Υ and ψ leptonic decays as probes of solutions to the R(D^(∗)) puzzle

Experimental measurements of the ratios R(D^(∗))≡((Γ(B→D^(∗)τν))/(Γ(B→D^(∗)ℓν))) (ℓ=e,μ) show a 3.9σ deviation from the Standard Model prediction. In the absence of light right-handed neutrinos, a new physics contribution to b→cτν decays necessarily modifies also bb̄→τ⁺τ⁻ and/or cc̄→τ⁺τ⁻ transitions. These contributions lead to violation of lepton flavor universality in, respectively, Υ and ψ leptonic decays. We analyze the constraints resulting from measurements of the leptonic vector-meson decays on solutions to the R(D^(∗)) puzzle. Available data from BaBar and Belle can already disfavor some of the new physics explanations of this anomaly. Further discrimination can be made by measuring Υ(1S,2S,3S)→ττ in the upcoming Belle II experiment.