Aad, G.Abbott, B.Abeling, K.Abidi, S. H.Aboulhorma, A.Abramowicz, H.Çetin, Serkant Ali2024-05-192024-05-1920230370-26931873-2445https://doi.org10.1016/j.physletb.2023.138223https://hdl.handle.net/20.500.12713/5731This Letter reports on a search for off-shell production of the Higgs boson using 139 fb(-1) of pp collision data at root 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 Z Z -> 2l2 nu with l = e or mu. 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. (c) 2023 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).eninfo:eu-repo/semantics/openAccessW+WArticle846WOS:0011253803000012-s2.0-85174896283N/A10.1016/j.physletb.2023.138223Q1