Kinematic Fitting of Two Photon Decays
From GlueXWiki
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.