Kavli Affiliate: T. Higuchi
| First 5 Authors: , , , ,
| Summary:
We report measurements of the ratios of branching fractions $cal
R(D^(*)+) = fraccal B(overlineB^0 to D^(*)+ ,tau^- ,
overlinenu_tau)cal B(overlineB^0 to D^(*)+ , ell^- ,
overlinenu_ell)$, where $ell$ denotes either an electron or a muon.
These ratios test the universality of the charged-current weak interaction. The
results are based on a $365, mathrmfb^-1$ 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 $Upsilon(4S)$ resonance, just above
the threshold for $BoverlineB$ production. Signal candidates are
reconstructed by selecting events in which the companion $B$ meson from the
$Upsilon(4S) to BoverlineB$ decay is identified in semileptonic modes.
The $tau$ lepton is reconstructed via its leptonic decays. We obtain $cal
R(D^+) = 0.418 pm 0.074 ~(mathrmstat) pm 0.051 ~(mathrmsyst)$ and
$cal R(D^*+) = 0.306 pm 0.034 ~(mathrmstat) pm 0.018
~(mathrmsyst)$, 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.
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