We measure the tau-to-light-lepton ratio of inclusive B-meson branching fractions R ( X tau= l ) equivalent to B ( B-* X tau nu ) = B ( B-* X l nu ) , where l indicates an electron or muon, and thereby test the universality of charged-current weak interactions. We select events that have one fully reconstructed B meson and a charged lepton candidate from 189 fb-1 - 1 of electron-positron collision data collected with the Belle II detector. We find R ( X tau= l ) = 0.228 + 0.016(stat) ( stat ) + 0.036(syst), ( syst ) , in agreement with standard-model expectations. This is the first direct measurement of R ( X tau= l ) .
First Measurement of $R(X_{τ/\ell})$ as an Inclusive Test of the $b \to c τν$ Anomaly
A. Gaz;R. Stroili;
2023
Abstract
We measure the tau-to-light-lepton ratio of inclusive B-meson branching fractions R ( X tau= l ) equivalent to B ( B-* X tau nu ) = B ( B-* X l nu ) , where l indicates an electron or muon, and thereby test the universality of charged-current weak interactions. We select events that have one fully reconstructed B meson and a charged lepton candidate from 189 fb-1 - 1 of electron-positron collision data collected with the Belle II detector. We find R ( X tau= l ) = 0.228 + 0.016(stat) ( stat ) + 0.036(syst), ( syst ) , in agreement with standard-model expectations. This is the first direct measurement of R ( X tau= l ) .
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