電子・陽電子衝突装置LEP-IIでのOPAL測定器による素粒子の研究

1998 年度 実績報告書

• 研究課題/領域番号: 09044060
• 研究機関: 東京大学
• 研究代表者: 小林 富雄 東京大学, 素粒子物理国際研究センター, 教授 (50126059)
• 研究分担者: 真下 哲郎 東京大学, 素粒子物理国際研究センター, 助手 (60181640) ; 森 俊則 東京大学, 素粒子物理国際研究センター, 助教授 (90220011) ; 川本 辰男 東京大学, 素粒子物理国際研究センター, 助教授 (80153021) ; 駒宮 幸男 東京大学, 素粒子物理国際研究センター, 教授 (80126060) ; 折戸 周治 東京大学, 大学院・理学系研究科, 教授 (10092173)
• キーワード: LEP / LEP-II / OPAL / 鉛ガラスカロリメター / 標準理論 / Wボソン / ヒッグス粒子 / 超対称性理論

研究概要

平成10年度、LEPはエネルギーを更に増強し、衝突エネルギー189GeVで実験を行った。春から秋にかけての運転期間を通じ安定に効率良く運転さて、前年度に比べて約3倍の積分ルミノシティーを達成した。OPAL測定器は順調に稼働し、東京大学が建設した最も重要な構成要素の一つである鉛ガラスカロリメターも高性能を維持し、質の高いデータを高い効率で収集した。
衝突エネルギーの増加は、ヒッグス粒子や超対称性粒子など重い(エネルギーが十分ないと生成できない)新粒子発見の可能性を意味する。また、この大量のデータを基に、W粒子質量等の精密測定は更に精度が向上した。このデータを最大に生かし、測定精度や新粒子探索の感度を上げるため、測定器の性能チェックやキャリブレーションを詳細に行うとともに、物理解析方法を改良し、また新しい角度からの解析を開発してきた。主な成果としては:
(1) 約3000のW粒子対発生事象を記録した。これは前年度までに収集された総数の約3倍に相当する。LEPでのW粒子の質量測定精度は陽子反陽子衝突実験からの結果を上回るものになってきた。いよいよ精密測定の領域に入ってきたので、系統誤差の詳細な評価が一段と重要になる。
(2) 標準理論で期待される各種の反応過程を幅広く解析し、新しいエネルギー領域で理論をテストした。標準理論からのずれを生むかもしれない新物理の可能性について制限をつけた。
(3) 標準理論のミッシングリンクであるヒッグス粒子の探索を行い、その質量が約91GeVより重いという結果を得た。
(4) 標準理論を越える理論として最も有力な超対称性理論が予言する新粒子群を系統的に探索し、その未知のパラメータについてより厳しい制限を得た。
これらの結果は逐次国際会議等で報告され学術専門誌に発表している。

