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Evidence of off-shell Higgs boson production from ZZ leptonic decay channels and constraints on its total width with the ATLAS detector

Research output: Contribution to Journal/MagazineJournal articlepeer-review

  • ATLAS Collaboration
Article number138223
<mark>Journal publication date</mark>10/11/2023
<mark>Journal</mark>Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics
Publication StatusPublished
Early online date13/10/23
<mark>Original language</mark>English


This Letter reports on a search for off-shell production of the Higgs boson using 139 fb −1 of pp collision data at s= 13 TeV collected by the ATLAS detector at the Large Hadron Collider. The signature is a pair of Z bosons, with contributions from both the production and subsequent decay of a virtual Higgs boson and the interference of that process with other processes. The two observable final states are ZZ→4ℓ and ZZ→2ℓ2ν with ℓ=e or μ. In the ZZ→4ℓ final state, a dense Neural Network is used to enhance analysis sensitivity with respect to matrix element-based discrimination. The background-only hypothesis is rejected with an observed (expected) significance of 3.3 (2.2) standard deviations, representing experimental evidence for off-shell Higgs boson production. Assuming that no new particles enter the production of the virtual Higgs boson, its total width can be deduced from the measurement of its off-shell production cross-section. The measured total width of the Higgs boson is 4.5 −2.5 +3.3 MeV, and the observed (expected) upper limit on the total width is found to be 10.5 (10.9) MeV at 95% confidence level.