  The studies presented in this paper provide a first experimental test of the
Particle Flow Algorithm (PFA) concept using data recorded in high granularity
calorimeters. Pairs of overlaid pion showers from CALICE 2007 test beam data
are reconstructed by the PandoraPFA program developed to implement PFA for a
future lepton collider. Recovery of a neutral hadron's energy in the vicinity
of a charged hadron is studied. The impact of the two overlapping hadron
showers on energy resolution is investigated. The dependence of the confusion
error on the distance between a 10 GeV neutral hadron and a charged pion is
derived for pion energies of 10 and 30 GeV which are representative of a 100
GeV jet. The comparison of these test beam data results with Monte Carlo
simulation is done for various hadron shower models within the GEANT4
framework. The results for simulated particles and for beam data are in good
agreement thereby providing support for previous simulation studies of the
power of Particle Flow Calorimetry at a future lepton collider.
