| Project/Area Number |
05452024
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| Research Category |
Grant-in-Aid for General Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Research Field |
素粒子・核・宇宙線
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| Research Institution | University of Tokyo |
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Principal Investigator |
SUGIMOTO Shojiro Institute for Nuclear Study, Univ.of Tokyo, professor, 原子核研究所, 教授 (20044753)
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| Co-Investigator(Kenkyū-buntansha) |
SHINKAWA Takao National Laboratory for High Energy Physics, research associate, 助手 (70171064)
KOMATSUBARA Takeshi Institute for Nuclear Study, Univ.of Tokyo, research associate, 原子核研究所, 助手 (30242168)
UKAI Kumataro Institute for Nuclear Study, Univ.of Tokyo, associate professor, 原子核研究所, 助教授 (40013411)
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| Project Period (FY) |
1993 – 1995
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| Project Status |
Completed (Fiscal Year 1995)
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| Budget Amount *help |
¥7,200,000 (Direct Cost: ¥7,200,000)
Fiscal Year 1995: ¥1,400,000 (Direct Cost: ¥1,400,000)
Fiscal Year 1994: ¥1,900,000 (Direct Cost: ¥1,900,000)
Fiscal Year 1993: ¥3,900,000 (Direct Cost: ¥3,900,000)
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| Keywords | K meson decay / Pulse shape analysis / Gamma-ray detection / High intensity kaon beam / K中間子 / 稀崩壊 / K中間子稀崩壊 / フォトン・ベトー |
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| Research Abstract |
The rare kaon decay KAPPA<@D1+@>D1 *pi<@D1+@>D1nu<@D4nu@>D4, a flavor changing neutral current process, is strongly suppressed by the Glashow-Iliopoulos-Miani Mechanism. The branching ratio, which mainly depends on the Kobayashi-Maskawa matrix element |Vtd|, is predicted to be (1.1(]SY.+-。[)0.4)*10<@D1-10@>D1 by the Standard Model, while the present upper limit is 2.4*10<@D1-9@>D1 (90% c.l.). In order to improve this experimental sensitivity, we upgraded our detector system and developed various methods for background rejection, namely rejection of pi<@D1+@>D1pi<@D10@>D1, mu<@D1+@>D1nu, mu<@D1+@>D1nu gamma decay events.
This project aimed to develop a fast pulse separation method, by which occurrence of background event just before or just after triggering can be reliably identified even if two pulses are piled up. Analog output pulses from each module in the E787 gamma veto detector were recorded with a high speed transient digitizer and analyzed through on-line and off-line program codes. Since precise time and energy information is indispensable to obtain a good veto efficiency for gamma-ray and a low accidental veto rate, we carefully investigated pulse shapes of outputs from all channels of the gamma veto detector and tuned the analysis code.
In the 1995 physics run at BNL,we took data written on 4200 tapes and studied detector response to the background process, KAPPA^+ *pi^+pi^0, as well as data analysis for KAPPA^+ *pi^+nu^^<nu>. We found that a time resolution of better than 1ns was obtained for low-energy photons down to 10 MeV.The accidental event rate at 1.2*10^6 (kaons stopping on our target)/pulse was about 5%. We obtained a rejection factor of 1*10^6 to KAPPA^+ *pi^+pi^0 decay (with 25% acceptance loss) through the analysis code which we developed in this project
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