分类： 物理学 >> 基本粒子与场物理学 提交时间： 2017-08-03
摘要： We analyze various models for the top quark forward-backward asymmetry ( A t F B) at the Tevatron, using the latest CDF measurements on different At F Bs and the total cross section. The axigluon model in Ref. [5] has difficulties in explaining the large rapidity dependent asymmetry and mass dependent asymmetry simultaneously and the parameter space relevant to A t F B is ruled out by the latest dijet search at ATLAS. In contrast to Ref. [8], we demonstrate that the large parameter space in this model with a U(1) d flavor symemtry is not ruled out by flavor physics. The t-channel flavor-violating Z ′ , W ′ and diquark models all have parameter regions that satisfy different AF B measurements within 1 σ. However, the heavy Z ′ model which can be marginally consistent with the total cross section is severely constrained by the Tevatron direct search of samesign top quark pair. The diquark model suffers from too large total cross section and is difficult to fit the t t¯ invariant mass distribution. The electroweak precision constraints on the W ′ model based on Z ′ - Z mixings is estimated and the result is rather weak ( m Z ′ > 450 GeV). Therefore, the heavy W ′ model seems to give the best fit for all the measurements. The W ′ model predicts the t t¯ + j signal from tW ′ production and is 10%-50% of SM t t¯ at the 7 TeV LHC. Such t + j resonance can serve as the direct test of the W ′ model.
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