A measurement of the ratio of light-lepton inclusive semileptonic $B$ decay rates $R (X_{e / μ})$ = $B (B \to X e ν)$ / $B (B \to X μ ν)$ using $189 {fb}^{- 1}$ of data at Belle~II

Sumitted to PubDB: 2023-02-01

Category: Proceeding, Visibility: Public

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Authors	Henrik Junkerkalefeld
Date	2022-12-16
Belle II Number	BELLE2-CONF-PROC-2023-006
Abstract	In this work a measurement of the ratio of branching fractions of inclusive semileptonic $B$ meson decays, $R (X_{e / μ}) = B (B \to X e ν) / B (B \to X μ ν)$ is reported as a probe of $e - μ$ universality. Electron-positron collisions collected at the $Υ (4 S)$ resonance with the Belle II detector corresponding to $189 {fb}^{- 1}$ of integrated luminosity are used. One $B$ meson is reconstructed in its fully hadronical decays, while the semileptonic $B$ meson decay is selected by demanding the reconstructed lepton to have a momentum in the $B$ rest frame above $1.3 GeV / c$ . We find $R (X_{e / μ}) = 1.033 \pm 0.010 \pm 0.019$ . The first contribution to the uncertainty is statistical, the second systematic. This is the most precise branching-fraction based test of $e - μ$ universality in semileptonic $B$ decays to date and agrees with the Standard Model expectation within $1.3 σ$ .

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