Y and ψ leptonic decays as probes of solutions to the R(D (*)) puzzle

Abstract

Experimental measurements of the ratios R(D(∗))≡Γ(B→D(*)τv)Γ(B→D(*)ℓv)(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 bb¯ → τ+τ− and/or cc¯ → τ+τ− transitions. These contributions lead to violation of lepton flavor universality in, respectively, Y 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 Y(1S, 2S, 3S) → ττ in the upcoming Belle II experiment.