Study of Elementary Particles Using OPAL Detector at LEP-II

欧洲核子研究中心世界上能量最高的e^+e^-对撞机LEP于1989年开始运行。在1995年完成了非常成功的Z共振物理项目后，LEP开始了能量升级项目LEP2。1996年，超过了足以产生成对W玻色子的碰撞能量。1997年LEP碰撞能量增加到183gev， 1998年进一步提高到189gev。我们主导的OPAL实验已经成功地在这个新能量区域采集了数据。为了充分利用这些数据，我们在了解探测器在高能下的性能，精确校准探测器，改进物理分析技术以获得测量精度和搜索灵敏度方面进行了研究，并进行了一些新的物理课题的研究。已收集到约4000 W对事件。精确测量了产生截面、总W宽和衰变分支比。W质量的精确测量，加上Z玻色子的精确结果，为标准模型的关键测试提供了信息。随着W对事件数据样本的增加，W质量测定的精度大大提高。对费米子对产生、Z对产生、单W产生和一般四费米子终态等多种标准模型过程进行了系统的研究。我们发现标准模型在这个高能量区域工作得很好。希格斯玻色子是标准模型的关键元素，但尚未被发现，它的质量比91 gev还要重。对超对称粒子进行了搜索，得到了理论参数的改进极限。

The world highest energy e^+e^- collider LEP at CERN has started its operation in 1989. After completion in 1995 of highly successful physics program at the Z resonance, LEP has started the energy upgrade program LEP2 in. 1996, exceeding the collision energy sufficient to produce the W boson in pair. In 1997 the LEP collision energy was increased to 183 GeV and further pushed up to 189 0eV in 1998. The OPAL experiment, in which we have been playing a leading role, has successfully collected data at this new energy region. In order to make full use of these data, we worked on understanding the detector performance at high energy, precise calibration of the detector, developments for improved physics analysis technique to gain precision of measurements and sensitivity for searches, and we also pursued a number of new physics topics.1. About 4000 W pairs events have been collected. The production cross-section, total W width and decay branching ratios were precisely measured. Accurate measurement of the W mass, together with the precision results of the Z boson, provides information for crucial tests of the Standard Model. Based on the increased data sample of W pair events, precision of W mass determination has been largely improved.2. Systematic investigations were made for varieties of Standard Model processes such as fermion pair production, Z pair production, single W production and general four-fermion final states. The Standard Model is found to work well at this higher energy region.3. The mass of the Higgs boson, which is a key element of the Standard Model yet undetected, is found to be heavier than about 91 GeV.4. Searches for Supersymmetric particles were performed and improved limits on the parameters in the theory have been obtained.