2025/04/15 by Belle II Collaboration, Adachi, I., Adamczyk, K. +450 · 1 citation
#FOS: Physical sciences #High Energy Physics - Experiment (hep-ex)
paper · doi:10.48550/arxiv.2504.11220
We report measurements of the ratios of branching fractions \cal R(D(*)+) = \frac\cal B(B0 → D(*)+ τ- ντ)\cal B(B0 → D(*)+ ℓ- ν_ℓ), where ℓ denotes either an electron or a muon. These ratios test the universality of the charged-current weak interaction. The results are based on a 365 fb-1 data sample collected with the Belle II detector at the SuperKEKB e+e- collider, which operates at a center-of-mass energy corresponding to the Υ(4S) resonance, just above the threshold for BB production. Signal candidates are reconstructed by selecting events in which the companion B meson from the Υ(4S) → BB decay is identified in semileptonic modes. The τ lepton is reconstructed via its leptonic decays. We obtain \cal R(D+) = 0.418 ± 0.074 ~(stat) ± 0.051 ~(syst) and \cal R(D*+) = 0.306 ± 0.034 ~(stat) ± 0.018 ~(syst), which are consistent with world average values. Accounting for the correlation between them, these values differ from the Standard Model expectation by a collective significance of 1.7 standard deviations.