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

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 $$ \mathcal{O} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>O</mml:mi> </mml:math> (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 ′ ( &lt; 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 $$ {m}_{Z^{\prime }} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>m</mml:mi> <mml:msup> <mml:mi>Z</mml:mi> <mml:mo>′</mml:mo> </mml:msup> </mml:msub> </mml:math> ≲ 10 GeV.