Anomalous Top Couplings at Hadron Colliders Revisited

TL;DR

This paper revisits anomalous top couplings at hadron colliders using an effective operator approach, emphasizing the importance of including four-fermion contact terms and off-shell effects in analyzing single top production and bounds.

Contribution

It clarifies the complete set of operators affecting top couplings and demonstrates their impact on experimental bounds by incorporating full matrix elements and off-shell effects.

Findings

Four-fermion contact terms significantly affect top coupling bounds.

Full matrix element calculations alter the interpretation of experimental results.

Off-shell and interference effects are crucial for accurate top coupling analysis.

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 SM gauge bosons such as ttA, ttZ, tbW and ttg, the operator set can be restricted accordingly. However, the complete basis cannot be mapped onto an on-shell parametrisation 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.