B→K 1 ℓ + ℓ − decays in a family non-universal Z′ model

Abstract

The implications of the family non-universal Z′ model in the B→K 1(1270,1400)ℓ + ℓ −(ℓ=e ,μ ,τ) decays are explored, where the mass eigenstates K 1(1270, 1400) are the mixtures of 1 P 1 and 3 P 1 states with the mixing angle θ. In this work, considering the Z′ boson and setting the mixing angle θ=(−34±13)○, we analyze the branching ratio, the dilepton invariant mass spectrum, the normalized forward–backward asymmetry and lepton polarization asymmetries of each decay mode. We find that all observables of B→K 1(1270)μ + μ − are sensitive to the Z′ contribution. Moreover, the observables of B→K 1(1400)μ + μ − have a relatively strong θ-dependence; thus, the Z′ contribution will be buried by the uncertainty of the mixing angle θ. Furthermore, the zero crossing position in the FBA spectrum of B→K 1(1270)μ + μ − at low dilepton mass will move to the positive direction with Z′ contribution. For the tau modes, the effects of Z′ are not remarkable due to the small phase space. These results could be tested in the running LHC-b experiment and Super-B factory.