| Co-Investigator(Kenkyū-buntansha) |
MORII Masahiro Faculty of Science, The University of Tokyo, assistant, 理学部, 助手 (50242095)
MICHELINI Aldo CERN(Conseil europeen pour la Recherche nucleaire), Professor, 素粒子実験部門, 主任研究員
SASAKI Makoto Faculty of Science, The University of Tokyo, assistant, 理学部, 助手 (40242094)
TSUKAMOTO Toshio Faculty of Science, The University of Tokyo, assistant, 理学部, 助手 (40217287)
MORI Toshinori Faculty of Science, The University of Tokyo, assistant, 理学部, 助手 (90220011)
KAWAGOE Kiyotomo Faculty of Science, The University of Tokyo, assistant, 理学部, 助手 (40183785)
MASHIMO Tetsuro Faculty of Science, The University of Tokyo, assistant, 理学部, 助手 (60181640)
KAWAMOTO Tatsuo Faculty of Science, The University of Tokyo, assistant, 理学部, 助手 (80153021)
TAKESHITA Tohru Faculty of Liberal Arts, The University of Shinshu, Associate professor, 教養部, 助教授 (70154995)
KOMAMIYA Sachio Faculty of Science, The University of Tokyo, Associate professor, 理学部, 助教授 (80126060)
TAKEDA Hiroshi Faculty of Science, The University of Kobe, Professor, 理学部, 教授 (30126114)
ORITO Shuji Graduate School of Science, The University of Tokyo, Professor, 大学院理学系研究科, 教授 (10092173)
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| Research Abstract |
The OPAL experiment, in which we are participating, is one of the four major experiments at the CERN large electron-positron collider(LEP), which started operation in 1989 to study e^+e^- reactions in the vicinity of the Z^0 boson resonance. The performance of LEP has been improving year after year. The OPAL experiment has been also very successful, and we collected 770k Z^0 events(peak only)in 1992 and 730k Z^0 events(peak and off-peak)in 1993, respectively. The number of Z^0 events from the beginning of the experiment now amounts to more than 2 million events. Not only the number of events is increased, but also the data quality is much improved with newly introduced detector elements as well as with better understanding of the detector.
The important results are listed below.
1. The Z^0 mass was determined with the best precision, by reducing the ambiguity of the beam energy from 20 MeV to 6 MeV. The standard model was tested with the measurements of Z^0 properties (total decay width, partial decay widths, forward-backward asymmetries of lepton-pair and quark pair productions). The top quark mass was confirmed to be about 150 GeV. The grand unified theory was tested with the measured coupling constants of the electroweak and strong interactions.
2. Two problems on gamma lepton were solved with the precise measurements of the branching fractions and the lifetime of gamma lepton.
3. A variety of bottom quark properties (Z^0 partial decay width, forward-backward asymmetry of pair production, lifetimes of bottomed mesons and baryons, and oscillation of neutral bottomed meson)were measured with outstandingly good precision.
4. The Higgs boson, elementary scalar particle in the standard model, is found to be heavier than 63 GeV. We obtained negative result on new particle with about 60 GeV mass, which had been suggested by the anomalous mass peak of two photons reported by the L3 group.
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