研究成果

• [文献書誌] The OPAL Collaboration: "Seach for Anomalous Production of Di-lepton Events with Missing Transverse Momentum in e^+e^- Collisions at √<S>=161 and 172 Gev" Euro.Phys.Journal. C4. 47-74 (1998)
• [文献書誌] The OPAL Collaboration: "Measurement of Triple Gauge Boson Coupligs from W^+W^- Production at √<S>= 172 GeV" Euro.Phys.Journal. C2. 607-625 (1998)
• [文献書誌] The OPAL Collaboration: "Seach for Anomalous Production of Photonic Events with Missing Energy in e^+e^- Collisions at √<S>=130-172 GeV" Euro.Phys.Journal. C2. 607-625 (1998)
• [文献書誌] The OPAL Collaboration: "Search for The Bc Meson in Hadronic Zo Decays" Phys.Lett.B420. 157-168 (1998)
• [文献書誌] The OPAL Collaboration: "Measurement of the one-prong Hadronic Tau Branching Ratios at LEP" Euro.phys.Journal. C4. 193-206 (1998)
• [文献書誌] The OPAL Collaboration: "Measurements of the B^o_S and Λ^o_b Lifetimes" Phys.Lett.B426. 161-179 (1998)
• [文献書誌] The OPAL Collaboration: "Search for charged Higgs bosons in e^+e^- collisions at √<S>=130-172 GeV" Phys.Lett.B426. 180-192 (1998)
• [文献書誌] The OPAL Collaboration: "Determination of the Production Rate of D^<*0> Mesons and of the Ratio V/(V+P) in Z^o→cc Decays" Euro.Phys.Journal. C5. 1-17 (1998)
• [文献書誌] The OPAL Collaboration: "Production of fo(980),f_2(1270) and φ(1020) in Hadronic Z^o Decay" Euro.Phys.Journal. C4. 19-28 (1998)
• [文献書誌] The OPAL Collaboration: "Investigation of CP Violation in B^o→J/φK^o_s Decays at LEP" Euro.Phys.Journal. C5. 379-388 (1998)
• [文献書誌] 4 LEP experiments: "Combination of Preliminary Electroweak Measurements and Constraints on the Standard Modei" CERN-PPE/97-154.
• [文献書誌] The OPAL Collaboration: "Search for an Excess in the Production of Four-Jet Events from e^+e^- Collisions at √<S>=130-184 GeV" Phys.Lett.B429. 399-413 (1998)
• [文献書誌] The OPAL Collaboration: "A Search for Neutral Higgs Bosons in the MSSM and Hodels with Two Scalar Field Doublets" Euro.Phys.Journal. C5. 19-40 (1998)
• [文献書誌] The OPAL Collaboration: "An Upper Limit on the Anomalous Magnetic Moment of the tou lepton" Phys.Lett.B431. 188-198 (1998)
• [文献書誌] The OPAL Collaboration: "Search for Stable and Long-lived Massive Charged Particles in an Excess in e^+e^- Collisions at √<S>=130-183 GeV" Phys.Lett.B433. 195-208 (1998)
• [文献書誌] The OPAL Collaboration: "Photon and Light Meson Production in Hadronic Z° Decays" Euro.Phys.Journal. C5. 411-437 (1998)
• [文献書誌] The LEP Working Group for Higgs Boson Searches: "Lower Bound for the Standard Model Higgs Boson Mass from Combining the Results of the four LEP Experiments" CERN-EP/98-046.
• [文献書誌] The OPAL Collaboration: "An Upper Limit for the tau-neutrino Mass from T→5π^<【plus-minus】> V_T Decays" Euro.Phys.Journal. C5. 229-237 (1998)
• [文献書誌] The OPAL Collaboration: "Bose-Einstein Correlations of Three Charged Pions in Hadranic Z^o Decays" Euro.Phys.Journal. C5. 239-248 (1998)
• [文献書誌] The OPAL Collaboration: "Inclusive Production of Charged Hadrons and K^o_s Mesons in Photon-Photon Collisions" Euro.Phys.Journal. C6. 253-264 (1999)
• [文献書誌] The OPAL Collaboration: "Multi-photon production in e^+e^- Collisions at √<S>=183 GeV" Phys.Lett.B438. 379-390 (1998)
• [文献書誌] The OPAL Collaboration: "Search for Higgs Bosons and New Particres Decaying into Two Photons at √<S>=183 GeV" Phys.Lett.B437. 218-230 (1998)
• [文献書誌] The OPAL Collaboration: "Tests of the Standard Model and Constraints on New Physics from Measurements of Fexmion-pair Production at 183 GeV at LEP" Euro.Phys.Journal. C6. 1-18 (1998)
• [文献書誌] The OPAL Collaboration: "Production of Xc_2 Mesons in Photon-Photon Collisions at LEP" Phys.Lett.B439. 197-208 (1998)
