Extracting longitudinal shower development information from crystal calorimetry plus tracking

We present an approach to derive longitudinal shower development information from the longitudinally unsegmented BABAR electromagnetic calorimeter by using tracking information. Our algorithm takes advantage of the good three-dimensional tracking resolution of BABAR, which provides an independent geometric constraint on the shower as measured in the BABAR crystal calorimeter. We show that adding the derived longitudinal shower development information to standard particle identification algorithms significantly improves the low momentum separation of pions from electrons and muons. We also verify that the energy dependence of the electromagnetic shower development we measure is consistent with the prediction of a standard electromagnetic shower model.