Reconstruction of the π deg. kinematics from γγ decay

In this paper we discuss the quality of the π deg. kinematics reconstructed from the measurement of both decay photons in electromagnetic segmented calorimeter. The standard method of photon energy scaling is compared to the kinematically constrained fit procedure. The χ2 value from a fit to a given event was a subject of quantitative confidence level analysis. We demonstrate that the kinematical fit procedure has the following advantages compared to the energy-scaling method: (i) the width of the reconstructed pion energy distribution becomes narrower by 14%, and (ii) the efficiency of π deg. selection for the reconstruction purposes is much higher at the same confidence level. After applying the kinematical fit method to the experimental data, the reconstructed pion energy spectrum does not violate the kinematical limit imposed by the energy conservation, in contrast to the energy-scaling method