A photon is reconstructed
from the pair of 
tracks found from the hits
in the drift chamber cells. Hits in the cells were fitted to a circle
to find a single charged track, and two
such tracks with opposite curvature that originate from within a certain
distance at the target were accepted as a photon candidate.
At the initial stages of analysis, events that have at least two
such photons were selected as a
event candidate.
The reconstruction of two-photon events involved requiring the
events to pass:
of the fitted tracks,
and a minimum number of points in the track fitting.
trajectories at the lead converter and photon trajectories at the
target. At least 4 such good tracks were required. Further, as part of the
photon cut, another 
sector cut was applied that concerned the
tracks that fire a counter.
These pair of tracks that constitute a photon candidate were
required to intersect the counter that fired. Two such photons were also
required to arrive within 
20 ns of each other.
|
, N
, etc. are given in Section 
Tracking Cut
track (wrap)
points
track (wrap)
points
