Conversion of Gamma Rays from the Decayη0→π++π−+γ

Abstract

A search for electron pairs produced in hydrogen by the gamma rays from a sample of 33 kinematically determined events ${\pi }^{+}p\to {\pi }^{+}\mathrm{pn}$, $\eta \to {\pi }^{+}{\pi }^{-}\gamma$ has yielded one event, where 0.4 events are expected. A search for six-pronged events in the same 72-in. bubble-chamber film yielded three events. One event is an example of the internal-conversion process $\eta \to {\pi }^{+}{\pi }^{-}{e}^{+}{e}^{-}$, and gives an internal-conversion probability $\frac{\Gamma (\eta \to {\pi }^{+}{\pi }^{-}{e}^{+}{e}^{-})}{\Gamma (\eta \to {\pi }^{+}{\pi }^{-}\gamma )}=0.026\mathrm{}$, based on one event. (The other two events arise from ordinary Dalitz decays of ${\pi }^0$.) No example was found of ${\pi }^{+}p\to {\pi }^{+}p{\pi }^{+}{\pi }^{-}{\pi }^{+}{\pi }^{-}$, although the c.m. energy is 120 MeV above threshold. One event would have corresponded to a cross section of 0.35 μb.