부산대학교 도서관

Abstract We present a model-independent prediction for R(η c )≡ℬℛ(B c + → η c τ + ν τ )/ℬℛ(B c + → η c µ + ν µ ). 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(η c ) = 0.29(5), agrees with previous model predictions, but without uncontrolled systematic uncertainties.