Performance of the PrimEx Electromagnetic Calorimeter

We report the design and performance of the hybrid electromagnetic calorimeter consisting of 1152 $PbWO_4$ crystals and 576 lead glass blocks for the PrimEx experiment at the Jefferson Laboratory. The detector was built for high precision measurement of the neutral pion lifetime via the Primakoff effect. Calorimeter installation and commissioning was completed with the first physics run in fall of 2004. We present the energy and position resolution of the calorimeter. Obtained $\pi^0$ mass resolution of $1.3 \mathrm{MeV/c^2}$ and its production angle resolution of $0.34 \mathrm{mrad}$ demonstrate the ability of the experiment to extract the $\pi^0$ lifetime on one percent level.