Search for invisible Higgs-boson decays in events with vector-boson fusion signatures using 139 $\text{fb}^{-1}$ of proton-proton data recorded by the ATLAS experiment

TL;DR

This paper reports a search for invisible decays of Higgs bosons produced via vector-boson fusion using 139 fb^{-1} of proton-proton collision data from ATLAS, setting limits on decay rates and dark matter interactions.

Contribution

First direct search for invisible Higgs decays in VBF production at 13 TeV with the ATLAS detector, providing new upper limits and dark matter constraints.

Findings

No significant excess over Standard Model background.

Upper limit of 0.145 on Higgs invisible branching fraction at 95% CL.

Constraints on dark matter-nucleon scattering cross section.

Abstract

A direct search for Higgs bosons produced via vector-boson fusion and subsequently decaying into invisible particles is reported. The analysis uses 139 $\text{fb}^{-1}$ of $pp$ collision data at a centre-of-mass energy of $\sqrt{s}$=13 $\text{TeV}$ recorded by the ATLAS detector at the LHC. The observed numbers of events are found to be in agreement with the background expectation from Standard Model processes. For a scalar Higgs boson with a mass of 125 $\text{GeV}$ and a Standard Model production cross section, an observed upper limit of $0.145$ is placed on the branching fraction of its decay into invisible particles at 95% confidence level, with an expected limit of $0.103$. These results are interpreted in the context of models where the Higgs boson acts as a portal to dark matter, and limits are set on the scattering cross section of weakly interacting massive particles and nucleons. Invisible decays of additional scalar bosons with masses from 50 $\text{GeV}$ to 2 $\text{TeV}$ are also studied, and the derived upper limits on the cross section times branching fraction decrease with increasing mass from 1.0 $\text{pb}$ for a scalar boson mass of 50 $\text{GeV}$ to 0.1 $\text{pb}$ at a mass of 2 $\text{TeV}$.