A hadron shower library for FOCUS experiment

FOCUS is a charm photoproduction experiment at Fermilab. It is a large aperture spectrometer capable of detecting the particles produced in the interactions of the photon beam of about 170 GeV on a BeO target. It consists of: the silicon micro-strips layers for high resolution tracking and vertexing, five MWPC stations and two straw tube stations to trace the particles deflected by two large aperture magnets of opposite polarity, three Cherenkov counters for particle identification, two e.m. calorimeters to detect the photons and electrons, a hadron calorimeter to trigger on the total hadronic energy released in the interaction and two muon stations to detect the muons. The experiment has collected over 7 x 109 triggers of charm candidates. For data analysis, large samples of events have to be simulated. Tracking all the particles produced during the shower development in the calorimeters as done in GEANT is a very time consuming operation. In order to increase the computation speed, a Hadron Shower Library (HSL) will be used in FOCUS to replace the detailed shower simulation. The HSL is created by generating a sample of particle showers in GEANT and storing the information about primary particles and the calorimeter response in a random access file. GEANT was found to describe well the pion calibration data. The implementation of HSL for FOCUS is presented in detail. The performance in terms of computing speed and accuracy is evaluated. (authors)