A Measurement of the B0 --> J/psi pi+pi- Branching Fraction

Abstract

We present a preliminary measurement of the branching fraction for the decay of the neutral $B$ meson into the final state J/$\psi {\pi }^{+}{\pi }^{-}$. The data set contains approximately 56 million $B\bar{B}$ pairs produced at the ${\rm Y}(4S)$ resonance and recorded by the BaBar detector at the PEP-II $e^{+}{e}^{-}$ collider. The result of this analysis is $\mathcal{B}(B^0\to J/\psi {\pi }^{+}{\pi }^{-}$) = (5.0 $\pm$ 0.7 $\pm$ 0.6)$\times 10^{-5}$, where the first error is statistical and the second is systematic.

16 pages, 1 postscript figure, presented at the XXXVIIth Rencontres de Moriond on QCD and Hadronic Interactions