Meson production on complex nuclei by pi^- with the Crystal Ball detector

Abstract

We report on preliminary results for the production of neutral mesons by 750 MeV/$c$ $π^-$ on complex nuclear targets (C, Al, Cu) and hydrogen. Our simultaneous measurement of $π^0$, $2π^0$, and $η$ 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 $2π^0$ invariant mass spectra. Our preliminary result for the $σ\to γγ$ branching ratio is BR$(σ\to γγ) < 3.6\times 10^{-3} \times ϕ$ at 90% C.L. on a carbon target, where $ϕ$ is the fraction of $2π^0$ produced via the $σ$ intermediate state.