Abstract
In this work we evaluate the long-distance QED contributions, induced by the magnetic-dipole corrections to the final charged leptons, on the B meson decay widths B → (K, K*)ℓ+ℓ− and ratios RK,K* = Γ(B → (K, K*)μ+μ−)/Γ(B → (K, K*)e+e−), as well as on \( {R}_{K,K\ast}^{\tau } \) (with μ replaced by the τ lepton). QED long-distance contributions induced by the Coulomb potential corrections (Fermi-Sommerfeld factors) were also included. Corresponding corrections to the inclusive decay widths of B → Xsℓ+ℓ−, with ℓ = e, μ, τ, are also analyzed for completeness. The magnetic-dipole corrections, which are manifestly Lepton Flavor Universality violating and gauge-invariant, are expected to be particularly enhanced in RK* for the dilepton mass region close to the threshold. However, we find that the largest contribution of all these corrections to the RK,K* observables do not exceed a few per mille effect, thus reinforcing the validity of previous estimates about the leading QED corrections to RK,K*. Finally, viable new physics contributions to RK,K* induced by the exchange of a massless dark-photon via magnetic-dipole interactions, which provide the leading contribution to the corresponding B → (K, K*)ℓ+ℓ− amplitudes in this scenario, are analyzed in light of the present RK,K* anomalies.
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Gabrielli, E., Palmiotto, M. Magnetic-dipole corrections to RK and RK* in the Standard Model and dark photon scenarios. J. High Energ. Phys. 2020, 145 (2020). https://doi.org/10.1007/JHEP10(2020)145
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DOI: https://doi.org/10.1007/JHEP10(2020)145