の研究

点击翻译按钮获取中文摘要

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.