Multi-lepton jets from quadruple Z′ via the Higgs decay at LHC

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A bstract We investigate multi-lepton jet events from the decay of the 125 GeV Higgs boson ( h ) into quadruple new gauge bosons ( Z ′) at the LHC. Such an exotic decay is realized via the process of h → ϕϕ → Z ′ Z ′ Z ′ Z ′ with new scalar boson ϕ in models with an additional U(1) gauge symmetry. Charged leptons coming from the Z ′ decay tend to be observed as lepton-jets rather than isolated leptons when the masses of Z ′ and ϕ are smaller than O O (10) GeV, because of the highly-boosted effects. Performing the signal and background analyses, we find that the branching ratio of h → 4 Z ′ is maximally constrained to be smaller than of order 10 − 6 (10 − 7 ) by using the muonic-lepton jets assuming the integrated luminosity of 140 fb − 1 (3000 fb − 1 ) at LHC. For lighter Z ′ ( < 2 m μ ), we can use the electronic-lepton jets instead of the muon-jets, by which the upper limit on the branching ratio is obtained to be of order 10 − 6 –10 − 5 . These bounds can be converted into the constraint on model parameters such as a mixing angle between h and ϕ . It is shown that stronger bounds on the mixing angle are obtained in the dark photon case as compared with the previous constraints given by flavor experiments and the Higgs decay h → Z ′ Z ′ in the mass range of m_Z m Z ′ ≲ 10 GeV.