| Budget Amount *help |
¥3,900,000 (Direct Cost: ¥3,900,000)
Fiscal Year 1999: ¥600,000 (Direct Cost: ¥600,000)
Fiscal Year 1998: ¥3,300,000 (Direct Cost: ¥3,300,000)
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| Research Abstract |
In order to establish the solar neutrino oscillation, we must measure the energy spectrum of 8B solar neutrinos below 6.5 MeV precisely. However there are a huge background in those energy region. The purpose of this project is that the investigate the characteristics of those background and development of software which excludes them. For radio-isotope backgrounds, we could measure ィイD1222ィエD1Rn by using high sensitive radon detector, and obtained as 1.4mBq/mィイD13ィエD1 for input purified water. On the other hands, we have seen background clustered around the bottom of Super-Kamiokande detector in the data. Those background had same life time as ィイD1222ィエD1Rn, however, the measured concentration was 4mBq/mィイD13ィエD1. It was not consistent with one observed by the radon detector. Using Monte Carlo simulation of ィイD1214ィエD1Bi, which is daughter nuclei of ィイD1222ィエD1Rn, and ィイD1208ィエD1Tl for thorium series, I found about 50% contamination of ィイD1208ィエD1Tl in the background. Even though we e
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xtract the radio-isotope Background completely, almost 90% of background still remains. Most of those background consists of an accidental overlapped events, because they had a unique characteristics of their low goodness for the vertex reconstruction and almost same values around their vertex position. Using this character. I developed the software to exclude those event from data. Applying for real data from May 1997, about 90% of background without radio-isotope could be excluded. The efficiency of solar neutrino signal keeps 90%, and the systematic error should be less 2%. Now we are processing for whole data-set until October 1999, and the preliminary results were obtained by 0.48 and 0.43 times the expected flux from standard solar model for 5.5-6.0 MeV and 6.0-6.5MeV, respectively. From this results, there seems to be flat spectrum then there also exist the probability to exclude the small angle solution. Of course, still we need more statistics of data, however, this project could show the ability of constraint for allowed neutrino oscillation parameters by all 4 solar neutrino experiments. Less
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