Colloquium, Christian Schwanenberger (DESY), "Does the Top Quark Embrace Its Antipode? Unveiling a Pseudoscalar Excess near the $t\bar{t}$ Threshold"
by
Besprechungsraum 3A.1/2 (PSK)
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.
