Search for heavy scalar or pseudoscalar states in $\mathrm{t \bar{t}}$ events at CMS

TL;DR

This paper reports a search for heavy scalar or pseudoscalar particles decaying into top quark pairs using CMS data, observing an excess at low invariant mass and setting limits on their couplings.

Contribution

It introduces a comprehensive analysis of $ ext{t}ar{ ext{t}}$ events at 13 TeV, exploring both scalar and pseudoscalar hypotheses with new limits on their couplings.

Findings

Observed excess at low $ ext{t}ar{ ext{t}}$} mass favoring pseudoscalar hypothesis.

Good agreement with models of (pseudo)scalar boson production and $ ext{t}ar{ ext{t}}$ bound states.

Set limits on couplings of (pseudo)scalar bosons to top quarks.

Abstract

A search for scalar or pseudoscalar states decaying to a top quark-antiquark pair ($\mathrm{t \bar{t}}$), using $138\,\mathrm{fb}^{-1}$ of pp collision data taken at $\sqrt{s} = 13\,\mathrm{TeV}$ using the CMS detector, is presented. Events with one or two leptons are analyzed using the invariant $\mathrm{t \bar{t}}$ mass ($m_{\mathrm{t \bar{t}}}$) as well as angular and spin correlation observables. An excess in the data is observed for low values of $m_{\mathrm{t \bar{t}}}$, preferring a pseudoscalar over a scalar hypothesis. It is interpreted in terms of a generic model of (pseudo)scalar boson production, as well as a simplified model of a $\mathrm{t \bar{t}}$ bound state ($\eta_{\mathrm{t}}$), yielding good agreement with the data. Moreover, limits on the couplings of additional (pseudo)scalar bosons to top quarks are set.