New physics in toponium's shadow?

TL;DR

This paper explores how a neutral pseudoscalar particle could influence top-antitop production near threshold, potentially explaining recent experimental enhancements and constraining new physics models.

Contribution

It introduces an effective framework combining Standard Model and new pseudoscalar physics to analyze threshold effects in top pair production.

Findings

Standard Model effects can partly explain the observed enhancements.

Pseudoscalar interactions can significantly alter the viable parameter space.

Current data are compatible with additional pseudoscalar contributions.

Abstract

ATLAS and CMS have recently reported enhancements in the top-antitop production rate near threshold, a region where non-perturbative QCD dynamics associated with toponium formation become relevant. We investigate how this behaviour is modified in the presence of a neutral pseudoscalar that couples to gluons and top quarks, using an effective description that consistently incorporates perturbative Standard Model and new physics contributions, their interference and non-perturbative threshold effects. We show that the combined effect of those ingredients markedly shapes the viable region of the pseudoscalar parameter space, particularly for narrow resonances with masses close to twice the top mass. While Standard Model threshold effects could explain a sizeable part of the measured enhancements, the current data remain compatible with additional contributions from pseudoscalar interactions.