The Virtual MonteCarlo

1
The Virtual MonteCarlo

• D.Adamova2, V.Berejnoi1, R.Brun1, F.Carminati1,
  A.Fassó1, E.Futo1, I.Gonzalez3, I.Hrivnacova4,
  A.Morsch1
• 1CERN, Geneva 2NPI, Rez 3IFCA, Cantabria 4IPN,
  Orsay
• For the ALICE Collaboration
• Presented by I. Hrivnacova
• Conference forComputing in High Energy and
  Nuclear Physics
• La Jolla, 27 March 2003

2
Outline

• Interfaces
• Available MCs
• Examples
• Distribution
• Future

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The VMC Concept

• The Virtual MonteCarlo (VMC) has been developed
  in order to
• Run the same user application with all supported
  transport Monte Carlos
• Run different transport Monte Carlo programs
  without changing the user code and therefore the
  geometry definition, the detector response
  simulation, or input and output formats
• VMC decouples the dependence of a user code from
  a concrete MC

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VMC Concept
User Code
VMC
Geant3
Input
Geant4
Particles Hits
Geant3 VMC
Fluka
Geant4 VMC
Output
Fluka VMC
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Virtual Monte Carlo
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Interfaces (1)
Virtual MC

• TVirtualMC
• Interface to the Monte Carlo program
• Generalization of Geant3 functions for definition
  of simulation task
• Provides methods for definition of geometry and
  physics setup for access to tracked particle
  properties during stepping for run control
• Implementations
• TGeant3, TGeant4, TFluka (coming
  soon)
• Are provided for the user

Methods For Building Accessing Geometry
Methods For Building Accessing Materials
Methods For Setting Physics
Methods For Accessing Tracked Particle During
Stepping
Methods For Run Control
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Interfaces (2)
Virtual MC Application

• TVirtualMCApplication
• Interface to a user application
• Defines user actions at each stage of a
  simulation run
• Mandatory
• Implementation has to be done by a user

ConstructGeometry InitGeometry GeneratePrimaries
BeginEvent BeginPrimary PreTrack Stepping PostTrac
k FinishPrimary FinishEvent
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Interfaces (3)

• TVirtualMCStack
• Interface to a user defined particles stack
• Mandatory
• User can use the concrete stack classes provided
  in the examples or implement their own stack
  class
• TVirtualMCDecayer
• Interface to an external decayer
• Eg. Pythia6
• Optional

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Use of VMCGeometry Construction
void MyMCApplicationConstruct Geometry()
Double_t trackerTube3 trackerTube0 0.
trackerTube1 60. trackerTube2 50.
gMC-gtGsvolu("TRTU", "TUBE", fImedAl,
trackerTube, 3) Double_t posX -100.
Double_t posY 0. Double_t posZ 0.
gMC-gtGspos("TRTU", 1 , "EXPH", posX, posY, posZ,
0, "ONLY")
User MC Application
ConstructGeometry InitGeometry GeneratePrimaries
BeginEvent BeginPrimary PreTrack Stepping PostTrac
k FinishPrimary FinishEvent

• Geometry is defined by calls to TVirtualMC
  interface

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Use of VMCPrimary Particles
void MyMCApplicationGeneratePrimaries()
// Define particle properties // PDG
encoding // position vx, vy, vz, vt //
momentum px py, pz, e // // Add particle
to MC stack gMC-gtGetStack()
-gtSetTrack(toBeDone, -1, pdg, px, py, pz, e,
vx, vy, vz, t, )
User MC Application
ConstructGeometry InitGeometry GeneratePrimaries
BeginEvent BeginPrimary PreTrack Stepping PostTrac
k FinishPrimary FinishEvent

• Primary particles are defined by calls to the
  TVirtualMCStack interface

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Use of VMCHits Production
void MyMCApplication Stepping() // Get
track position Double_t x, y, z
gMC-gtTrackPosition(x, y, z) // Get energy
deposit Double_t edep gMC-gtEdep() //
Create user hit mySD-gtAddHit(x, y, z, edep)
User MC Application
ConstructGeometry InitGeometry GeneratePrimaries
BeginEvent BeginPrimary PreTrack Stepping PostTrac
k FinishPrimary FinishEvent

• The user stepping function is called by MC at
  each step
• User gets the properties of the tracked particle
  by calls to TVirtualMC and saves them in their
  own hits objects

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Available MCs

• Geant3, Geant4
• Geant3 VMC and Geant4 VMC in production
• Fluka
• Fluka VMC in development

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Available MCsGeant3 VMC

• Provided within a single package together with
  Geant321 (FORTRAN)
• Straightforward implementation
• VirtualMC was largely inspired by Geant3
• Geant3 Geometry Browser
• Provided within TGeant3
• http//alisoft.cern.ch/ people/morsch/Geant3GUI.ht
  ml

