Test of lepton flavor universality with measurements of and using semileptonic tagging at the Belle II experiment
Physical Review D, 2025•APS
We report measurements of the ratios of branching fractions R (D (*)+)= B (B¯ 0→ D (*)+ τ-ν¯
τ)/B (B¯ 0→ 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 (4 S) resonance, just above the
threshold for BB¯ production. Signal candidates are reconstructed by selecting events in …
τ)/B (B¯ 0→ 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 (4 S) resonance, just above the
threshold for BB¯ production. Signal candidates are reconstructed by selecting events in …
We report measurements of the ratios of branching fractions R(D(*)+)=B(B¯0→D(*)+τ-ν¯τ)/B(B¯0→D(*)+ℓ-ν¯ℓ), where denotes either an electron or a muon. These ratios test the universality of the charged-current weak interaction. The results are based on a data sample collected with the Belle II detector at the SuperKEKB collider, which operates at a center-of-mass energy corresponding to the ϒ(4S) resonance, just above the threshold for production. Signal candidates are reconstructed by selecting events in which the companion meson from the ϒ(4S)→BB¯ decay is identified in semileptonic modes. The lepton is reconstructed via its leptonic decays. We obtain and , 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.