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Top quark physics at colliders

对撞机中的顶级夸克物理

基本信息

批准号：
12640248
负责人：
HIKASA Ken-ichi
金额：
$ 1.73万
依托单位：
Tohoku University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2000
资助国家：
日本
起止时间：
2000 至 2001
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-12640248/
关键词：
elementary particle top quark collider super symmetry high energy physics ヒッグス粒子 QCD くりこみ中性カレント

项目摘要

1. Precise determination of the top quark mass may be made by measuring the cross section of the process e^+e^- → tt^^- near threshold. We find that theoretical error in the determination can be made small by using the <MS>^^^- mass instead of the pole mass as the parameter representing the top quark mass.2. We examine the bottomonium spectrum using higher order perturbative QCD calculation and find that the theory reproduces the data quite well, in contrary to the belief that perturbation theory is not applicable.3. We study the decay of the top squark in the mass region where the direct decay to the top quark is not kinematically allowed. We calculated the decay to a charm squark a neutralino via flavor-changing neutral current in the supergravity model by solving renormalization group equations. We show that this mode can be dominant when the parameter tan β is large. We further examine the case this mode competes with the charged current decay to a bottom squark and a chargino and propose a method to detect the top squark pair production events at hadron colliders4. Definition of the mixing matrix is nontrivial at higher orders in perturbation theory. We examine the gauge dependence of the mixing matrix and explicitly calculated the correction in several examples.5. It is known that the QCD correction for the decay of a Higgs boson to quarks and squarks is rather large. We find that a clever choice of the lowest-order parameter can reduce the size of the correction, leading to more reliable theoretical predictions.

1.通过测量阈值附近过程e^+e^- → tt^^-的横截面，可以精确确定顶夸克质量。我们发现，用<MS>^^^-质量代替极质量作为顶夸克质量的参数，可以减小测量中的理论误差.我们用高阶微扰QCD计算研究了bottomonium能谱，发现理论能很好地再现数据，与微扰理论不适用的观点相反.我们研究了在运动学上不允许直接衰变为顶夸克的质量区域中顶夸克的衰变。通过求解重整化群方程，计算了超引力模型中中性伴子通过变味中性流衰变为粲夸克的过程。我们发现，当参数tan β很大时，这种模式可以占主导地位。我们进一步研究的情况下，这种模式的竞争与带电电流衰减到底部的夸克和chargino，并提出了一种方法来检测在强子对撞机4的顶部夸克对生产事件。在微扰论中，混合矩阵的定义在高阶是非平凡的。我们研究了混合矩阵的规范依赖性，并在几个例子中明确计算了校正。已知希格斯玻色子衰变为夸克和方夸克的QCD修正是相当大的。我们发现，最低阶参数的巧妙选择可以减小校正的大小，从而得到更可靠的理论预测。