Christian Schwanenberger (DESY), "Does the Top Quark Embrace Its Antipode? Unveiling a Pseudoscalar Excess near the $t\bar{t}$ Threshold"

Thursday 26 Mar 2026, 15:00 → 17:00 US/Eastern

The top quark — the heaviest known elementary particle — plays a unique role at the energy frontier of the Large Hadron Collider (LHC). Using CMS data collected between 2016 and 2018 at a center-of-mass energy of √s = 13 TeV, we searched for resonances in top–antitop quark pair ($t\bar{t}$) production. The analysis probes the invariant mass of the $t\bar{t}$ system and angular observables that reveal subtle effects of the correlation between the top and antitop quark spins. A significant excess of events appears near the kinematic $t\bar{t}$ threshold, deviating from predictions of fixed-order perturbative QCD. The observed enhancement is consistent with the production of a color-singlet pseudoscalar quasi-bound “toponium’’ state — long thought unobservable — as predicted by non-relativistic QCD. 

 

I will present these results, compare them with recent ATLAS findings confirming the excess, and discuss alternative interpretations such as resonances through production of new elementary scalars or pseudoscalars.

 

 

Julia Münstermann (“Toponium, 2025, Cyanotype”)

Artistic representation of a connection between a top quark and its antiparticle.