This example demonstrates how to use G4FastSimHitMaker helper class to create multiple energy deposits from the fast simulation model.

It requires sensitive detector class to inherit from both base classes:

G4VSensitiveDetector: for processing of detailed/non-fast simulation hits
G4VFastSimSensitiveDetector: for processing of fast sim (G4FastSim) hits Hits are placed in the same hit collection, so they can be used to compare between the full and the fast simulation.

The geometry used in the example is a homogeneous cylinder of lead, with 3D readout geometry (cylindrical). Analysis of energy deposits is done in the event action.

Detector description

The detector is a homogeneous cylinder of lead. It is segmented along z, R and phi to create a readout geometry in the cylindrical coordinates.

Fast simulation is attached to the region of the detector.

Sensitive detector

Sensitive detector inherits from both base classes:

G4VSensitiveDetector: for processing of detailed/non-fast simulation hits
G4VFastSimSensitiveDetector: for processing of fast sim (G4FastSim) hits. Hits are placed in the same hit collection, with a different flag to distinguish between those originated in the full simulation, and those from the fast simulation. During visualisation, hits are represented as volumes of different colour: green for full simulation and red for fast simulation.

Primary generation

Particle gun is used as a primary generator. The direction of particles is along the axis of symmetry of the detector (cylinder). It is positioned 10 cm in front of the entrance to the detector. 10 GeV electron is used by default. Those values can be changed using /gun/ UI commands.

Physics List

FTFP_BERT modular physics list is used. On top of it, fast simulation physics is registered for selected particles (electrons, positrons, and photons).

User actions

Par03RunAction : run action used for initialization and termination of the run. Histograms for analysis of shower development in the detector are created.
Par03EventAction : event action used for initialization and termination of the event. Analysis of shower development is performed on event-by-event basis.

Output

The execution of the program (examplePar03) produces an output with histograms.

The macro file examplePar03.in specifies three runs. Each run is made of 100 events, for single 10 GeV electron beams. The first run is executed with fast simulation model activated with defualt parameters. The second run executes fast simulation with modified parameters. For the third run the fast simulation model is disactivated. Three output files are produced: two with shower development from the fast simulation (with different parameters), and from the full simulation.

How to build and run the example

Compile and link to generate the executable (in your CMAKE build directory):
```
% cmake <PAR03_SOURCE>
% make
```
Execute the application (in batch mode):
```
% ./examplePar03 -m examplePar03.in
```
which produces three root files: Par03_fastsim_100events.root, Par03_fastsimModified_100events.root, and Par03_fullsim_100events.root.
Execute the application (in interactive mode):
```
% ./examplePar03
```
which allows to visualize hits.

UI commands

UI commands useful in this example:

activation/disactivation of the fast simulation model:

/param/ActivateModel model
/param/InActivateModel model

particle gun commands

/gun/particle e+
/gun/energy 50 GeV
/gun/direction 0 0.2 1
/gun/position 0 0 0

UI commands defined in this example:

detector settings

/Par03/detector/print
/Par03/detector/setDetectorRadius 10 cm
/Par03/detector/setDetectorLength 30 cm
/Par03/detector/setDetectorMaterial G4_Pb
/Par03/detector/setNbOfLayers 100
/Par03/detector/setNbOfPhiCells 20
/Par03/detector/setNbOfRhoCells 100

fast simulation settings

/Par03/fastSim/print
/Par03/fastSim/transverseProfile/sigma 20 mm
/Par03/fastSim/longitudinalProfile/beta 0.6
/Par03/fastSim/longitudinalProfile/alpha 2.
/Par03/fastSim/longitudinalProfile/maxDepth 20
/Par03/fastSim/numberOfHits 500