Measurement of the Ratio ${\cal B}\xspace(\B^+ \to X e \nu)$ / ${\cal B}\xspace(\B^0 \to X e \nu)

TL;DR

This study measures the inclusive electron spectra in charged and neutral B meson decays and determines the ratio of their semileptonic branching fractions using a large dataset from the Belle detector.

Contribution

It provides the first precise measurement of the ratio of semileptonic branching fractions between charged and neutral B mesons.

Findings

The ratio ${ m{f B}}^+ o X e u$ / ${ m{f B}}^0 o X e u$ is measured to be 1.084 ± 0.041 (stat) ± 0.025 (syst).

The analysis uses a large dataset of 231 million B meson pairs from the Belle experiment.

The method involves fully reconstructing one B meson and identifying electrons from the other B meson.

Abstract

We report measurements of the inclusive electron momentum spectra in decays of charged and neutral B mesons, and of the ratio of semileptonic branching fractions ${\cal B}\xspace(\B^+ \to X e \nu)$ and ${\cal B}\xspace(\B^0 \to X e \nu)$. These were performed on a sample of 231 million $B\kern 0.18em\bar{\kern -0.18em B}{}\xspace$ events recorded with the \mbox{\slshape B\kern-0.1em{\smaller A}\kern-0.1em B\kern-0.1em{\smaller A\kern-0.2em R}} detector at the $\Upsilon{(4S)}\xspace$ resonance. Events are selected by fully reconstructing a hadronic decay of one $B$ meson and identifying an electron among the decay products of the recoiling $\Bbar$ meson. We obtain ${\cal B}\xspace(\Bu \to X e \nu)$/${\cal B}\xspace(\Bz \to X e \nu)$ = $1.084 \pm 0.041_{\mathrm{(stat)}}\xspace\pm 0.025_{\mathrm{(syst)}}\xspace$.