Yerevan Physics Institute, Yerevan, Armenia.
Phys Rev Lett. 2013 Apr 26;110(17):172002. doi: 10.1103/PhysRevLett.110.172002. Epub 2013 Apr 25.
The first measurement of vector-boson production associated with a top quark-antiquark pair in proton-proton collisions at sqrt[s] = 7 TeV is presented. The results are based on a data set corresponding to an integrated luminosity of 5.0 fb(-1), recorded by the CMS detector at the LHC in 2011. The measurement is performed in two independent channels through a trilepton analysis of ttZ events and a same-sign dilepton analysis of ttV (V = W or Z) events. In the trilepton channel a direct measurement of the ttZ cross section σ(ttZ) = 0.28(-0.11)(+0.14) (stat)(-0.03)(+0.06) (syst) pb is obtained. In the dilepton channel a measurement of the ttV cross section yields σ(ttV) = 0.43(-0.15)(+0.17) (stat)(-0.07)(+0.09) (syst) pb. These measurements have a significance, respectively, of 3.3 and 3.0 standard deviations from the background hypotheses and are compatible, within uncertainties, with the corresponding next-to-leading order predictions of 0.137(-0.016)(+0.012) and 0.306(-0.053)(+0.031) pb.
首次在质子-质子对撞实验中测量到与顶夸克-反顶夸克对相关的矢量玻色子产生，对撞能量为 sqrt[s] = 7 TeV。该结果基于 2011 年 CMS 探测器在 LHC 上记录的 5.0 fb^(-1)积分亮度的数据。该测量通过 ttZ 事件的三轻子分析和 ttV（V = W 或 Z）事件的同号双轻子分析在两个独立的通道中完成。在三轻子通道中，直接测量 ttZ 截面 σ(ttZ) = 0.28(-0.11)(+0.14) (stat)(-0.03)(+0.06) (syst) pb。在双轻子通道中，ttV 截面的测量结果为 σ(ttV) = 0.43(-0.15)(+0.17) (stat)(-0.07)(+0.09) (syst) pb。这些测量结果相对于背景假设的显著性分别为 3.3 和 3.0 个标准差，并且在不确定性范围内与对应的次领头阶预测值 0.137(-0.016)(+0.012)和 0.306(-0.053)(+0.031) pb 是兼容的。
