Grant-in-Aid for Specially Promoted Research.
|Research Institution||KYOTO UNIVERSITY|
NISHIKAWA Koichiro Kyoto Univ., Physics, Prof., 大学院・理学研究科, 教授 (60198439)
ISHII Iakanobu KEK, IPN, Res.Assoc, 素核研, 助手 (90134650)
OKUNO Hideki KEK IPN, Ass.Prof., 素核研, 助教授 (10013400)
OYAMA Yuichi KEK.IPN, Res.Assc, 素核研, 助手 (30213896)
NAKAMURA Kenzo KEK.IPN, Prof., 素核研, 教授 (10011735)
|Project Fiscal Year
1996 – 2000
Completed(Fiscal Year 2000)
|Budget Amount *help
¥288,000,000 (Direct Cost : ¥288,000,000)
Fiscal Year 2000 : ¥5,000,000 (Direct Cost : ¥5,000,000)
Fiscal Year 1999 : ¥5,000,000 (Direct Cost : ¥5,000,000)
Fiscal Year 1998 : ¥80,000,000 (Direct Cost : ¥80,000,000)
Fiscal Year 1997 : ¥127,000,000 (Direct Cost : ¥127,000,000)
Fiscal Year 1996 : ¥71,000,000 (Direct Cost : ¥71,000,000)
|Keywords||Neutrino mass / Neutrino oscillation / Accelerator neutrino / Long baseline / ニュートリノ質量 / ニュートリノ振動 / 加速器ニュートリノ / 長基線 / ニュートリノ / 素粒子 / レプトン / 標準模型 / 加速器ニュートリノ実験 / 陽子加速器|
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
principles 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