On-shell Higgs boson production at colliders only measures narrow resonance properties; measuring off-shell Higgs production at high invariant mass decouples the Higgs width, enabling precision tests of Higgs compositeness and top Yukawa couplings.
Since its discovery in 2012 at CERN's Large Hadron Collider, the Higgs boson has verified how fundamental particles acquire mass, yet its total decay width is so narrow () that detector resolution cannot measure it directly.
On-shell collision measurements only constrain the product of Higgs production cross-sections and decay branching ratios, allowing hypothetical beyond-Standard-Model physics to hide through compensatory parameter shifts.
This high-energy physics paper establishes global precision benchmarks using off-shell Higgs boson production, where the Higgs is produced at invariant masses far above 125 GeV. Measuring off-shell interference in four-lepton and channels directly constrains the Higgs total width and tests for anomalous top Yukawa and self-coupling deviations.
Precision off-shell Higgs measurements transform the LHC into a powerful probe of Higgs compositeness and electroweak symmetry breaking, searching for subtle cracks in the Standard Model.
Off-shell Higgs boson measurements: Yukawa couplings, self-coupling, compositeness, and width
Measurements of Higgs boson production in the off-shell region are presented, using the four-lepton decay channel. Data from proton-proton collisions at the CERN LHC, collected by the CMS experiment and corresponding to an integrated luminosity of 138 fb at a center-of-mass energy of 13 TeV, are utilized. The first direct test of composite Higgs boson models is performed, with a lower limit on the compositeness scale set at 870 GeV at the 95% confidence level. Tests of gluon-fusion production within the standard model effective field theory framework are performed. The first constraint on the Higgs boson self-coupling in the off-shell region is obtained. By combining on- and off-shell measurements, the analysis sets the tightest constraints to date on light-quark Yukawa couplings, while relaxing assumptions such as the bound on the Higgs boson coupling to vector bosons, thereby providing more model-independent results. Constraints on the Higgs boson width are provided while accounting for a range of beyond-the-standard-model effects, including both light and heavy particles in the gluon-fusion production loop, as well as modified couplings to vector bosons. A combined analysis of the HZZ and PHWW channels is performed to improve sensitivity to the Higgs boson width, yielding = 5.1 MeV. The scenario of no off-shell Higgs boson production is excluded at a confidence level exceeding 5 standard deviations.
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