mass energy corresponding to the Υ(4𝑆) resonance. These data, characterised by low particlemultiplicity, well-constrained initial-state kinematics, and excellent lepton identification, providean ideal environment to study lepton-flavour universality in semileptonic 𝐵 decays. We presentresults on the ratios of semitauonic decay rates compared to those to light leptons in both exclusiveand inclusive 𝐵 decay. These include new measurements of the ratios for exclusive 𝐵 → 𝐷(∗) ℓ𝜈ℓdecays 𝑅(𝐷(∗))𝜏/ℓ in events tagged by a semileptonic 𝐵 decay.
M. Mantovano (Wed,) studied this question.