Yerevan Physics Institute, Yerevan, Armenia.
Phys Rev Lett. 2011 Dec 30;107(27):271802. doi: 10.1103/PhysRevLett.107.271802. Epub 2011 Dec 29.
A search for pair-produced heavy vectorlike charge-2/3 quarks, T, in pp collisions at a center-of-mass energy of 7 TeV, is performed with the CMS detector at the LHC. Events consistent with the flavor-changing-neutral-current decay of a T quark to a top quark and a Z boson are selected by requiring two leptons from the Z-boson decay, as well as an additional isolated charged lepton. In a data sample corresponding to an integrated luminosity of 1.14 fb(-1), the number of observed events is found to be consistent with the standard model background prediction. Assuming a branching fraction of 100% for the decay T→tZ, a T quark with a mass less than 475 GeV/c(2) is excluded at the 95% confidence level.
使用 LHC 上的 CMS 探测器，在质心能量为 7 TeV 的 pp 碰撞中搜索产生重矢量味荷为 2/3 的夸克 T 的事例。通过要求 Z 玻色子衰变中存在两个轻子以及一个额外的孤立带电轻子，选择符合味变中性电流衰变的 T 夸克衰变为 top 夸克和 Z 玻色子的事例。在对应于 1.14 fb(-1)积分亮度的一个数据样本中，观察到的事例数与标准模型背景预测相符。假设 T 夸克衰变为 tZ 的分支比为 100%，则在 95%置信水平下排除了质量小于 475 GeV/c(2)的 T 夸克。
