Anomalous t-c-g coupling: The Connection between Single Top Production and Top Decay

Continuing earlier work, we examine the constraint on an anomalous t-c-g coupling from top quark decay. We find that from current CDF measurements of the branching ratio t → Wb, the minimum scale at which new physics can strongly modify the t-c-g coupling is Λtcg ≥ about 950 GeV. At the upgraded Tevatron, single top production can constrain Λtcg ≥ 4.5 TeV. The connection between t-c production and the decay t → cg is examined, showing how constraints on one lead to a constraint on the other. As shown in [1], an anomalous coupling between top quark, charm quark, and gluon fields can have a large effect on single top production at the Tevatron. In that work, it was mentioned that the t-c-g operator can also be studied from the decay t → cg. This decay mode has been studied in [2], and the results are similar to those presented here. In [1] the ratio of the partial widths is presented, Rtcg = Γ(t → cg) Γ(t → Wb) = √ 2 64αsπm 2 t 3ΛGF [ 1− m 2 W m t ]2 [ 1 + 2 m W m t ] . (1) 1 The notation and conventions used in this work are the same as those presented in [1]. A full discussion of the effective operator which generates the t-c-g coupling can be found there-in. 1 Assuming that there is no other new physics modifying the top quark decays, the branching ratio BR(t → Wb) can be expressed as, BR(t → Wb) = Γ(t → Wb) Γ(t → Wb) + Γ(t → cg) . (2) From these results, one may determine the Λtcg which corresponds to a given lower limit on BR(t → Wb), bmin. The results are plotted in Figure-1.