1) directory photons is a plugin to analyze events where photons were
   genenrated from the target.
   the output file is a root file called photonhists.root
2) pandf.cc  analyzes the file photonshists.root and creates a new
   root file called hists.root
3) the directory src contains a scaner program to scan through
   the file hists.root but expectes the file to be renamed first
   to something like hists_TargetCenter.root, hists_TargetCenterplus10cm.root
   or hists_TargetCenterminus10cm.root