Role of Meson-Meson Correlation Effects in the $\NNb\to\rho\pi$   Annihilation Process
  Meson-meson correlation effects are investigated in the $\NNb\to\rho\pi$ annihilation process using a realistic meson-exchange model for the $\rho\pi$ interaction determined previously, together with a conventional baryon-exchange transition model and a consistent $\NNb$ interaction. For $\NNb$ $S$-states, they have a drastic effect and bring the relative (${^1S_0}/{^3S_1}$) branching ratio up to the experimental value, thus resolving the long-standing so-called ``$\rho\pi$'' puzzle. For $\NNb$ $P$-states, their effect is of minor importance, and discrepancies remain for those ratios involving annihilation from the $\NNb({^3P_J})$ state to $\rho\pi(l'=2)$. 
V. Mull, G. Janssen, J. Speth, and K. Holinde