GFLASH Simulation at CMS

The computing time needed for the simulation of high energy electromagnetic showers can become very large, since it increases approximately linearly with the energy absorbed in the detector. Using parameterizations instead of individual particle tracking for electromagnetic showers can speed up the simulations considerably without sacrificing much precision. The GFLASH package allows the parameterization of electron and positron showers in homogeneous calorimeters. One of the primary goals of GFLASH simulation is to tune the measured deposited energy in data due to detector effects and physics processes within the calorimeter system.

GFLASH gives good results inside the GEANT4 fast shower framework when compared with the full electromagnetic shower simulation. For the longitudinal profiles the difference between full simulation and GFLASH parameterization is at the level of a few percent. Because the radial profiles are slightly broader, the differences may reach larger than 10%. The gain in speed, on the other hand, is impressive. The simulation of a 1 TeV electron in a PbWO4 cube is 160 times faster with GFLASH as an example.