Speaker
Summary
The simulation of the ATLAS detector is largely dominated by the
showering of electromagnetic particles in the heavy parts of the
detector, especially the electromagnetic barrel and endcap
calorimeters, when full showering is simulated by GEANT4. The ATLAS
simulation includes a fast simulation option that achieves a
significant improvement in simulation speed. In this technique,
simulated showers from low-energy particles are "frozen" and stored in
a library, that is distributed with each software release. These showers
are then imported at runtime during physics simulation. The
shower libraries are built and stored in separate "bins" in order to
follow geometrical variations in calorimeter response. Simulation in
the presence of frozen showers is then required to develop the shower
down to ~ 1 GeV, at which point the shower is terminated by
substituting a frozen shower. The procedure can now be applied in all
of the electromagnetic compartments of the ATLAS calorimetry.
In this talk discuss mostly the frozen shower algorithms and their
performance, but we also include a discussion of alternate approaches
to fast shower simulation (e.g. Parameterization) that can have been
applied in ATLAS.
