CMS-HIG-23-006

CMS-HIG-23-006 ; CERN-EP-2024-145
Constraints on the Higgs boson self-coupling with combination of single and double Higgs boson production
CMS Collaboration
18 July 2024
Accepted for publication in Phys. Lett. B
Abstract: A combination of Higgs boson (H) measurements and searches for the production of Higgs boson pairs (HH) is presented, aiming to constrain the H trilinear self-coupling $ \lambda_3 $, using the proton-proton collision data collected by the CMS experiment at $ \sqrt{s} = $ 13 TeV. The cross sections of the main H production modes and the branching ratios of the principal decay channels depend on $ \lambda_3 $ because of next-to-leading-order electroweak corrections. The cross sections of the HH production via gluon fusion and via vector boson fusion depend on $ \lambda_3 $ as well as on the H couplings to the top quark, and to vector bosons, respectively. The combination of event categories enriched in single-H and HH events allows the extraction of constraints on $ \kappa_\lambda $, defined as the value of $ \lambda_3 $ normalized to its standard model prediction, with fewer assumptions on the H couplings to the fermions and vector bosons. Values of $ \kappa_\lambda $ outside the interval $ -1.2 < \kappa_\lambda < 7.5 $ are excluded at 95.4% confidence level, which is compatible with the expected range of $ -2.0 < \kappa_\lambda < 7.7 $ under the assumption that all the other H couplings are equal to their standard model predicted values.
Links: e-print arXiv:2407.13554 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; Physics Briefing ; CADI line (restricted) ;

Figures & Tables	Summary	Additional Tables	References	CMS Publications

Figures
png pdf	Figure 1: Observed profiled likelihood scans of $ \kappa_\lambda $ comparing the full combination of single-H and HH (orange) to the combinations of only single-H (blue) or only HH (green) channels.
png pdf	Figure 2: Observed two-dimensional likelihood scans of $ (\kappa_\lambda, k_{\mathrm{T}}) $ comparing the full combination of single-H and HH (orange) to the combinations of only single-H (blue) or only HH (green) channels.
png pdf	Figure 3: Observed two-dimensional likelihood scans of $ (\kappa_\mathrm{V}, \kappa_{2\mathrm{V}}) $ comparing the full combination of single-H and HH (orange) to the combinations of only single-H (blue) or only HH (green) channels. The best fit point for the single-H combination can not be calculated because this combination has no sensitivity on the $ \kappa_{2\mathrm{V}} $ parameter.
png pdf	Figure 4: Observed likelihood scans of $ \kappa_\lambda $ assuming $ \kappa_\mathrm{V} $, $ \kappa_{2\mathrm{V}} $, $ k_{\mathrm{T}} $, $ \kappa_\mathrm{b} $, $ \kappa_\tau $, and $ \kappa_\mu $ as unconstrained nuisance parameters.

Tables
png pdf	Table 1: Analyses targeting single-H production modes and decay channels included in the combination and the corresponding data set size, in terms of integrated luminosity. The maximum phase space granularity of each cross section measurement is also reported.
png pdf	Table 2: Analyses targeting HH searches included in this combination and the corresponding HH production modes targeted with dedicated categories.
png pdf	Table 3: Expected and observed constraints on $ \kappa_\lambda $ at 95.4% confidence levels and best fit values from the combination of the single-H and HH channels under different assumptions on the Higgs boson couplings to fermions and vector bosons.

Summary

The combination of single Higgs boson (H) measurements and searches for Higgs boson pair production (HH) to constrain the Higgs boson trilinear self-coupling, is presented in this document. Proton-proton collision data at $ \sqrt{s} = $ 13 TeV, collected by the CMS experiment between 2016 and 2018, were analyzed. This is the first combination of single-H and HH channels at the CMS experiment. The complementarity of the constraints on the Higgs boson couplings of the single-H and HH channels is exploited in the combination. The inclusion of the single-H channels improves the constraints on $ \kappa_\lambda $ under minimal assumptions on the Higgs boson couplings to fermions and vector bosons. The observed (expected) confidence interval at 95.4% on $ \kappa_\lambda $ assuming the other Higgs boson couplings fixed to the SM prediction, is found to be $ -1.2 < \kappa_\lambda < 7.5 $ ($ -2.0 < \kappa_\lambda < 7.7 $). Under minimal assumptions on the Higgs boson couplings to fermions and vector bosons, the observed (expected) exclusion interval at 95.4% on $ \kappa_\lambda $ is $ -2.3 < \kappa_\lambda < 7.8 $ ($ -1.4 < \kappa_\lambda < 7.8 $).

Additional Tables

png pdf

Additional Table 1:
Summary of overlaps between the considered single-H and HH analyses included in this combination. Non-overlapping analyses are indicated by a $ \checkmark $, overlaps removable with negligible impact on the combination are indicated by a $\mathcal{X}$. The single-H analyses are orthogonal to each other. Also the HH analyses are found to be orthogonal to each other, with the only exception of $ \mathrm{H}\mathrm{H} \to \mathrm{b}\overline{\mathrm{b}}\mathrm{b}\overline{\mathrm{b}} (\mathrm{V}\mathrm{H}\mathrm{H}) $.

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