Thursday, November 27, 2025, 16:00
WBGB/019
Christian Schwanenberger, DESY Hamburg
Abstract:
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 (tt̄) production. The analysis
probes the invariant mass of the tt̄ 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 tt̄ 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.