  In the ILD detector, HCAL is inside the coil. The HCAL is about 5 interaction
length thick, and ECAL is about 1 interaction length thick. For example, an
eighty GeV hadron, it is only 95% energy will be contained in ECAL plus HCAL.
We need a topological reconstruction of the leakage. This has been studied with
experimental data collected using the CALICE prototypes, during the 2007 test
beam campaign at CERN. The complete setup of the experiment consisted of a
silicon-tungsten electromagnetic calorimeter, an analog scintillator-steel
hadron calorimeter and a scintillator-steel tail catcher. Events collected
using pion beams in the energy range 8-100 GeV are selected and compared to the
Monte Carlo simulations. While the leakage from the full setup is negligible,
when removing the tail catcher information either partly or completely the
energy loss becomes significant and affects the performance. The average
measured energy decreases below the expected beam energy and the resolution
deteriorates. A correction to the leakage was implemented for pions. The
results obtained show that the correction is powerful in restoring the mean
value of the measured energy distributions back to the expected beam energy,
with an accuracy at the 1-2% level over the whole energy range. The relative
improvement on the resolution is about 25% at 80 GeV, decreasing at lower
energies together with the impact of the leakage.
