Grant-in-Aid International Scientific Research
|Research Institution||The University of Tokyo|
YAMADA Sakue University of Tokyo, Institute for Nuclear Study, Professor, 原子核研究所, 教授 (70011658)
WOLF Guenter DESY, Prof., 主任研究員
SCIULLI Fran コロンビア大学, 教授
CASHMORE Rog オックスフォード大学, 教授
椎野 二男 東京大学, 原子核研究所, 助手 (20092231)
久世 正弘 東京大学, 原子核研究所, 助手 (00225153)
石井 孝信 東京大学, 原子核研究所, 助手 (90134650)
鶴貝 達政 明治学院大, 一般教育部, 専任講師 (50267366)
TOKUSHUKU Katsuo Univ. Tokyo, INS, Ass. Prof., 原子核研究所, 助教授 (80207547)
HAMATSU Ryosuke Tokyo Metropolitan Univ., Dept. of Phys., Ass. Prof., 理学部, 助教授 (20087092)
HIROSE Tachishige Tokyo Metropolitan Univ., Dept. of Phys., Prof., 理学部, 教授 (70087162)
CASHMORE Roger Univ. Oxford, Prof., 教授
|Project Fiscal Year
1996 – 1996
Completed(Fiscal Year 1996)
|Budget Amount *help
¥9,000,000 (Direct Cost : ¥9,000,000)
Fiscal Year 1996 : ¥9,000,000 (Direct Cost : ¥9,000,000)
|Keywords||electron-proton collision / electroweak interaction / standard model / quantum chromodynamics / neutral current interaction / leptoquarks / proton structure functions / charged current interaction / 電子陽子衝突 / 電弱相互作用 / 標準模型 / 量子色力学 / 高いQ^2中性流反応 / レプトクォーク / 陽子構造関数 / 荷電流反応 / HERA / ZEUS / W、Z粒子|
We studied the electroweak interaction in electron-proton collisions by using a multi purpose detector built in an international collaboration (ZEUS) at DESY in Germany. The unique collider HERA provides high-energy electron-proton collison, whose maximum four momentum transfer squared (QィイD12ィエD1) reaches 10ィイD15ィエD1 GeVィイD12ィエD1. By investigating the neutral current (NC) interaction which is mediated by the photon and/or the Z boson as well as the charged current (CC) interaction mediated by the W boson, we could test the various aspects of the standard model.
Precise measurements of the NC interaction were performed in a wide QィイD12ィエD1 range from 0.5GeVィイD12ィエD1 to 5000GeVィイD12ィエD1 in order to determine the proton structure functions. The results were well fitted with models based with the quantum chromodynamics. Charged ciurrent cross sections were measured with data taken in the previous years. The results were consistent with the prediction of the standard models The mass of W boson was extracted from the data to be consistent with that obtained by direct measurements. The analysis for the NC using full data showed an excess from the standard model prediction in the very high QィイD12ィエD1 region. Is is not yet excluded that this is due to a statistical fluctuation but it might be an effect of new particles such as leptoquarks. re-analysis on the CC cross sections was quickly performed by using the full data. Preliminary results were shown in a conference in June 1996. There was a tendency that the data were above the standard model prediction, although it is not yet conclusive due to lack of statistics and more ambiguity in the model prediction compared with the NC cross section.
We need more data in order to confirm the effect. HERA machine upgrade foreseen in year 2000 will give us this opportunity.