CMS-PAS-HIG-18-008

CMS-PAS-HIG-18-008
First constraints on invisible Higgs boson decays using $\mathrm{t}\bar{\mathrm{t}}\mathrm{H}$ production at $\sqrt{s}=$ 13 TeV
CMS Collaboration
March 2019

Abstract: This document presents first upper bounds on the branching fraction of the Higgs boson to invisible particles using an event topology corresponding to production of the Higgs boson in association with a top quark pair. This is done by reinterpreting results of the searches for scalar top quarks performed in the all-hadronic, the semi-leptonic, and the di-leptonic final states. Proton-proton collision data at $\sqrt{s}=$ 13 TeV is used, recorded with the CMS detector at the CERN Large Hadron Collider in 2016 and corresponding to an integrated luminosity of 35.9 fb $^{-1}$ . An observed (expected) upper limit of $\mathcal{B}(\mathrm{H}\to\mathrm{inv}) <$ 0.46 (0.48) is set on the branching fraction of the Higgs boson decaying to invisible particles at the 95% confidence level, assuming standard model $\mathrm{t}\bar{\mathrm{t}}\mathrm{H}$ production cross section.
Links: CDS record (PDF) ; inSPIRE record ; CADI line (restricted) ;

Figures & Tables	Summary	References	CMS Publications

Additional information on efficiencies needed for reinterpretation of these results are available here.
Additional technical material for CMS speakers can be found here

Figures
png pdf	Figure 1: Example leading-order diagram corresponding to pair production of top squarks ( ${\tilde{\mathrm {t}}} {\overline {\tilde{\mathrm {t}}}}$ ) predicted by SUSY (left). The process results in the production of two top quarks and ${{p_{\mathrm {T}}} ^\text {miss}}$ corresponding to undetected neutralinos. The same topology can be produced via a ${{{\mathrm {t}\overline {\mathrm {t}}}} {\mathrm {H}}}$ process with the Higgs boson decaying to invisible particles (right).
png pdf	Figure 1-a: Example leading-order diagram corresponding to pair production of top squarks ( ${\tilde{\mathrm {t}}} {\overline {\tilde{\mathrm {t}}}}$ ) predicted by SUSY. The process results in the production of two top quarks and ${{p_{\mathrm {T}}} ^\text {miss}}$ corresponding to undetected neutralinos.
png pdf	Figure 1-b: The topology that consists in two top quarks and ${{p_{\mathrm {T}}} ^\text {miss}}$ can also be produced via a ${{{\mathrm {t}\overline {\mathrm {t}}}} {\mathrm {H}}}$ process with the Higgs boson decaying to invisible particles.
png pdf	Figure 2: Observed data events, background predictions and signal expectations assuming 100% branching fraction are shown for the all hadronic search regions. Details of the selection applied is displayed on each plot. Ratios of the observed to SM predicted event counts are shown in the lower panel of each plot. The shaded blue band represents the statistical and systematic uncertainty in the prediction.
png pdf	Figure 2-a: Observed data events, background predictions and signal expectations assuming 100% branching fraction are shown for the all hadronic search regions. Details of the selection applied is displayed on the plot. Ratios of the observed to SM predicted event counts are shown in the lower panel. The shaded blue band represents the statistical and systematic uncertainty in the prediction.
png pdf	Figure 2-b: Observed data events, background predictions and signal expectations assuming 100% branching fraction are shown for the all hadronic search regions. Details of the selection applied is displayed on the plot. Ratios of the observed to SM predicted event counts are shown in the lower panel. The shaded blue band represents the statistical and systematic uncertainty in the prediction.
png pdf	Figure 2-c: Observed data events, background predictions and signal expectations assuming 100% branching fraction are shown for the all hadronic search regions. Details of the selection applied is displayed on the plot. Ratios of the observed to SM predicted event counts are shown in the lower panel. The shaded blue band represents the statistical and systematic uncertainty in the prediction.
png pdf	Figure 2-d: Observed data events, background predictions and signal expectations assuming 100% branching fraction are shown for the all hadronic search regions. Details of the selection applied is displayed on the plot. Ratios of the observed to SM predicted event counts are shown in the lower panel. The shaded blue band represents the statistical and systematic uncertainty in the prediction.
png pdf	Figure 3: Results of the background predictions, signal expectations, and data yields of the full 2016 data for the signal regions of the semi-leptonic analysis. The uncertainties, which are the quadratic sums of statistical and systematic uncertainties, are shown as shaded band. The ratio plot shows data over full prediction. A 100% branching fraction is assumed for the ${{\mathrm {t}\overline {\mathrm {t}}}}$ + ${\mathrm {H}} \to {{\mathrm {t}\overline {\mathrm {t}}}}$ + $\mathrm {inv.}$ signal.
png pdf	Figure 4: Predicted backgrounds and observed yields in the dilepton channel. The numbers on the x-axis indicate different signal regions. The hatched band shows the uncertainties discussed in the text. A 100% branching fraction is assumed for the ${{\mathrm {t}\overline {\mathrm {t}}}}$ + ${\mathrm {H}} \to {{\mathrm {t}\overline {\mathrm {t}}}}$ + $\mathrm {inv.}$ signal.
png pdf	Figure 5: Observed and expected 95% CL upper limits on $\sigma {{\mathcal {B}({{\mathrm {H}} \to \mathrm {inv}})}} /\sigma _{\textrm {SM}}$ for the all-hadronic, semi-leptonic, and di-leptonic final states, as well as their combination, assuming an SM Higgs boson with a mass of 125 GeV (left). The solid curves represent the observations in data, while the dashed lines represent the expected result assuming the absence of any signal. Profile likelihood ratios as a function of ${\mathcal {B}({{\mathrm {H}} \to \mathrm {inv}})}$ (right). The observed and expected likelihood scans are reported for the combination, as well as for the all-hadronic, semi-leptonic, and di-leptonic final states, repectively.
png pdf	Figure 5-a: Observed and expected 95% CL upper limits on $\sigma {{\mathcal {B}({{\mathrm {H}} \to \mathrm {inv}})}} /\sigma _{\textrm {SM}}$ for the all-hadronic, semi-leptonic, and di-leptonic final states, as well as their combination, assuming an SM Higgs boson with a mass of 125 GeV. The solid curves represent the observations in data, while the dashed lines represent the expected result assuming the absence of any signal.
png pdf	Figure 5-b: Profile likelihood ratios as a function of ${\mathcal {B}({{\mathrm {H}} \to \mathrm {inv}})}$ . The observed and expected likelihood scans are reported for the combination, as well as for the all-hadronic, semi-leptonic, and di-leptonic final states, repectively.

