Meson production on complex nuclei by pi^- with the Crystal Ball   detector
  We report on preliminary results for the production of neutral mesons by 750 MeV/$c$ $\pi^-$ on complex nuclear targets (C, Al, Cu) and hydrogen. Our simultaneous measurement of $\pi^0$, $2\pi^0$, and $\eta$ final states allows an investigation of the nuclear final-state-interaction effects. The data show that nuclear absorption is mainly responsible for an observed change in the shape of the $2\pi^0$ invariant mass spectra. Our preliminary result for the $\sigma \to \gamma \gamma$ branching ratio is BR$(\sigma \to \gamma \gamma) < 3.6\times 10^{-3} \times \phi$ at 90% C.L. on a carbon target, where $\phi$ is the fraction of $2\pi^0$ produced via the $\sigma$ intermediate state. 
A.Starostin, B.M.K.Nefkens, H.M.Staudenmaier (for the Crystal Ball   Collaboration)