Forward hadronic calorimetes are used in HI experiments to determine centrality and reaction plane. To understand the response and calculate systematic uncertanties a large amount of simulated data has to be produced. However a GEANT4 simulation of hadronic calorimeters may take as much time as of the whole detector if the calorimeter was hitted by a large fraction of nucleon spectators due to origination of many hadronic showers.
I would like to present the solution which was developed for the NA61/SHINE experiment at SPS CERN. It is a stand alone application based of fitted single nucleon responses, which allows practically instantaneous generation of a calorimeter responce even for Pb+Pb collisions.
SHINE is a fixed target experiment at SPS CERN. It has a hadronic calorimeter (PSD) which also plays a role of a beam dump. This detector has a very similar structure as the MPD's FHCal.