A study of $B^{0} \to \pi^{+} \pi^{-}$ decays using the BaBar detector

This thesis reports on the sensitivity of the BaBar detector to the study of CP violation in the B system. Due to the presence of $\pi^{0}$'s in most channels of interest to CP violation studies, an electromagnetic calorimeter with high efficiency and good energy resolution for low energy photons is needed for good $\pi^{0}$ and thus B mass resolution. A beam test of a prototype CsI electromagnetic calorimeter and its response to low energy electrons and pions is presented.