A method has been proposed which employs a statistical technique to exploit the photon tagger and forward scintillator information in the Radphi data sample. The method enables the extraction of spectra corresponding to all-neutral triggers in true association with tagged photons in the presence of an arbitrary background from accidental coincidences, at the cost of some statistical precision. The method has been tested by selecting a sample of fully-contained forward events and comparing the total energy of reconstructed showers in the forward calorimeter with the energy of the incident photon as given by the tagger. Excellent agreement has been observed between expected and measured forward energy, once one takes into account the typical 100 MeV that is transfered to the recoil proton. A tail on the low-energy side of the total energy spectrum is attributed primarily to the spread in the energy of the recoil proton (and nucleus).
Examination of the cuts used to select a sample of fully-contained forward events reveal the importance and power of the barrel gamma veto to remove events with significant neutral energy outside the forward calorimeter. In fact, without the barrel gamma veto the peak in the total forward energy spectrum at the tagged energy was completely washed out. Without the bgd information, reconstructing a clean sample of exclusive neutral events in the forward calorimeter would have proved impossible with Radphi. On the other hand, the barrel gamma veto also imposes a steep cost of nearly an order of magnitude in terms of statistics. It is therefore highly desirable to find and perfect a method for recovering these events by reconstructing barrel photons.
The statistics of a clean sample of all-neutral tagged fully-contained forward events of a given multiplicity have been computed. Sample sizes of order a million are available up to multiplicity five. Software tools for applying the method presented have been checked into the Radphi cvs repository, and verified. Instructions for their use have been provided.