Abstract
We present a model-independent bound on \( R\left(J/\psi \right)\equiv \mathrm{\mathcal{B}}\mathrm{\mathcal{R}}\left({B}_C^{+}\to J/\psi {\tau}^{+}{\nu}_{\tau}\right)/\mathrm{\mathcal{B}}\mathrm{\mathcal{R}}\left({B}_C^{+}\to J/\psi {\mu}^{+}{\nu}_{\mu}\right) \). 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 1.3σ, and rules out some previously suggested model form factors.
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Cohen, T.D., Lamm, H. & Lebed, R.F. Model-independent bounds on R(J/ψ). J. High Energ. Phys. 2018, 168 (2018). https://doi.org/10.1007/JHEP09(2018)168
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DOI: https://doi.org/10.1007/JHEP09(2018)168