CMS Discovery: toponium vs. CP-odd Higgs

Discussion from the experimental and theory side of this CMS discovery:
https://indico.ijclab.in2p3.fr/event/10259/contributions/35240/attachmen...

Experimental talk:

Twists in Top: Searching for Scalars, Pseudoscalars and Quasi-Bound States
in ttbar

In this seminar, a search for heavy pseudoscalar or scalar bosons decaying
to a top quark pair (tt̄) in final states with one or two charged leptons
will be presented. The results are based on 138 fb⁻¹ of proton-proton
collisions recorded by the CMS experiment between 2016 and 2018 at √s = 13
TeV. The invariant mass of the reconstructed tt̄ system, along with variables
sensitive to its spin state, is used to discriminate against the standard
model tt̄ background. An excess is observed in the data above the background
prediction, modeled using perturbative quantum chromodynamics (QCD) alone,
with a significance exceeding five standard deviations.

Three possible hypotheses to interpret the excess, which is located near the
tt̄ production threshold, will be discussed: (1) the production of a scalar
Higgs boson, (2) the production of a pseudoscalar Higgs boson, or (3) the
existence of a tt̄ quasi-bound state, as predicted in a simplified model of
nonrelativistic QCD. For the first two hypotheses, upper limits on the
coupling of scalar or pseudoscalar bosons to top quarks will be presented,
covering a mass range of 365–1000 GeV and relative widths of 0.5–25%. For
the third scenario, initial cross-section estimates will be shown, and the
stability of the result against alternative background predictions will be
discussed.

Theory talk:

To be or not to be toponium

The presence of toponium is expected to be visible as a wide
enhancement at the lower end of the top quark-antiquark kinematical
distribution. I will discuss how one could be reasonably sure that such
signal, if found, is due to toponium and not yet another mismodeling.