Date and Author

GFLASH -

Parameterised simulation of electromagnetic shower in Geant4.7.0

Joanna Weng

Geant4 Technical Forum,

CERN, 16 November 2004

J. Weng, Geant 4 Technical Forum, 16 November 2004

J. Weng, Geant4 Workshop Catania, 4-9 October 2004

J. Weng, Geant 4 Technical Forum, 16 November 2004

Why GFLASH ?

Geant4 simulation of 50 GeV

shower in CMS ECAL

super module (PbWO4 crystals)

CMS detector

Problem:

Full simulation of LHC events is very time consuming (O (minutes/event)).

Much CPU time is spend in simulating electromagnetic shower

Aim: Speed up full simulation (OSCAR) in electromagnetic calorimeter (ECAL)

A Solution: GFLASH package (used in H1):

substitutes full tracking of high energy electrons/positrons in electromagnetic shower inside the ECAL with parametrized shower profile ->significant gain in speed, not much sacrifice in precision

,,;;;'

J. Weng, Geant4 Workshop Catania, 4-9 October 2004

Longitudinal Profile

Spatial energy distribution of electromagnetic showers is

given by three probability density functions:

(hep-ex/0001020, Grindhammer & Peters)

Longitudinal profile parameterised by gamma function with parameters  and :

In f the energy is assumed to be distributed uniformly:

J. Weng, Geant 4 Technical Forum, 16 November 2004

J. Weng, Geant4 Workshop Catania, 4-9 October 2004

Radial Profile

The average radial energy profile can be described by

(with 0 ≤ p ≤ 1) :

RC (RT ) is the median of the core (tail) component

RC (RT ) depends on the shower depth

r := Transverse size of shower, measured in Moliere radius (RM)

J. Weng, Geant 4 Technical Forum, 16 November 2004

GFlashShowerModel

J. Weng, Geant 4 Technical Forum, 16 November 2004

GFlashParticleBounds

GFlashHomoShower

parameterisation

Help stuff ...

GFLASH in Geant4

What will be available in Geant4.7.0?

(documented:) GFLASH library for homogeneous calorimeter

& simple example how to use it

Main concept:

Uses the Fast Shower Framework of Geant4

Every time a particle enters envelope (G4LogicalVolume, e.g. calorimeter), trigger is called

If certain criteria (energy bounds, particle type[@ moment: e-/e+], containment in volume) fulfilled, particle is killed and hits distributed according to calculated shower profile

How to use GFLASH

Example of Use:

In Detector Construction:

Assign GFLASH parameterisation to Envelope

theFastShowerModel = new GflashShowerModel("GflashShowerModel",

calo_log);

theParameterisation = new GflashHomoShowerParamterisation

(matManager->getMaterial(mat));

theFastShowerModel->SetParameterisation(*theParameterisation);

theFastShowerModel->SetParticleBounds(*theParticleBounds);

theFastShowerModel->SetHitMaker(*theHMaker);

In Physics List: Add FastSimulationManagerProcess

G4FastSimulationManagerProcess* theFastSimulationManagerProcess

= new G4FastSimulationManagerProcess();

{

(Loop over particles and add to Process Manager)

}

J. Weng, Geant 4 Technical Forum, 16 November 2004

Simple PbWO4 Cube

CPU time of full Geant 4.6.2 simulation and GFLASH shower parameterisation for a single electron (Pentium III @ 1Ghz) in an PbWO4 cube:

J. Weng, Geant 4 Technical Forum, 16 November 2004

Results quite promising :-);

Tggggitleds,sdf,gsdf;gls'd;fgl;'daslfg'sd

Simple PbWO4 Cube (2)

Only problem: GFLASH parameters obtained from Geant3.

-> For G(4)FLASH retuning can be necessary (radial profile).

For experiment specific geometries retuning often necessary

anyway, therefore it is possible to pass user-tuned parameters:

Geant 4.6.2 / Geant3 / GFLASH

Geant 4.6.2 / Geant3 / GFLASH

20 GeV e-

20 GeV e-

J. Weng, Geant 4 Technical Forum, 16 November 2004

GFlashHomoShowerParamterisation(G4Material * aMat,

GVFlashHomoShowerTuning * aPar)

Tggggitleds,sdf,gsdf;gls'd;fgl;'daslfg'sd

OSCAR Simulation

Visualization of CMS ECAL with OSCAR / IGUANACMS

(http://cmsdoc.cern.ch/oscar, http://iguanacms.web.cern.ch/iguanacms)

J. Weng, Geant 4 Technical Forum, 16 November 2004

Tggggitleds,sdf,gsdf;gls'd;fgl;'daslfg'sd

CMS ECAL simulation

J. Weng, Geant 4 Technical Forum, 16 November 2004

CPU time of full Geant 4.6.2 simulation and GFLASH shower parameterization for a single electron (Pentium III @ 1Ghz) inCMS ECAL simulation(OSCAR):

Tggggitleds,sdf,gsdf;gls'd;fgl;'daslfg'sd

Further plans

Design iteration to extend for sampling calorimeter

(together with ATLAS group[E.Barberio] )

Setup of (partial) tuning infrastructure:

tuning means refit of (energy dependent) parameters in the shown equations

for radial and longitudinal profile (details in hep-ex/0001020 )

-> especially for radial profile not trivial :-(

Improved handling of sensitive detectors:

At the moment one should be careful with

ProcessHits(G4Step *aStep, G4TouchableHistory * )

(mandatory method invoked when step is composed in sensitive

detector): Infos available with full tracking not available in fast

parametrization e.g. track information (since there is no track...)

Possible solutions : Flag to check if parametrization active ...

-> Discussion about other solutions in progress

J. Weng, Geant 4 Technical Forum, 16 November 2004

Conclusions

(First) GFLASH implementation will be available in Geant4.7.0

Is easy to use and provides the possibility to significantly speed up(electromagnetic) shower simulation

For complicated geometries or if more precision necessary,

GFLASH parameters should be tuned by the user

(tuning tools development in progress)

You are invited to try a GFLASH

``	“Fast Shower” and give us Feedback!

J. Weng, Geant 4 Technical Forum, 16 November 2004

2004-11-16T02:39:38