Measurement of R (D) and R (D?) with a Semileptonic Tagging Method
Journal
Physical Review Letters
Journal Volume
124
Journal Issue
16
Date Issued
2020
Author(s)
Caria G. et al. (Belle Collaboration)
Abstract
The experimental results on the ratios of branching fractions R(D)=B(B→Dτ-ντ)/B(B→D?-ν?) and R(D?)=B(B→D?τ-ντ)/B(B→D??-ν?), where ? denotes an electron or a muon, show a long-standing discrepancy with the standard model predictions, and might hint at a violation of lepton flavor universality. We report a new simultaneous measurement of R(D) and R(D?), based on a data sample containing 772×106 BB events recorded at the ?(4S) resonance with the Belle detector at the KEKB e+e- collider. In this analysis the tag-side B meson is reconstructed in a semileptonic decay mode and the signal-side τ is reconstructed in a purely leptonic decay. The measured values are R(D)=0.307±0.037±0.016 and R(D?)=0.283±0.018±0.014, where the first uncertainties are statistical and the second are systematic. These results are in agreement with the standard model predictions within 0.2, 1.1, and 0.8 standard deviations for R(D), R(D?), and their combination, respectively. This work constitutes the most precise measurements of R(D) and R(D?) performed to date as well as the first result for R(D) based on a semileptonic tagging method. ? 2020 authors.
Subjects
Atomic physics; Physics; Belle detectors; Branching fractions; Measured values; Precise measurements; Semileptonic decay; Simultaneous measurement; Standard deviation; The standard model; High energy physics; article; meson; prediction; uncertainty
Type
journal article