Search for anomalous $\boldmath{Wtb}$ couplings in single top quark production

TL;DR

This study analyzes 0.9 fb$^{-1}$ of $p ar p$ collision data to investigate the Lorentz structure of the $Wtb$ coupling in single top quark production, setting first direct limits on anomalous tensor couplings.

Contribution

It provides the first direct constraints on a general $Wtb$ interaction, including tensor couplings, using experimental data from single top quark production.

Findings

Data favor the standard model's left-handed vector coupling.

Upper limits are set on right-handed vector and tensor couplings.

First direct limits on general $Wtb$ interactions and tensor couplings.

Abstract

In 0.9 fb$^{-1}$ of $p \bar p$ collisions, D0 has observed an excess of events with an isolated lepton, missing transve rse momentum, and two to four jets. This excess is consistent with single top quark production. We examine these data to study the Lorentz structure of the $Wtb$ coupling. The standard model predicts a left-handed vector coupling at the $Wt b$ vertex. The most general lowest dimension, CP-conserving Lagrangian admits right-handed vector and left- or right-h anded tensor couplings as well. We find that the data prefer the left-handed vector coupling and set upper limits on the anomalous couplings. These are the first direct constraints on a general $Wtb$ interaction and the first direct limits on left- and right-handed tensor couplings.