Measurement of the Branching Fraction of e^+e^- --> B0B0bar at the Upsilon(4S) Resonance

TL;DR

This paper presents a precise measurement of the B0B0bar production fraction at the Upsilon(4S) resonance, crucial for B physics studies, using partial reconstruction techniques with the BABAR detector.

Contribution

It provides a new, model-independent measurement of the B0B0bar branching fraction at the Upsilon(4S), reducing dependence on decay branching ratios and isospin assumptions.

Findings

Measured f00 = 0.486 ± 0.010 (stat) ± 0.009 (sys)

Result is independent of B and D* decay branching fractions

Contributes to understanding isospin violation in B meson production

Abstract

We report a measurement of the branching fraction e^+e^- --> B0B0bar with a data sample of 81.7 fb^-1 collected at the Upsilon(4S) resonance with the BABAR detector at the PEP-II asymmetric-energy e^+e^- storage ring. Using partial reconstruction of the decay B0bar --> D^{*+} \ell^{-} \bar{\nu}_{\ell} we obtain a preliminary result of f00 = 0.486 +- 0.010(stat.) +- 0.009(sys.). Our result does not depend on branching fractions of the B0bar and the D^{*+} decay chains, on the simulated reconstruction efficiency, on the ratio of the charged and neutral B meson lifetimes, nor on assumption of isospin symmetry. This measurement is important for normalizing many B decay branching fractions, and contributes to our understanding of isospin violation in the Upsilon(4S) system.