Abstract
We present a model-independent prediction for R(ηc)≡ℬℛ(B +c → ηcτ+ντ)/ℬℛ(B +c → ηcµ+νµ). This prediction is obtained from 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 prediction, R(ηc) = 0.29(5), agrees with previous model predictions, but without uncontrolled systematic uncertainties.
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Berns, A., Lamm, H. Model-independent prediction of R(ηc). J. High Energ. Phys. 2018, 114 (2018). https://doi.org/10.1007/JHEP12(2018)114
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DOI: https://doi.org/10.1007/JHEP12(2018)114