Bounds on Invisible Higgs Boson Decays Extracted from LHC $t\overline{t}H$ Production Data

We present an upper bound on the branching fraction of the Higgs boson to invisible particles by recasting a CMS Collaboration search for stop quarks decaying to $t\overline{t}+E_{\mathrm{T}}^{\text{miss}}$. The observed (expected) bound, $\mathrm{BF}(H\to \text{inv}.)<0.40(0.65)$ at 95% C.L., is the strongest direct limit to date, benefiting from a downward fluctuation in the CMS data in that channel. In addition, we combine this new constraint with existing published constraints to give an observed (expected) bound of $\mathrm{BF}(H\to \text{inv}.)<0.40(0.40)$ at 95% C.L., and we show some of the implications for theories of dark matter which communicate through the Higgs portal.

Figure 1

Diagrams for the production modes used in searches for invisible decay of the Higgs boson. The $VH$ mode (left panel), the vector-boson-fusion mode (center panel), and the $t\overline{t}H$ mode (right panel) are considered here.

Figure 2

Kinematics of $t\overline{t}H$ with $H\to \text{invisible}$ and all $t\overline{t}$ decay modes, compared to the two dominant backgrounds, SM top quark production with either single-lepton ($\ell \nu bq{q}^{\prime }b$) or dilepton ($\ell \nu b{\ell }^{\prime }\nu b$) decay modes. Distributions are shown of $M_T$, the transverse mass; $M_{T2}^W$, as defined in Ref. [19]; ${\chi }_{\mathrm{had}}^2$, the consistency of the $jjb$ system with a top quark hadronic decay; and $\min (\mathrm{\Delta }\varphi [\mathrm{MET},\text{jet}])$, the minimum angle between the $E_{\mathrm{T}}^{\text{miss}}$ and any jet. Distributions are shown after requiring exactly one lepton, at least four jets, and one $b$ tag.

Figure 3

(Top panel) Display of 95% C.L. upper limits on $\sigma (t\overline{t}H)\times \mathrm{BF}(H\to \text{inv}.)$, including both expected and observed limits. Also shown is the SM rate of $\sigma (t\overline{t}H)$ [26]. (Bottom panel) Ratio of the constraint to the SM $\sigma (t\overline{t}H)$ cross section.

Figure 4

Translation of the bound on $\mathrm{BF}(H\to \text{inv}.)<0.40$ into a constraint on the spin-independent scattering of Higgs portal dark matter with nucleons, for scalar DM (solid blue curves) and fermion DM (solid red curves). The envelope around each constraint represents the uncertainty in the hadronic matrix elements. Also shown are constraints from LUX [31] and XENON10 [32].