Measurement of the Branching Fraction of Upsilon(4S) --> B0B0bar

TL;DR

This paper presents the first measurement of the branching fraction of Upsilon(4S) decaying into B0B0bar pairs, using partial reconstruction techniques with data from the BABAR detector, achieving high precision and independence from certain decay assumptions.

Contribution

It introduces a novel measurement of the Upsilon(4S) to B0B0bar branching fraction using partial reconstruction, independent of specific decay branching fractions and isospin assumptions.

Findings

Measured f00 = 0.487  0.010 (stat)  0.008 (sys)

First measurement of this branching fraction

Result is independent of certain decay parameters

Abstract

We report the first measurement of the branching fraction f00 for Upsilon(4S) --> B0B0bar. The data sample consists 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} in which only the charged lepton and the soft pion from the decay D^{*+} --> D0 pi^+ are reconstructed, we obtain f00 = 0.487 \pm 0.010(stat) \pm 0.008(sys). Our result does not depend on the branching fractions of B0bar --> D^{*+} \ell^{-} \bar{\nu}_{\ell} and D^{*+} --> D0 pi^+ decays, on the ratio of the charged and neutral B meson lifetimes, nor on the assumption of isospin symmetry.