Looking for an Invisible Higgs Signal at the LHC

TL;DR

This paper investigates the potential to detect an invisible Higgs decay at the LHC through vector boson fusion and associated Z production channels, analyzing sensitivities at 8 and 14 TeV for various luminosities.

Contribution

It provides a detailed analysis of the LHC's sensitivity to invisible Higgs decays in different production modes and decay channels, extending previous studies with updated methods and luminosity scenarios.

Findings

VBF channel can detect up to 80% invisible branching ratio at 5σ with 20-30 fb⁻¹.

Sensitivity improves to 25% invisible branching ratio at 14 TeV with 300 fb⁻¹.

Associated ZH production has more modest reach, with 3.5σ at 8 TeV and up to 8σ at 14 TeV for high luminosity.

Abstract

While the recent discovery of a Higgs-like boson at the LHC is an extremely important and encouraging step towards the discovery of the {\it complete} standard model(SM), the current information on this state does not rule out possibility of beyond standard model (BSM) physics. In fact the current data can still accommodate reasonable values of the branching fractions of the Higgs into a channel with `invisible' decay products, such a channel being also well motivated theoretically. In this study we revisit the possibility of detecting the Higgs in this invisible channel for both choices of the LHC energies, 8 and 14 TeV, for two production channels; vector boson fusion(VBF) and associated production($ZH$). In the latter case we consider decays of the $Z$ boson into a pair of leptons as well as a $b \bar b$ pair. For the VBF channel the sensitivity is found to be more than $5 \sigma$ at both the energies up to an invisible branching ratio ${\cal B}r_{invis} \sim 0.80$, with luminosities $\sim 20/30 {\rm fb}^{-1}$. The sensitivity is further extended to values of ${\cal B}r_{invis} \sim 0.25$ for $300 {\rm fb}^{-1}$ at 14 TeV. However the reach is found to be more modest for the $ZH$ mode with leptonic final state; with about $3.5 \sigma$ for the planned luminosity at 8 TeV, reaching $8 \sigma$ only for 14 TeV for $50 {\rm fb}^{-1}$. In spite of the much larger branching ratio of the $Z$ into a $b \bar b$ channel compared to the dilepton case, the former channel, can provide useful reach upto ${\cal B}r_{invis} \gsim 0.75$, only for the higher luminosity ($300{\rm fb}^{-1}$) option using jet-substructure and jet clustering methods for $b$-jet identification.