2000 Fiscal Year Final Research Report Summary
Study of neutrino mass by long baseline neutrino oscillation experiment
| Project/Area Number |
08101002
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| Research Category |
Grant-in-Aid for Specially Promoted Research
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| Allocation Type | Single-year Grants |
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| Review Section |
Physics
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| Research Institution | KYOTO UNIVERSITY (1999-2000)
The High Energy Accelerator Research Organization (1997-1998)
The University of Tokyo (1996) |
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Principal Investigator |
NISHIKAWA Koichiro Kyoto Univ., Physics, Prof., 大学院・理学研究科, 教授 (60198439)
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| Co-Investigator(Kenkyū-buntansha) |
ISHII Iakanobu KEK, IPN, Res.Assoc, 素核研, 助手 (90134650)
OYAMA Yuichi KEK.IPN, Res.Assc, 素核研, 助手 (30213896)
NAKAMURA Kenzo KEK.IPN, Prof., 素核研, 教授 (10011735)
OKUNO Hideki KEK IPN, Ass.Prof., 素核研, 助教授 (10013400)
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| Project Period (FY) |
1996 – 2000
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| Keywords | Neutrino mass / Neutrino oscillation / Accelerator neutrino / Long baseline |
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| Research Abstract |
The project was approved in 1996 to design and construct the near detector system for the long baseline neutrino oscillation experiment. This experiment uses Super-Kamiokande as a far detector. Neutrinos, predominantly muon neutrinos, are produced KEK proton synchrotron. The distance from KEK and Super-Kamiokande is 250km. The purpose is to test whether muon-neutrinos changes to other type of neutrinos in 250km travel to verify non-zero neutrino mass and lepton mixing. The events in the Super-Kamiokande are compared with those in near detector. In 1998 neutrino beam line and near detector construction were completed. In February 1999, we observed first neutrino event in near detector.
In June 1999, we identified first neutrino event in Super-Kamiokande. This is the first time in the world that man-made elementary particles traveled earth-scale distance and detected.
Until June 2000, we took data for 100 actual days. The data taking resumed in January 2001.
We have established that the pri
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nciples of long baseline neutrino oscillation experiment works and obtained the following results at its point.
(1) The direcdon of neutrino beam can be controlled and monitored within 1 mrad. during the entire period of the data taking. This directional precision is more than enough to predict the neutrino beam at 250km away.
(2) We can identify neutrino events in Super-Kamiokande with GPS time stamp. The backgrounds due to atmospheric neutrinos etc. are negligible at the level of 10^<-4>-10^<-5>.
(3) The events rate in the near detector system is about 3000/day. This rate is enough to monitor the stability of the neutrino beam.
(4) The result obtained during first 100 days of data taking is that we observed 27 events in Super-Kamiokande while we predict 40 events with an assumption of no oscillation. This equivalent to the statement that neutrino oscillation exists with 90% probability.
This result was reported at NEUTRINO-2000 in June and ICHEP (International Conference of High Energy Physics) in August 2000 and other conferences or workshops. With more data taking, we can firmly establish neutrino oscillation that is the proof that neutrinos are massive and lepton number is violated in nature. Less
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