Anomalous top couplings at hadron colliders revisited

Abstract

In an effective operator approach, the full set of leading contributions to anomalous top couplings comprises various new trilinear as well as higher interaction vertices, some of which are related to one another by gauge symmetry or equations of motion. In order to study trilinear top couplings to Standard Model gauge bosons such as $tt\ensuremath{\gamma}$, $ttZ$, $tbW$ and $ttg$, the operator set can be restricted accordingly. However, the complete basis cannot be mapped onto an on-shell parametrization of the trilinear vertices alone. Four-fermion contact terms $qqtt$ and $udtb$ must be included if the relation to the operator basis is to be retained. In this paper, we point out how these interactions contribute to the single top search channels for anomalous trilinear $tbW$ couplings at the LHC and Tevatron, thus affecting the corresponding bounds. All results are based on full leading-order partonic matrix elements, thus automatically accounting for off-shell and interference effects as well as irreducible backgrounds. A discussion of the quantitative effects of going from on-shell tops to full matrix elements including acceptance cuts is also provided.