Summary

In Figure 6.11, while the full curve (solid line) corresponds to Beder's predicted $\pi ^-p\rightarrow \gamma \gamma n$ branching ratio of 5.06 $\times$ 10$^{-5}$, our measured data points correspond to the branching ratio obtained from our experiment (3.05$\pm$0.41)$\times$ 10$^{-5}$. The plots in Figure 6.11 show that the $\pi ^-p\rightarrow \gamma \gamma n$ branching ratio and opening angle distributions from experiment and theory are in reasonable agreement. However, our measured branching ratio is somewhat smaller than the predicted theoretical branching ratio. Since Beder's calculation was performed at tree-level and neglects contributions from pion loops, etc, such higher-order terms might explain the difference between experiment and theory.