• [文献書誌] The OPAL Collaboration: "Search for Scalar Top and Scalar Bottom Quarks at ECM=183 GeV at LEP" Euro.Phys.Journal. C6. 225-238 (1999)
• [文献書誌] The OPAL Collaboration: "First Measurement of Z/γ^* Production in Compton Scattering of Quasi-real Photons" Phys.Lett.B438. 391-404 (1998)
• [文献書誌] The OPAL Collaboration: "Measurement of the Longitudinal Cross-Section using the Direction of the Thrust Axis in H〓nic Events at LEP" Phys.Lett.B440. 393-402 (1998)
• [文献書誌] The OPAL Collaboration: "Search for Acoplanar Lepton Pair Events in e^+e^- Annihilation at √<S>=161,172,and 183 GeV" CERN-EP/98-122 Euro.Phys.Journal. (submitted to).
• [文献書誌] The OPAL Collaboration: "Measurement of the Average Polarization of b Bcuryons in Hadronic Z° Decay" Phys.Lett.B444. 539-554 (1998)
• [文献書誌] The OPAL Collaboration: "Search for Chargino and Neutralino Production at √<S>=181-184 GeV at LEP" CERN-EP/98-136 Euro.Phys.Journal. (submitted to).
• [文献書誌] The OPAL Collaboration: "A Measurement of Rb using a Double Tagging Method" CERN-EP/98-137 Euro.Phys.Journal. (submitted to).
• [文献書誌] The OPAL Collaboration: "Search for Anomalous Photonic Events with Missing Errergy in e^+e^- collisions at √<S>=130,136 and 183 GeV" CERN-EP/98-143 Euro.Phys.Journal. (submitted to).
• [文献書誌] The OPAL Collaboration: "Measurement of the Semilieptonic Brarching Ratio of Charm Hadrons produced in Z°→cc Decays" CERN-EP/98-146 Euro.Phys.Journal. (submitted to).
• [文献書誌] The OPAL Collaboration: "W^+W^- production and triple gauge boson couplings at LEP energies up to 183 GeV" CERN-EP/98-167 Euro.Phys.Journal. (submitted to).
• [文献書誌] The OPAL Collaboration: "Search for Higgs Bosons in e^+e^- Coollisions at 183 GeV" CERN-EP/98-173 Euro.Phys.Journal. (submitted to).
• [文献書誌] The OPAL Collaboration: "Bose-Einstein Correlations in e^+e^-→ W^+W^- at 172 and 183 GeV" CERN-EP/98-174 Euro.Phys.Journal. (submitted to).
• [文献書誌] The OPAL Collaboration: "Search for Baryon and Lepton Number Violating Z° Decays" CERN-EP/98-194 Phys.Lett.(submitted to).
• [文献書誌] The OPAL Collaboration: "A Measurement of the T→e nu nu bar Branching Ratio" CERN-EP/98-175 Phys.Lett.(submitted to).
• [文献書誌] The OPAL Collaboration: "A Measurement of the Product Branching Batio f(b→Λ_b),BR(Λb→ΛX) in Z^o Decays" CERN-EP/98-186 Euro.Phys.Journal. (submitted to).
• [文献書誌] The OPAL Collaboration: "Measurement of the B^+ and B^o Lifetimes and Search for CP(T) Violation using Reconstructed Seuonda Vertices" CERN-EP/98-195 Euro.Phys.Journal. (submitted to).
• [文献書誌] The OPAL Collaboration: "Colour reconnection studies in e^+e^-→w^+w^- at √<S>=183 GeV" CERN-EP/98-196 Phys.Lett.(submitted to).
• [文献書誌] The OPAL Collaboration: "Measurement of the W Mass and Width in e^+e^- Collisions at 183 GeV" CERN-EP/98-197 Phys.Lett.(submitted to).
• [文献書誌] The OPAL Collaboration: "Searches for R-Parity Violating Decays of Gauginos at 183 GeV at LEP" CERN-EP/98-203 Euro.Phys.Journal. (submitted to).
• [文献書誌] The OPAL Collaboration: "Intermittency and Correlations in Hadronic Z^o Decays" CERN-EP/99-009 Euro.Phys.Journal. (submitted to).
• [文献書誌] The OPAL Collaboration: "Measurements of the QED Structure of the Photon" CERN-EP/99-010 Euro.Phys.Journal. (submitted to).
• [文献書誌] 4 LEP experiments: "A Combination of Preliminary Electroweak Measurements and Constraints on the Standard Model" CERN-EP/99-015.
• [文献書誌] The OPAL Collaboration: "Experimental Properties of Gluon and Quark Jets from a Point Source" CERN-EP/99-028 Euro.Phys.Journal. (submitted to).
• [文献書誌] The OPAL Collaboration: "Search for Scalar Top and Scalar Bottom Quartcs at ECM = 189 GeV at LEP" 26th February 1999,Phys.Lett.(submitted to).