Search for a heavy Higgs boson decaying into a $Z$ boson and another heavy Higgs boson in the $\ell\ell bb$ final state in $pp$ collisions at $\sqrt{s}=13$ TeV with the ATLAS detector

TL;DR

This paper searches for a heavy Higgs boson decaying into a Z boson and another heavy Higgs, using 13 TeV proton-proton collision data, setting upper limits on production cross-sections without finding evidence of such particles.

Contribution

First search for the decay of a heavy neutral Higgs into a Z and another Higgs in the $ ext{ell} ext{ell}bb$ final state at 13 TeV with ATLAS, providing new upper limits.

Findings

No evidence for heavy Higgs boson production was observed.

Set 95% CL upper limits on cross-section times branching ratio.

Results constrain two-Higgs-doublet model parameters.

Abstract

A search for a heavy neutral Higgs boson, $A$, decaying into a $Z$ boson and another heavy Higgs boson, $H$, is performed using a data sample corresponding to an integrated luminosity of 36.1 fb$^{-1}$ from proton-proton collisions at $\sqrt{s} = 13$ TeV recorded in 2015 and 2016 by the ATLAS detector at the Large Hadron Collider. The search considers the $Z$ boson decaying to electrons or muons and the $H$ boson into a pair of $b$-quarks. No evidence for the production of an $A$ boson is found. Considering each production process separately, the 95% confidence-level upper limits on the $pp\rightarrow A\rightarrow ZH$ production cross-section times the branching ratio $H\rightarrow bb$ are in the range of 14-830 fb for the gluon-gluon fusion process and 26-570 fb for the $b$-associated process for the mass ranges 130-700 GeV of the $H$ boson and process for the mass ranges 130-700 GeV of the $H$ boson and 230-800 GeV of the $A$ boson. The results are interpreted in the context of the two-Higgs-doublet model.