A Model Independent Measurement of the Branching Fraction of $\Upsilon(4S)$ Decays to Neutral $B$ Pairs

Isospin violation in $\Upsilon(4S) \to B\bar{B}$ decays induces a difference in the branching fractions $f_{00} = {\cal B} (\Upsilon(4S) \to B^0 \bar{B}^{0})$, and $f_{+-} = {\cal B} (\Upsilon(4S) \to B^+B^-)$. These branching fractions are important inputs for many $B$ meson measurements at $B$ factories. Isospin violation in the $\Upsilon (4S)$ resonance decays may be at the level of a few percent mostly due to electromagnetic interactions and the mass difference between the up and the down quarks. We discuss a model independent measurement of the $f_{00}$ branching fraction based on a data sample of $\sim$470 million $B \bar{B}$ pairs collected at the $\Upsilon(4S)$ resonance with the {\sl B{\scriptsize A}B{\scriptsize AR}} detector. We reconstruct neutral $B$ meson in the channel $\bar {B}^0 \to D^{*+} \ell^{-} \bar{\nu}_{\ell}$ using a partial reconstruction technique.