Search for invisible decays of Higgs bosons in the vector boson fusion and associated ZH production modes

TL;DR

This CMS study searches for invisible decays of Higgs bosons produced via vector boson fusion and ZH, using 7–8 TeV LHC data. It employs data-driven control regions and shape-based fits to set upper limits on the production cross section times invisible branching fraction, with a combined 125 GeV Higgs limit of B(H→inv) < 0.58 at 95% CL under SM production. The analysis translates these limits into Higgs-portal dark matter constraints, providing competitive bounds on DM–nucleon cross sections for light DM. The results improve upon indirect constraints and LEP limits, offering important insights into non-SM Higgs decays and their DM connections.

Abstract

A search for invisible decays of Higgs bosons is performed using the vector boson fusion and associated ZH production modes. In the ZH mode, the Z boson is required to decay to a pair of charged leptons or a b b-bar quark pair. The searches use the 8 TeV pp collision dataset collected by the CMS detector at the LHC, corresponding to an integrated luminosity of up to 19.7 inverse femtobarns. Certain channels include data from 7 TeV collisions corresponding to an integrated luminosity of 4.9 inverse femtobarns. The searches are sensitive to non-standard-model invisible decays of the recently observed Higgs boson, as well as additional Higgs bosons with similar production modes and large invisible branching fractions. In all channels, the observed data are consistent with the expected standard model backgrounds. Limits are set on the production cross section times invisible branching fraction, as a function of the Higgs boson mass, for the vector boson fusion and ZH production modes. By combining all channels, and assuming standard model Higgs boson cross sections and acceptances, the observed (expected) upper limit on the invisible branching fraction at m[H] = 125 GeV is found to be 0.58 (0.44) at 95% confidence level. We interpret this limit in terms of a Higgs-portal model of dark matter interactions.

Figures (13)

• Figure 1: The Feynman diagrams for Higgs production in the VBF (left), ${Z}(\ell\ell){H}\xspace$ (center) and ${Z}({b}\overline{{b}}\xspace){H}\xspace$ (right) channels. The Higgs boson is assumed to decay invisibly.
• Figure 2: Distributions of $M_\mathrm{jj}$ (top left), $\Delta \eta_\mathrm{jj}$ (top right), $\Delta \phi_\mathrm{jj}$ (bottom left), and central jet $p_{\mathrm{T}}$ (bottom right) in background and signal MC simulation. The distributions are shown after requiring two jets with $p_{\mathrm{T}}\xspace^\mathrm{j1},p_{\mathrm{T}}\xspace^\mathrm{j2} > 50$$\,\text{Ge\spaceV}$, $\lvert \eta \rvert < 4.7$, $\eta_\mathrm{j1}, \eta_\mathrm{j2} < 0$, $M_\mathrm{jj}>150$$\,\text{Ge\spaceV}$, and $E_{\mathrm{T}}^{\text{miss}}\xspace > 130$$\,\text{Ge\spaceV}$. The arrows correspond to the thresholds applied for the final selection, after optimization.
• Figure 3: The $E_{\mathrm{T}}^{\text{miss}}\xspace$ (top) and $M_\mathrm{jj}$ (bottom) distributions in the relaxed ${Z}$ control region of the VBF search, with no requirements on $\Delta \eta_\mathrm{jj}$, $\Delta \phi_\mathrm{jj}$, or CJV, and with the $M_\mathrm{jj}$ requirement relaxed to 1000$\,\text{Ge\spaceV}$. The simulated background from different processes is shown cumulatively, and normalized to the data, with its systematic uncertainty shown as a hatched region. The lower panels show the ratio of data to the simulated background, again with the systematic uncertainty shown as a hatched region.
• Figure 4: The $E_{\mathrm{T}}^{\text{miss}}\xspace$ (top) and $M_\mathrm{jj}$ (bottom) distributions in data and MC after the full selection in the VBF search signal region. The simulated background from different processes is normalized to the estimates obtained from control samples in data, and shown cumulatively, with the total systematic uncertainty shown as a hatched region. Note that the QCD multijet background is not shown due to limited MC statistics, which results in a small apparent discrepancy between data and the backgrounds shown at low values of $E_{\mathrm{T}}^{\text{miss}}\xspace$ and $M_\mathrm{jj}$. The cumulative effect of a signal from a Higgs boson with SM VBF production cross section, $m_{{H}\xspace}=125$$\,\text{Ge\spaceV}$ and $\mathcal{B}({H}\xspace\to\text{inv})$=100% is also shown.
• Figure 5: The distributions of $E_{\mathrm{T}}^{\text{miss}}\xspace$ (left), $\Delta \phi({\ell\ell,E_{\mathrm{T}}^{\text{miss}}\xspace})$ (center) , and $|E_{\mathrm{T}}^{\text{miss}}\xspace-p_{\mathrm{T}}\xspace^{\ell\ell}|/p_{\mathrm{T}}\xspace^{\ell\ell}$ (right) in data compared to the estimated background from simulation ($\mathrm{W}$${Z}$ and ${Z}{Z}$) or data (all other channels), before the optimization of the selection. The expected distributions from different background processes are displayed cumulatively, while a signal corresponding to $m_{{H}\xspace}=125$$\,\text{Ge\spaceV}$ and $\mathcal{B}({H}\xspace\to\text{inv})$=100% is superimposed separately. The arrows correspond to the cuts applied for the final selection as described at the end of Section \ref{['sec:zllh-sel']}. The statistical uncertainty in the background estimate is shown as a hatched region. The plots show the electron and muon channels combined. The lower panels show the ratio of data to the simulated background, again with the statistical uncertainty in the background shown as a hatched region.