Precision constraints on the top-quark effective field theory at future lepton colliders

TL;DR

This paper assesses how future lepton colliders can precisely constrain top-quark interactions beyond the standard model using optimal observables and effective field theory, providing basis-independent limits and analyzing the impact of different run parameters.

Contribution

It introduces a method using statistically optimal observables to efficiently constrain all relevant EFT operators simultaneously at future lepton colliders.

Findings

Optimal observables provide strong, basis-independent constraints.

Quadratic EFT contributions have negligible impact on limits.

The global determinant parameter identifies the most restrictive run configurations.

Abstract

We examine the constraints that future lepton colliders would impose on the effective field theory describing modifications of top-quark interactions beyond the standard model, through measurements of the $e^+e^-\to bW^+\:\bar bW^-$ process. Statistically optimal observables are exploited to constrain simultaneously and efficiently all relevant operators. Their constraining power is sufficient for quadratic effective-field-theory contributions to have negligible impact on limits which are therefore basis independent. This is contrasted with the measurements of cross sections and forward-backward asymmetries. An overall measure of constraints strength, the global determinant parameter, is used to determine which run parameters impose the strongest restriction on the multidimensional effective-field-theory parameter space.