Institut für Theoretische Teilchenphysik, Karlsruhe Institute of Technology, D-76128 Karlsruhe, Germany. otto.eberhardt@kit,edu
Phys Rev Lett. 2012 Dec 14;109(24):241802. doi: 10.1103/PhysRevLett.109.241802. Epub 2012 Dec 11.
We perform a comprehensive statistical analysis of the standard model (SM) with three and four generations using the latest Higgs search results from LHC and Tevatron, the electroweak precision observables measured at LEP and SLD, and the latest determinations of M(W), m(t), and α(s). For the three-generation case we analyze the tensions in the electroweak fit by removing individual observables from the fit and comparing their predicted values with the measured ones. In particular, we discuss the impact of the Higgs search results on the deviations of the electroweak precision observables from their best-fit values. Our indirect prediction of the top mass is m(t) =175.7(-2.2)(+3.0) GeV at 68.3% C.L., which is in good agreement with the direct measurement. We also plot the preferred area in the M(W)-m(t) plane. The best-fit Higgs boson mass is 126.0 GeV. For the case of the SM with a perturbative sequential fourth fermion generation (SM4) we discuss the deviations of the Higgs signal strengths from their best-fit values. The H → γγ signal strength now disagrees with its best-fit SM4 value at more than 4σ. We perform a likelihood-ratio test to compare the SM and SM4 and show that the SM4 is excluded at 5.3σ. Without the Tevatron data on H → bb the significance drops to 4.8σ.
我们使用来自 LHC 和 Tevatron 的最新 Higgs 搜索结果、LEP 和 SLD 测量的电弱精密观测值以及最新的 M(W)、m(t) 和 α(s) 测定值，对具有三代和四代的标准模型（SM）进行了全面的统计分析。对于三代模型，我们通过从拟合中移除单个观测值并比较它们的预测值与测量值来分析电弱拟合中的紧张局势。特别是，我们讨论了 Higgs 搜索结果对电弱精密观测值与其最佳拟合值的偏差的影响。我们对顶夸克质量的间接预测为 m(t) =175.7(-2.2)(+3.0) GeV，置信度为 68.3%，与直接测量结果非常吻合。我们还绘制了 M(W)-m(t) 平面上的首选区域。最佳拟合 Higgs 玻色子质量为 126.0 GeV。对于具有微扰序贯第四费米子代（SM4）的 SM 情况，我们讨论了 Higgs 信号强度与其最佳拟合值的偏差。H → γγ 信号强度现在与最佳拟合的 SM4 值不符，超过 4σ。我们进行了似然比检验来比较 SM 和 SM4，并表明 SM4 在 5.3σ 处被排除。如果没有 Tevatron 关于 H → bb 的数据，显著性下降到 4.8σ。
