Neutral decay modes of the η0 meson

The branching ratios of the decay of the η0 meson into neutral products have been measured. The η0 is produced in the reaction π-p→η0+n, and the decay products are observed as γ rays by a system of optical spark chambers and counters in nearly 4π geometry. Emphasis was placed on examining evidence for the decay mode η0→π0γγ (→4γ). Measurement of the neutron time of flight in the production process, together with detailed measurement and kinematical analysis of the pictures showing four γ rays, enables us to test each event for consistency with such a decay mode, and also for the "background" process π-+p→2π0+n. From what is essentially a comparison of the observed rates for these processes, we obtain the upper limit for (η0→π0γγ)(η0→all neutrals) ≤7% (90% confidence level), a result which is relatively insensitive to estimates of the efficiency of the detecting system. We also obtain (η0→3π0)(η0→2γ)=0.75±0.09.