Search for new light gauge bosons in Higgs boson decays to four-lepton final states in pp collisions at √s = 8 TeV with the ATLAS detector at the LHC

Abstract

This paper presents a search for Higgs bosons decaying to four leptons, either electrons or muons, via one or two light exotic gauge bosons Z[subscript d], H → ZZ[subscript d] → 4ℓ or H → Z[subscript d]Z[subscript d] → 4ℓ. The search was performed using pp collision data corresponding to an integrated luminosity of about 20 fb[superscript −1] at the center-of-mass energy of √s = 8 TeV recorded with the ATLAS detector at the Large Hadron Collider. The observed data are well described by the Standard Model prediction. Upper bounds on the branching ratio of H → ZZ[subscript d] → 4ℓ and on the kinetic mixing parameter between the Z[subscript d] and the Standard Model hypercharge gauge boson are set in the range (1–9) × 10[superscript −5] and (4–17) × 10[superscript −2] respectively, at 95% confidence level assuming the Standard Model branching ratio of H → ZZ[superscript ∗] → 4ℓ, for Z[subscript d] masses between 15 and 55 GeV. Upper bounds on the effective mass mixing parameter between the Z and the Z[subscript d] are also set using the branching ratio limits in the H → ZZ[subscript d] → 4ℓ search, and are in the range (1.5–8.7) × 10[superscript −4] for 15 < mZ[subscript d] < 35 GeV. Upper bounds on the branching ratio of H → Z[subscript d]Z[subscript d] → 4ℓ and on the Higgs portal coupling parameter, controlling the strength of the coupling of the Higgs boson to dark vector bosons are set in the range (2–3) × 10[superscript −5] and (1–10) × 10[superscript −4] respectively, at 95% confidence level assuming the Standard Model Higgs boson production cross sections, for Z[subscript d] masses between 15 and 60 GeV.