Heavy Higgs decay to $t\bar{t} Z$ and constraints on a $750$ GeV pseudoscalar

TL;DR

This paper investigates heavy Higgs boson decays involving top quarks and Z bosons, constrains a 750 GeV pseudoscalar using existing measurements, and discusses implications for the diphoton excess and related decay channels.

Contribution

It recasts existing $t\bar{t}Z$ measurements to set limits on heavy Higgs decay processes and constrains a 750 GeV pseudoscalar model with multiple decay channels.

Findings

Limits on heavy Higgs decay rates up to 750 GeV mass.

Constraints on the 750 GeV pseudoscalar's decay widths.

The heavy Higgs mass is suggested to be near 650 GeV.

Abstract

In models with multiple nondegenerate Higgs bosons, the decay chain $H/A \to A/H Z\to t\bar{t} Z$ may have a partial width comparable to the $t\bar{t}$ decay mode. We recast the ATLAS standard model $t\bar{t} Z$ measurement to put limits on the rate for this process. Limits are also set on the two Higgs doublet model at low $\tan \beta$ that are sensitive to a heavy Higgs mass as high as $\sim 750$ GeV. We then discuss the $750$ GeV diphoton excess in terms of a pseudoscalar that also has the decays $A\to HZ$ and $A\to H^\pm W^\mp$. These decays strongly constrain the partial widths for $A\to\gamma\gamma$ and $A\to gg$ when combined with the $t\bar t$ resonance search limits. In a benchmark model the mass of $H$ should be close to 650 GeV.