Search for heavy pseudoscalar and scalar bosons decaying to a top quark pair in proton-proton collisions at $\sqrt{s}$ = 13 TeV

Abstract

A search for pseudoscalar or scalar bosons decaying to a top quark pair ($\mathrm{t}\bar{\mathrm{t}}$) in final states with one or two charged leptons is presented. The analyzed proton-proton collision data was recorded at $\sqrt{s}$ = 13 TeV by the CMS experiment at the CERN LHC and corresponds to an integrated luminosity of 138 fb${}^{-1}$. The invariant mass $m_{\mathrm{t}\bar{\mathrm{t}}}$ of the reconstructed $\mathrm{t}\bar{\mathrm{t}}$ system and variables sensitive to its spin and parity are used to discriminate against the standard model $\mathrm{t}\bar{\mathrm{t}}$ background. Interference between pseudoscalar or scalar boson production and the standard model $\mathrm{t}\bar{\mathrm{t}}$ continuum is included, leading to peak-dip structures in the $m_{\mathrm{t}\bar{\mathrm{t}}}$ distribution. An excess of the data above the background prediction, based on perturbative quantum chromodynamics (QCD) calculations, is observed near the kinematic $\mathrm{t}\bar{\mathrm{t}}$ production threshold, while good agreement is found for high $m_{\mathrm{t}\bar{\mathrm{t}}}$. The data are consistent with the background prediction if the contribution from the production of a color-singlet ${}^1{\mathrm{S}}_0^{[1]}$ $\mathrm{t}\bar{\mathrm{t}}$ quasi-bound state ${\eta }_{\mathrm{t}}$, predicted by nonrelativistic QCD, is added. Upper limits at 95% confidence level are set on the coupling between the pseudoscalar or scalar bosons and the top quark for boson masses in the range 365$-$1000 GeV, relative widths between 0.5 and 25%, and two background scenarios with or without ${\eta }_{\mathrm{t}}$ contribution.

Replaced with the published version. Added the journal reference and the DOI. All the figures and tables can be found at http://cms-results.web.cern.ch/cms-results/public-results/publications/HIG-22-013 (CMS Public Pages)

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