ATLAS sensitivity to Wtb anomalous couplings in top quark decays

TL;DR

This paper evaluates the ATLAS experiment's ability to detect deviations in Wtb couplings in top quark decays, proposing new observables that enhance sensitivity and reduce systematic uncertainties, leading to more precise measurements.

Contribution

The study introduces new angular asymmetries and ratios of helicity fractions that improve sensitivity to anomalous Wtb couplings and reduce systematic uncertainties compared to traditional methods.

Findings

New observables have smaller systematic uncertainties.

Measurement sensitivity can reach a few percent.

Combining measurements enhances limits on anomalous couplings.

Abstract

We study the sensitivity of the ATLAS experiment to Wtb anomalous couplings in top pair production with semileptonic decay, pp -> t tbar -> W+ b W- bbar, with one of the W bosons decaying leptonically and the other hadronically. Several observables are examined, including the W helicity fractions and new quantities recently introduced, such as the ratios of helicity fractions and some angular asymmetries defined in the W rest frame. The dependence on anomalous couplings of all these observables has been previously obtained. In this work we show that some of the new observables also have smaller systematic uncertainties than the helicity fractions, with a dependence on anomalous couplings similar or stronger than for helicity fractions. Consequently, their measurement can significantly improve the limits on anomalous couplings. Moreover, the most sensitive measurements can be combined. In this case, the precision achieved in the determination of Wtb anomalous couplings can be of a few percent in the semileptonic channel alone.