Electromagnetic shower reconstruction with emulsion films in the OPERA experiment

OPERA is a neutrino oscillation experiment designed to perform a ντ appearance search in the CNGS beam from CERN to Gran Sasso underground laboratory, 730 km from CERN. The identification of the τ lepton produced by a ντCC interaction is based on the use the Emulsion Cloud Chamber (ECC) which consists of a modular structure made of a sandwich of passive material plates interleaved with emulsion films. In addition of its very good tracking information capability, used to the detection of short-lived particles, the ECC can be used as a fine sampling electromagnetic calorimeter allowing the study of the τ→ e decay and the νμ → νe oscillation channel. We will report the method developed to reconstruct the electromagnetic showers with ECC and the energy measurement in the 1-10 GeV range.