Tables
png pdf	Table 1: Summary of the signal systematic uncertainties with their typical ranges in individual signal bins for the three channels.

Summary

The first CMS limits on the branching fraction of invisible Higgs boson decays in the

${\mathrm{t\bar{t}}\mathrm{H}}$ production channel are presented. The results are obtained by recasting and combining the results of three searches for direct scalar top pair production using the data sample of proton-proton collisions collected with the CMS detector at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 35.9 fb

$^{-1}$ .

The result targets previously unexplored

${\mathrm{t\bar{t}}\mathrm{H}}$ production mode. The combination yields an observed (expected) upper limit for the branching fraction of invisible Higgs boson decays of

${\mathcal{B}({\mathrm{H}\to\mathrm{inv}} )} <$ 0.46 (0.48) at the 95% CL for a Higgs boson mass of 125 GeV. Under the assumption of Standard Model like production cross section, the constraint is weaker than direct limits obtained using the vector boson fusion topology, comparable with those obtained using the associated production, and stronger than the gluon fusion limits [50]. Furthermore, the

${\mathrm{t\bar{t}}\mathrm{H}}$ mode can have highest sensitivity to beyond Standard Model scenarios with enhanced top quark Yukawa couplings, and therefore provides comlementary information to the vector boson fusion topology based searches. The result is currently statistically limited due to the low cross section of the

${\mathrm{t\bar{t}}\mathrm{H}}$ process and will strongly benefit from updates with more data.

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