CMS-PAS-HIG-22-013

CMS-PAS-HIG-22-013
Search for heavy pseudoscalar and scalar bosons decaying to top quark pairs in proton-proton collisions at $ \sqrt{s}= $ 13 TeV
CMS Collaboration
1 October 2024

Abstract: A search for heavy pseudoscalar or scalar bosons decaying to a top quark pair ($ \mathrm{t\bar{t}} $) in final states with one or two charged leptons is presented, using 138 fb$ ^{-1} $ of proton-proton collisions at $ \sqrt{s}= $ 13 TeV recorded by the CMS experiment at the CERN LHC. The invariant mass of the reconstructed $ \mathrm{t\bar{t}} $ system and variables sensitive to its spin state are used to discriminate against the standard model $ \mathrm{t\bar{t}} $ background. An excess of the data above the background prediction, as modeled using perturbative quantum chromodynamics (QCD) only, is observed. The excess is located close to the $ \mathrm{t\bar{t}} $ production threshold and it significantly favors the pseudoscalar signal hypothesis over the scalar hypothesis. It is compatible with the production of a $ ^1S_0^{[1]}$ $\mathrm{t\bar{t}} $ bound state ($ \eta_{\mathrm{t}} $), as predicted by a simplified model of nonrelativistic QCD, with a cross section of 7.1 pb and an uncertainty of 11%. The excess has a significance of above five standard deviations. Including the $ \eta_{\mathrm{t}} $ contribution in the background modeling, exclusion limits at 95% confidence level are set on the coupling of further pseudoscalar or scalar bosons to top quarks in a mass range of 365-1000 GeV and relative widths of 0.5-25%.
Links: CDS record (PDF) ; Physics Briefing ; CADI line (restricted) ; These preliminary results are superseded in this paper, Submitted to ROPP. The superseded preliminary plots can be found here.

CMS Publications