Neutral Decay of theωMeson

The reaction ${\pi }^{-}+p\to \omega +n$ at 1.2 $\frac{\mathrm{BeV}}{c}$ was detected by counter techniques. Recoil neutrons were detected in a scintillation counter array at ${\theta }_n={20}^{\circ }\pm 2^{\circ }$, and their velocity determined by a time-of-flight measurement. Measurement of the neutron direction and velocity determined the $\omega$ mass with resolution ±15 MeV, and enabled separation of $\omega$ production from background. Scintillation counters surrounding the hydrogen target distinguished charged from neutral $\omega$ decays, yielding a branching ratio: $\frac{{\Gamma }_{\mathrm{neutral}}}{{\Gamma }_{\mathrm{charged}}}=0.124\mathrm{}\pm 0.021$. Neutral $\omega$ decays were directly observed by conversion of the resulting $\gamma$ rays in a leadplate spark-chamber array. Events with three observed $\gamma$'s were fitted to the decay $\omega \to {\pi }^0+\gamma \to 3\gamma$ (a two-constraint fit). Twenty-six fits with ${\chi }^2<5\mathrm{}$ were found, of which five are estimated to be background. If $\omega \to {\pi }^0+\gamma$ is the only neutral mode, then we expect 29 observed ${\pi }^0\gamma$ decays, as calculated from the recoil-neutron measurements and spark-chamber efficiency. Thus our data give clear evidence that the mode $\omega \to {\pi }^0+\gamma$ represents a substantial fraction (consistent with 100%) of the $\omega$ neutral decays.