A Revisit to Top Quark Forward-Backward Asymmetry

Abstract

We analyze various models for the top quark forward-backward asymmetry ($A_{FB}^t$) at the Tevatron, using the latest CDF measurements on different $A_{FB}^t$s and the total cross section. The axigluon model in Ref. \cite{paul} has difficulties in explaining the large rapidity dependent asymmetry and mass dependent asymmetry simultaneously and the parameter space relevant to $A_{FB}^t$ is ruled out by the latest dijet search at ATLAS. In contrast to Ref. \cite{cp}, 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 $Z^{\prime }$ \cite{hitoshi}, $W^{\prime }$\cite{waiyee} and diquark \cite{tim} models all have parameter regions that satisfy different $A_{FB}$ measurements within 1 $\sigma$. However, the heavy $Z^{\prime }$ model which can be marginally consistent with the total cross section is severely constrained by the Tevatron direct search of same-sign top quark pair. The diquark model suffers from too large total cross section and is difficult to fit the $t\bar{t}$ invariant mass distribution. The electroweak precision constraints on the $W^{\prime }$ model based on $Z^{\prime }$-$Z$ mixings is estimated and the result is rather weak ($m_{Z^{\prime }}>450$ GeV). Therefore, the heavy $W^{\prime }$ model seems to give the best fit for all the measurements. The $W^{\prime }$ model predicts the $t\bar{t}+j$ signal from $t{W}^{\prime }$ production and is 10%-50% of SM $t\bar{t}$ at the 7 TeV LHC. Such $t+j$ resonance can serve as the direct test of the $W^{\prime }$ model.

25 pages, 7 figures, 1 table

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Cited by in corpus (23)

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