A test of lepton flavor universality with a measurement of R(D^*) using hadronic B tagging at the Belle II experiment

2024/01/05 by Belle II Collaboration, Adachi, I., Adamczyk, K. +434 · 3 citations
#FOS: Physical sciences #High Energy Physics - Experiment (hep-ex)

paper · doi:10.48550/arxiv.2401.02840

Abstract

The ratio of branching fractions R(D^*) = B(B → D^* τ^- ν_τ)/B (B → D^* ℓ^- ν_ℓ), where ℓ is an electron or muon, is measured using a Belle~II data sample with an integrated luminosity of 189~fb^-1 at the SuperKEKB asymmetric-energy e⁺ e^- collider. Data is collected at the Υ(4S) resonance, and one B meson in the Υ(4S)→ BB decay is fully reconstructed in hadronic decay modes. The accompanying signal B meson is reconstructed as B→ D^* τ^-ν_τ using leptonic τ decays. The normalization decay, B→ D^* ℓ^- ν_ℓ, where ℓ is an electron or muon, produces the same observable final state particles. The ratio of branching fractions is extracted in a simultaneous fit to two signal-discriminating variables in both channels and yields R(D^*) = 0.262~_-0.039^+0.041(stat)~_-0.032^+0.035(syst). This result is consistent with the current world average and with standard model predictions.

Cited by

• Joint LHCb–Belle II prospects to constrain new physics in B→ D^(*)τ ν
• Searches for B⁰→ K⁺π^-τ⁺τ^- and B_s⁰→ K⁺K^-τ⁺τ^- decays
• Flavour Physics Beyond the Standard Model

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