A study of the transverse fluctuations of hadronic showers in the NOMAD electromagnetic calorimeter

The transverse shower shape of the energy deposition of hadrons in the NOMAD lead glass calorimeter has been studied by exposing a prototype of this calorimeter to pion test beams of various momenta and incident angles. Large event-to-event fluctuations in the shower shape and significant energy depositions far from the incident hadron were observed making it difficult to associate all the deposited energy to the incident hadron that caused it. Since in the NOMAD detector the momenta of charged hadrons are measured by a magnetic spectrometer, such an association is necessary to be able to subtract from the calorimeter ail the energy caused by the observed charged hadrons in order to avoid double counting. Probability functions based on the measurements have been developed to describe fluctuations of the lateral shower shape. Starting from these Functions, an algorithm is developed for identifying the energy deposition associated to a charged hadron. The identification and separation of overlapping showers based on these functions is also discussed. The Monte Carlo simulation of the calorimeter reproduces the test beam data well therefore allowing the application of the algorithm at angles and momenta not studied in the test beam. (C) 1998 Elsevier Science B.V. All rights reserved.