Single top quark production at LHC with anomalous Wtb couplings

TL;DR

This paper analyzes how anomalous Wtb couplings affect single top production at the LHC, providing formulas for cross sections and estimating how measurements can constrain these couplings and V_tb.

Contribution

It derives simplified expressions for single top production cross sections with anomalous couplings assuming gauge invariance, and assesses their impact on experimental limits at the LHC.

Findings

Single top cross sections depend on specific anomalous couplings.

Measurement of single top production constrains V_tb and anomalous couplings.

Combining production and decay data improves limits on Wtb interactions.

Abstract

We investigate single top production in the presence of anomalous Wtb couplings. We explicitly show that, if these couplings arise from gauge invariant effective operators, the only relevant couplings for single top production and decay are the usual gamma^mu and sigma^mu nu q_nu terms, where q is the W boson momentum. This happens even in the single top production processes where the Wtb interaction involves off-shell top and/or bottom quarks. With this parameterisation for the Wtb vertex, we obtain expressions for the dependence on anomalous couplings of the single top cross sections, for (i) the t-channel process, performing a matching between tj and t bbar j production, where j is a light jet; (ii) s-channel t bbar production; (iii) associated tW- production, including the correction from tW- bbar. We use these expressions to estimate, with a fast detector simulation, the simultaneous limits which the measurement of single top cross sections at LHC will set on V_tb and possible anomalous couplings. Finally, a combination with top decay asymmetries and angular distributions is performed, showing how the limits can be improved when the latter are included in a global fit to Wtb couplings.