Background Subtraction

A small quantity of two-photon background events from $\pi ^o$ decays and from multi-$\pi$ stops that survive the applied cuts, were subtracted from the candidate signal events. In the final set of 635 signal $\pi ^-p\rightarrow \gamma \gamma n$ event candidates, events above 150 MeV were mostly contributions from random multi-$\pi$ accidentals. The contribution from $\pi ^o$-tail events were also determined and subtracted. The procedures developed and applied for the background subtraction are described in the following sections.