Publikace na Matematicko-fyzikální fakulta |
2023
Abstrakt
We present the first measurement of the ratio of branching fractions of inclusive semileptonic B-meson decays, R(X-e/mu) = B(B -> Xe nu)/B(B -> X mu nu), a precision test of electron-muon universality, using data corresponding to 189 fb(-1) from electron-positron collisions collected with the Belle II detector. In events where the partner B meson is fully reconstructed, we use fits to the lepton momentum spectra above 1.3 GeV/c to obtain R(X-e/mu) = 1.007 +/- 0.009(stat) +/- 0.019(syst), which is the most precise lepton-universality test of its kind and agrees with the standard-model expectation.