First-hand information for everyone
Researchers with the CMS experiment at the Large Hadron Collider looked for a rare process in which a Higgs boson is produced together with two vector bosons (the W or Z bosons) through a mechanism called vector boson scattering. They used collision data collected at a center-of-mass energy of 13 TeV from 2016–2018, corresponding to an integrated luminosity of 138 inverse femtobarns. The search tests the strength of the four-particle interaction between two vector bosons and two Higgs bosons, expressed as a coupling modifier called κ2V (kappa-two-V).
The analysis selects events that look like vector boson scattering: two jets far forward in the detector (the VBS signature) plus a Higgs boson that decayed to a pair of bottom quarks. Because the Higgs and at least one vector boson are often produced with high momentum here, their decay products tend to merge into single, large-radius jets. The team therefore reconstructs the Higgs as a single large jet tagged for two b quarks and categorizes events by how many charged leptons (electrons or muons) are present: zero, one, or two. They combine simulations of the signal and many backgrounds with data-driven methods to predict the remaining background in the signal region.
Quantitatively, the Standard Model prediction for the VBS production of VVH at 13 TeV is small, about 1.99 femtobarns at leading order (a femtobarn corresponds to a very small probability for the process). The CMS search excludes at 95% confidence level values of the coupling modifier κ2V outside the interval 0.40 < κ2V < 1.60 (observed), with an expected exclusion of 0.34 < κ2V < 1.66, when all other couplings are fixed to their Standard Model values. The analysis also sets constraints on the separate WWHH and ZZHH coupling modifiers (κ2W and κ2Z) and on the allowed region in the κ2W–κ2Z plane.
This result matters because it provides a new way to probe the quartic interaction between two vector bosons and two Higgs bosons, an interaction that had been probed mostly through searches for Higgs boson pair production until now. Deviations of κ2V from its Standard Model value of 1 would both increase the production rate and make the final-state particles more energetic, which helps experimental sensitivity. The CMS limits are therefore complementary to previous limits from Higgs pair searches.
Important caveats accompany the result. The process is very rare, so the measurement is statistically limited and sensitive to how well backgrounds are modeled. The search assumes the Higgs self-coupling (denoted κλ) takes its Standard Model value (κλ = 1); changes in that coupling were not explored here because they have a smaller effect on this channel. The analysis also focuses on events with a boosted Higgs decaying to bottom quarks and on the VBS topology, so it does not cover all possible final states. Finally, the quoted production rate is a leading-order theoretical prediction and the study relies on a mix of simulation and data-driven background estimates, with the largest background in the all-hadronic channel coming from ordinary jets produced by quantum chromodynamics processes.