Model-independent bounds on R(J/ψ)

A bstract We present a model-independent bound on R J / ψ ≡ ℬ ℛ B C + → J / ψ τ + ν τ / ℬ ℛ B C + → J / ψ µ + ν µ . This bound is constructed by constraining the form factors through a combination of dispersive relations, heavy-quark relations at zero-recoil, and the limited existing determinations from lattice QCD. The resulting 95% confidence-level bound, 0.20 ≤ R ( J / ψ ) ≤ 0.39, agrees with the recent LHCb result at 1.3 σ , and rules out some previously suggested model form factors.