Performance of the PbWO$_4$ Hybrid Electromagnetic Calorimeter at Jefferson Laboratory

The goal of the PrimEx experiment at Jefferson Lab is to perform a high precision measurement of the $\pi^0$ lifetime via the Primakoff effect. The initial data-taking phase has recently been completed. A new electromagnetic hybrid calorimeter (HYCAL) consisting of 1152 lead tungstate (PbWO$_4$) crystals and 576 lead (Pb) glass Cherenkov modules was constructed by the collaboration to conduct the lifetime measurement with a precision of 1.5\%. This novel electromagnetic calorimeter has high resolution, acceptance, and efficiency; characteristics that are required for the detection of the $\pi^0$ decay photons. The HYCAL has been tested with photon beams in the few GeV energy range. Results for the energy and position resolutions for both PbWO$_4$ and Pb-glass, including the transitions regions, will be presented.\\ \\ This project is supported under NSF MRI grant PHY-0079840.