  We report on the simulation results for the angular resolution of an
electromagnetic (EM) sampling calorimeter with photons in the range of 100~MeV
to 2~GeV. The simulation model of the EM calorimeter consists of alternating
layers of a 1-mm-thick lead plate and a 5-mm-thick plastic scintillator plate.
The scintillator plates are alternately segmented into horizontal and vertical
strips. In this study, we obtain energy deposits in individual strips using
Geant4 simulations and reconstruct the incident photon angles using XGBoost
with gradient-boosted decision trees. The performance of the angle
reconstruction depends on the detector configuration and the accuracy of
machine learning. The angular resolution is well described by the expression
$0.24^{\circ} \oplus 1.25^{\circ}/\sqrt{E_{\gamma}}$, where $E_{\gamma}$ is the
incident photon energy in GeV, for strips of 15 mm and 32 layers. This energy
dependence is consistent for different incident angles in the range of
10$^{\circ}$ to 40$^{\circ}$.

Instrumentation and Detectors