Measuring the Invisible Higgs Width at the 7 and 8 TeV LHC

TL;DR

This paper evaluates the 7 and 8 TeV LHC's ability to detect an invisible Higgs decay, focusing on weak boson fusion channels, and finds the 7 TeV run particularly promising for probing branching fractions around 40%.

Contribution

It provides the first detailed estimates of the LHC's sensitivity to invisible Higgs decays at 7 and 8 TeV, highlighting the weak boson fusion channel as the most effective search method.

Findings

Weak boson fusion channel is most sensitive for invisible Higgs decays.

The 7 TeV LHC can probe branching fractions down to 40% with 20 fb^{-1}.

The 8 TeV LHC has comparable but not superior sensitivity to 7 TeV.

Abstract

The LHC is well on track toward the discovery or exclusion of a light Standard Model (SM)-like Higgs boson. Such a Higgs has a very small SM width and can easily have large branching fractions to physics beyond the SM, making Higgs decays an excellent opportunity to observe new physics. Decays into collider-invisible particles are particularly interesting as they are theoretically well motivated and relatively clean experimentally. In this work we estimate the potential of the 7 and 8 TeV LHC to observe an invisible Higgs branching fraction. We analyze three channels that can be used to directly study the invisible Higgs branching ratio at the 7 TeV LHC: an invisible Higgs produced in association with (i) a hard jet; (ii) a leptonic Z; and (iii) forward tagging jets. We find that the last channel, where the Higgs is produced via weak boson fusion, is the most sensitive, allowing branching fractions as small as 40% to be probed at 20 inverse fb for masses in the range between 120 and 170 GeV, including in particular the interesting region around 125 GeV. We provide an estimate of the 8 TeV LHC sensitivity to an invisibly-decaying Higgs produced via weak boson fusion and find that the reach is comparable to but not better than the reach at the 7 TeV LHC. We further estimate the discovery potential at the 8 TeV LHC for cases where the Higgs has substantial branching fractions to both visible and invisible final states.