Genuine lepton-flavor-universality-violating observables in the τ−μ sector of B→(K,K*)ℓℓ decays

Abstract

It was previously shown that unlike the ratios RKμe≡RK≡Γ(B→Kμ+μ−)/Γ(B→Ke+e−) and RK*μe≡RK*≡Γ(B→K*μ+μ−)/Γ(B→K*e+e−), the ratios RKτμ and RK*τμ can deviate from their Standard Model (SM) predictions even with universal new physics couplings. This observation highlights the critical need to identify and establish genuine lepton flavor universality violating (LFUV) observables in the τ−μ sector. This work embarks on establishing genuine LFUV ratio observables in B→Kℓℓ and B→K*ℓℓ decays through comprehensive analysis of their angular distributions. We find that like RK*τμ, the ratios RAFBτμ and RfLτμ do not qualify as genuine LFUV observables, whereas the ratios of all optimized observables in B→K*ℓℓ decays within the τ−μ sector definitively do. In the case of B→Kℓℓ decays, similar to RKτμ, the ratio RFH is influenced by mass effects and therefore cannot be considered a genuine LFUV observable in the τ−μ sector. However, the ratio Γτ(1−FHτ)/Γμ(1−FHμ) stands as the sole genuine LFUV observable in B→Kℓℓ decays. Furthermore, by making use of new physics Lorentz structures which provide a better fit to the current b→sℓℓ data as compared to the SM, we demonstrate how the nongenuine LFUV ratios RAFBτμ and RfLτμ can be employed to distinguish between framework with solely universal lepton couplings and those with both universal and nonuniversal couplings. Published by the American Physical Society 2024