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

Abstract

We present a 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 with the BaBar detector at the PEP-II asymmetric-energy $e^{+}{e}^{-}$ storage ring. The result of this analysis is $\mathcal{B}$($B^0\to J/\psi {\pi }^{+}{\pi }^{-}$) = (4.6 $\pm$ 0.7 $\pm$ 0.6)$\times 10^{-5}$, where the first error is statistical and the second is systematic. In addition we measure $\mathcal{B}(B^0\to J/\psi {\rho }^0)=(1.6\pm 0.6\pm 0.4)\times 10^{-5}$.

7 pages, 2 postscript figues