Search for associated production of a $Z$ boson with an invisibly decaying Higgs boson or dark matter candidates at $\sqrt{s}=13$ TeV with the ATLAS detector

TL;DR

This paper reports a search for invisible Higgs decays and dark matter candidates produced with a Z boson in proton-proton collisions at 13 TeV, setting limits on branching ratios and model parameters using ATLAS data.

Contribution

It presents the first ATLAS search for invisible Higgs decays and dark matter in Z-associated production at 13 TeV with comprehensive limits.

Findings

Upper limit on Higgs invisible decay branching ratio is 19% at 95% CL.

Exclusion limits set for simplified dark matter and two-Higgs-doublet models.

Analysis uses 139 fb$^{-1}$ of LHC data.

Abstract

A search for invisible decays of the Higgs boson as well as searches for dark matter candidates, produced together with a leptonically decaying $Z$ boson, are presented. The analysis is performed using proton-proton collisions at a centre-of-mass energy of 13 TeV, delivered by the LHC, corresponding to an integrated luminosity of 139 fb$^{-1}$ and recorded by the ATLAS experiment. Assuming Standard Model cross-sections for $ZH$ production, the observed (expected) upper limit on the branching ratio of the Higgs boson to invisible particles is found to be 19% (19%) at the 95% confidence level. Exclusion limits are also set for simplified dark matter models and two-Higgs-doublet models with an additional pseudoscalar mediator.