Electroweak effects in the double Dalitz decay Bs→l+l−l′+l′−

We investigate the double Dalitz decays Bs→l+l−l′+l′− on the basis of the effective Hamiltonian for the transition bs̄→l+l−, and universal form factors suggested by QCD. The correlated mass spectrum of the two lepton pairs in the decay Bs→e+e−μ+μ− is derived in an efficient way, using a QED result for meson decays mediated by two virtual photons: Bs→γ∗γ∗→e+e−μ+μ−. A comment is made on the correlation between the planes of the two lepton pairs. The conversion ratios ρlll′l′=Γ(Bs→l+l−l′+l′−)Γ(Bs→γγ) are estimated to be ρeeee=3×10−4,ρeeμμ=9×10−5 and ρμμμμ=3×10−5, and are enhanced relative to pure QED by 10–30%.