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Available MCsGeant4 VMC (1)

• Provided within a package - geant4_vmc
• Requires Geant4 installation
• Access to Geant4
• Switching between Root UI and Geant4 UI
• Geant4 classes are not processed by CINT G4
  objects are not accessible from the Root UI
• Use of G3toG4
• TVirtualMC has been inspired by Geant3
• An effort has been made to minimize the
  limitations of the G3toG4 tool in Geant4 4.0
• Support for reflections
• Limited support for MANY volume positions

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Available MCsGeant4 VMC (2)

• Geant4 VMC extensions
• Geant4 VMC Geometry Browser
• Analogy to Geant3 Geometry browser
• Geometry XML Convertor
• Enables to export Geant4 geometry to XML (AGDD)
  and then to browse and visualize using GraXML
• More on GraXML in the presentation
• GraXML Modular Geometric Modeller (J.
  Hrivnac)

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Available MCsFluka VMC

• In development by the ALICE collaboration and
  FLUKA team
• TFluka in AliRoot
• Implemented
• Functions for building/accessing geometry
• Use of Geant4 VMC Flugg
• Functions for accessing tracked particle during
  stepping
• Recording particles in VMC stack
• Functions for run management
• To be done
• Functions for setting physics
• External decayer

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Examples

• 3 examples provided in geant4_vmc
• In spite of being provided within Geant4 VMC,
  they are built independently and do not require
  Geant4 installation in case a user wants to run
  them with Geant3 only
• Geant4 novice examples N01, N02 and N03 rewritten
  with use of Virtual Monte Carlo
• Implement MC Application and MC Stack
• All examples are executed in the same way
• cd geant4_vmc/examples/E0n
• root
• root0 .x run_g3.C or run_g4.C

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• // Load basic libraries
• gROOT-gtLoadMacro(basiclibs.C)
• basiclibs()
• // Load this example library
• gSystem-gtLoad("libexample01")
• // MC application
• Ex01MCApplication appl
• new Ex01MCApplication("Example01", "The
  example01 MC application")

E01 run_g3.C run_g4.C
// Load Geant3 libraries gROOT-gtLoadMacro(g3libs
.C) g3libs()
// Load Geant4 libraries gROOT-gtLoadMacro(g4libs
.C) g4libs()
appl-gtInitMC("g3Config.C")
appl-gtInitMC("g4Config.C")
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E01 g3Config.C g4Config.C
void Config() new TGeant3("C Interface
to Geant3")
void Config()

// RunConfiguration for Geant4
TG4RunConfiguration runConfiguration new
TG4RunConfiguration() // Geant4 VMC
new TGeant4("TGeant4", "The Geant4 Monte Carlo",
runConfiguration)
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ExamplesAliRoot

• AliRoot Framework
• Integrates simulation, reconstruction and
  analysis software for the ALICE experiment
• Simulation based on Virtual Monte Carlo
• A complex example of VMC usage
• No MC specific code in user code
• PPR production with Geant3
• More on AliRoot in the presentations
• The AliRoot Framework, status and perspectives
  (F.Carminati)
• Simulation in ALICE (A. Morsch)
• ALICE experience with Geant4 (I. Gonzalez)

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AliRoot Geometry
Dimuon Arm
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AliRoot Hits Production
Geant3
Geant4
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VMC Future (1)

• Integration of the new Root geometrical modeller
  (TGeo) in VMC in progress
• Will then be able to define MC geometry directly
  via TGeo
• Geant3, Fluka
• Replacement of the native geometry with TGeo
  inside the program itself
• Geant3
• Already operational, close to completion
• Production release in coming weeks
• Fluka
• Work is ongoing

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VMC Future (2)

• Geant4
• Discussions about using the Root geometry
  modeller through an abstract interface to Geant4
  geometry have been started
• RootToG4 converter
• Converter from Root geometry to Geant4 native
  geometry
• Already operational, close to completion
• Production release will follow the release of the
  new Geant3 version
• More on TGeo in the presentation
• A Geometrical Modeller for HEP (A. Gheata)

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Distribution

• ROOT CVS server
• mc core package (interfaces), in Root
• geant3, geant4_vmc
• 2 independent modules (parallel to root)
• cvs -d pservercvs_at_root.cern.ch/user/cvs co P
  geant3
• cvs -d pservercvs_at_root.cern.ch/user/cvs co P
  geant4_vmc
• ROOT Web
• http//root.cern.ch/root/vmc/VirtualMC.html
• Distribution of sources
• geant321_vmc.version.tar.gz
• geant4_vmc.version.tar.gz

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Summary

• VMC allows the user to run different transport
  MonteCarlos from the same user code
• On the menu today Geant3, Geant4
• Coming soon Fluka
• VMC available from
• http//root.cern.ch/root/vmc/VirtualMC.html