# Fitting the Strong Coupling Constant with Soft-Drop Thrust

## TL;DR

This paper investigates the use of soft-drop thrust in $e^+e^-$ collisions to improve the precision of the strong coupling constant $_s$ measurements by reducing hadronisation effects, using NLO+NLL theoretical predictions and pseudo data.

## Contribution

It demonstrates that soft-drop grooming reduces hadronisation corrections in $_s$ fits and enables extending the fitting range to lower thrust values while maintaining fit stability.

## Key findings

- Grooming reduces the shift in $_s$ due to hadronisation.
- Soft drop allows fitting at lower thrust values with stable results.
- The method shows promise for precise $_s$ determination at $e^+e^-$ colliders.

## Abstract

Soft drop has been shown to reduce hadronisation effects at $e^+e^-$ colliders for the thrust event shape. In this context, we perform fits of the strong coupling constant for the soft-drop thrust distribution at NLO+NLL accuracy to pseudo data generated by the \textsf{Sherpa}~event generator. In particular, we focus on the impact of hadronisation corrections, which we estimate both with an analytical model and a Monte-Carlo based one, on the fitted value of $\alpha_s(m_Z)$. We find that grooming can reduce the size of the shift in the fitted value of $\alpha_s$ due to hadronisation. In addition, we also explore the possibility of extending the fitting range down to significantly lower values of (one minus) thrust. Here, soft drop is shown to play a crucial role, allowing us to maintain good fit qualities and stable values of the fitted strong coupling. The results of these studies show that soft-drop thrust is a promising candidate for fitting $\alpha_s$ at $e^+ e^-$ colliders with reduced impact of hadronisation effects.