First Measurement of the Branching Fraction of e^+e^- --> B0B0bar

TL;DR

This paper presents the first direct measurement of the e^+e^- to B0B0bar production rate at the Upsilon(4S) resonance, using partial reconstruction techniques with data from the BABAR detector.

Contribution

It introduces a novel method for measuring the B0B0bar production fraction that does not rely on specific branching fractions or simulation-dependent efficiencies.

Findings

Measured B0B0bar production fraction: 0.486 ± 0.010 (stat) ± 0.009 (sys)

Method is independent of B0bar and D*+ decay branching fractions

First direct measurement of this production rate at Upsilon(4S)

Abstract

We report the first measurement of the absolute branching fraction e^+e^- --> B0B0bar at the Upsilon(4S) resonance using data collected with the BABAR detector at the PEP-II asymmetric-energy e^+e^- storage ring. The analysis is performed with partial reconstruction of the decay B0bar --> D^{*+}\ell^{-} \bar{\nu}_{\ell}$, where the presence of a signal decay is determined using only the lepton and the soft pion from the D^{*} decay. By reconstructing events with one or two signal decays we obtain a preliminary result of e^+e^- --> B0B0bar = 0.486 \pm 0.010(stat.) \pm 0.009(sys.)$. Our result does not depend on branching fractions of the B0bar and the D^{*+} decay chains, on the individual simulated reconstruction efficiencies, on the ratio of the charged and neutral B meson lifetimes, or on the assumption of isospin symmetry.