CMS Results at the $\text{t}\bar{\text{t}}$ threshold
Jörn Bach
TL;DR
The paper analyzes top-antitop production near threshold in CMS data at $\sqrt{s}=13$ TeV with $138~\mathrm{fb}^{-1}$, targeting heavy Higgs bosons and a possible $t\bar t$ bound state. By combining spin-correlation observables $c_{hel}$ and $c_{han}$ with the invariant mass $m_{tt}$, the study tests $A/H$ production via gluon fusion and NRQCD-inspired $\eta_t$ bound-state effects, using a 3D template approach. An excess near threshold favors a pseudoscalar $\eta_t$ with cross section $\sigma_{\eta_t}\approx 7.8$–8.8 pb, in agreement with NRQCD predictions, while scalar interpretations are disfavored; limits are set on $A$ and $H$ under a 5% width hypothesis and on their couplings. The results highlight threshold dynamics and motivate more refined bound-state modeling to distinguish bound-state effects from heavy-Higgs contributions.
Abstract
Recent results of CMS at the top-antitop quark pair production threshold in the dileptonic and semileptonic decay channels are presented. The results were obtained analyzing $138~\mathrm{fb}^{-1}$ of $pp$ collision data taken at $\sqrt{s}=13~\mathrm{TeV}$ with the CMS detector. Spin-sensitive variables are combined with the $t\bar t$ invariant mass $m_{t\bar t}$ to achieve high sensitivity for intermediate heavy pseudoscalar or scalar states. An excess in the data is observed for low values of $m_{t\bar t}$, favoring a pseudoscalar over a scalar hypothesis. The results are given in the interpretation of a simplified $t\bar t$ bound state model $η_t$ and in a generic model for heavy (pseudo)scalar production. The observed excess is compatible with non-relativistic QCD (NRQCD) calculations for a $t\bar t$ bound state.