Kinematic Fitting of Two Photon Decays

Procedure

• generate 1 GeV η's which decay generically in the GlueX detector
• reconstruct η→γγ and π⁰→γγ
  • π⁰ produced in η decay have low momentum
  • very few additional "clean-up" cuts applied
• kinematically fit η's and π⁰'s and examine confidence level distributions and pull distributions.
  • tests the accuracy of the photon covariance matrix

Results

The plots below show confidence level and two photon invariant mass for four types of fits:

• π⁰ fit with two photons in the FCAL
• π⁰ fit with two photons in the BCAL
• η fit with two photons in the FCAL
• η fit with two photons in the BCAL

Combinatoric backgrounds produce a peak at low confidence level and tails away from the nominal two-photon invariant mass. The relatively flat confidence level distribution is an indication that photon covariance matrices are properly constructed.