Search for Higgs bosons decaying into new spin-0 or spin-1 particles in four-lepton final states with the ATLAS detector with 139 fb−1 of pp collision data at $$ \sqrt{s} $$ = 13 TeV

Abstract

Searches are conducted for new spin-0 or spin-1 bosons using events where a Higgs boson with mass 125 GeV decays into four leptons (ℓ = e, μ). This decay is presumed to occur via an intermediate state which contains two on-shell, promptly decaying bosons: H → XX/ZX → 4ℓ, where the new boson X has a mass between 1 and 60 GeV. The search uses pp collision data collected with the ATLAS detector at the LHC with an integrated luminosity of 139 fb−1 at a centre-of-mass energy $$ \sqrt{s} $$ s = 13 TeV. The data are found to be consistent with Standard Model expectations. Limits are set on fiducial cross sections and on the branching ratio of the Higgs boson to decay into XX/ZX, improving those from previous publications by a factor between two and four. Limits are also set on mixing parameters relevant in extensions of the Standard Model containing a dark sector where X is interpreted to be a dark boson.

Review on Higgs Hidden–Dark Sector Physics at High-Energy Colliders

“…The decay H→ZZd probes the parameter space of ε and mZd for the processes outlined in this study [34] and is independent of the occurrence of mixing between the SM Higgs boson and the dark-sector Higgs boson, κ. On an event-by-event basis, however, this BSM signal is indistinguishable from SM H→ZZ and hence must originate as a resonance in the dilepton mass above this background process.…”

“…The Higgs mixing parameter κ is constrained by the Η→ΖdZd→4l search. ATLAS has undertaken a search [34] for new spin 0 or spin 1 bosons utilizing events in which a 125 GeV Higgs boson decays to four leptons (l = e, μ). This decay is αssumed to take place through an intermediate state containing two on-shell, rapidly decaying bosons: H→XX/ZX→4l, where the new boson X has a mass of 1 to 60 GeV.…”

“…This ATLAS study [34] describes three searches for an SM Higgs boson H decaying via a new boson to a final state comprised of four charged leptons (l ≡ e, μ). The new boson might be a dark sector vector boson or a scalar boson, labeled X, according to the models that underpin these analyses.…”

“…These searches should be sensitive to any intermediate bosons that are narrow, on-shell, and decay quickly within the mass ranges investigated. This ATLAS publication [34] provides model-independent fiducial cross section limits as well as model-specific limits.…”

“…Two well-motivated "benchmark models" for exotic decays to "light BSM" bosons are summarized below and utilized to understand the results in the publication [34]. The SM is extended with a dark-sector U(1) group, abbreviated U(1)d, in the first BSM benchmark model, resulting in the development of a BSM vector boson, Zd.…”