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

Abstract

Abstract Experimental measurements of the ratios R D ∗ ≡ Γ B → D * τ v Γ B → D * ℓ v ℓ = e , μ $$ R\left({D}^{\left(\ast \right)}\right)\equiv \frac{\Gamma \left(B\to {D}^{\left(*\right)}\tau v\right)}{\Gamma \left(B\to {D}^{\left(*\right)}\ell v\right)}\left(\ell =e,\mu \right) $$ 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 b b ¯ → τ + τ − $$ b\overline{b}\to {\tau}^{+}{\tau}^{-} $$ and/or c c ¯ → τ + τ − $$ c\overline{c}\to {\tau}^{+}{\tau}^{-} $$ 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.

Keywords

• Beyond Standard Model
• Heavy Quark Physics
• Precision QED