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The Virtual Monte-Carlo, status and applications. R.Brun (1) , F.Carminati (1) , A.Fasso (2) , E.Futo (1) , A.Gheata (1,3) , M.Gheata (3) , P.Hristov (1) , I.Hrivnacova (4) , A.Morsch (1) 1 – CERN, 2 – SLAC, 3 – ISS Bucharest, 4 – IPN Orsay Presented by: A.Gheata. Outline.

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the virtual monte carlo status and applications

The Virtual Monte-Carlo, status and applications

R.Brun(1), F.Carminati(1), A.Fasso(2), E.Futo(1), A.Gheata(1,3), M.Gheata(3), P.Hristov(1), I.Hrivnacova(4), A.Morsch(1)

1 – CERN, 2 – SLAC, 3 – ISS Bucharest, 4 – IPN Orsay

Presented by: A.Gheata

outline
Outline
  • Concept and current structure
  • Geometry and VMC
  • Status of the interfaces to specific MC’s
  • Validation tests

VMC-Status and Applications

a classical transport mc application

Application area

MC area

GENERATE

PUSH PRIMARIES

Application

stack

Generators

Particle stack

External decayer

PUSH SECONDARIES

DETECTOR & PHYSICS DESCRIPTION

POP

Geometry definition

Physics processes

Run configuration

Magnetic field

Cuts

User application

Run manager

Run loop

Event loop

INPUT

Physics models

Step interpreter

Stepping manager

State & tracking flags

Current volume, material, …

Track state: entering, exiting, alive, new, …

Physical process type

PROCESS SELECTION & PHYSICAL STEP

GEOMETRY CREATION

ADVERTISE STEP

Geometrical

modeller

Hits generation

Digitization

STEPING ACTIONS

NAVIGATION QUERIES/ANSWERS

OUTPUT

A classical transport MC application
  • Experiment/MC – tailored application

VMC-Status and Applications

vmc concept

User

Code

VMC

GEANT3

Input

GEANT4

Particles

Hits

GEANT3 VMC

FLUKA

GEANT4 VMC

Output

FLUKA VMC

VMC concept
  • Transport MC transparent to the user application (more details in the VMC presentation at CHEP03)

VMC-Status and Applications

benefits
Benefits
  • Running different transport MC’s from the same application
  • Using the same geometry description
    • Even the same geometry engine – TGeo (not yet the case for G4)
  • No need to customize detector response, physics configuration and cuts (partially) or input/output according the transport code

VMC-Status and Applications

geometry description and representation
Geometry description and representation
  • Geometry is a sensitive issue for transport codes

G3 geom.

VMC

GEANT3

transport

g2root

TGeant3

ROOT geom.

USER

CODE

Not yet

RootToG4

GEANT4

transport

TGeant4

g3tog4

G4 geom.

Flugg

G4toRoot

FLUKA

transport

TFluka

ROOT geom.

VMC-Status and Applications

structure of vmc

TVirtualMCApplication

TVirtualMC

TVirtualMCStack

TVirtualMCDecayer

UserStack

Pythia6

TGeant3

UserApplication

TGeant4

TFluka

Structure of VMC
  • Communication allowed only via virtual interface

VMC-Status and Applications

status
Status
  • Consolidation of old interfaces and further development of the new ones
  • Additions (mostly user demands):
    • Added new functions to enable a user to define ions and own particles
      • TVirtualMC::DefineIon(…)
      • TVirtualMC::DefineParticle(...)
      • TVirtualMCApplication::AddParticles()
    • Added function to enable a user to abort run
      • TVirtualMC::StopRun()
    • Consolidation of interfaces
      • more meaningful names in TVirtualMCStack functions
      • added Bool return value to TVirtualMC functions which could fail:
        • SetCut(), SetProcess(), DefineParticle(), DefineIon()
  • No other major changes in the user interface
    • Most efforts directed during last year to development of TFluka
    • Geometry converters RootToG4 and G4ToRoot (see "The Virtual Geometry Model“ by I.Hrivnacova)

VMC-Status and Applications

geant3 vmc
Geant3 VMC
  • In production in ALICE since quite a while
    • Implementation very stable : negligible changes since last year
  • Just few corrections compared to last year
    • Some fixes in the version TGeant3 + TGeo
  • Ongoing extensive tests for TGeo vs. G3 native geometry validation
    • Version using ROOT TGeo navigation planned to enter production next year

VMC-Status and Applications

validation of g3 with tgeo navigation

GEANT3 crossing

G3+TGeo corresponding crossing

v

dr

Boundary

Validation of G3 with TGeo navigation
  • Comparisons at hits level done in ALICE
    • No relevant differences found
      • See “A geometrical modeler for HEP”

presentation at CHEP03

    • More detailed analysis at detector module

level continuing

  • Ongoing step-by-step comparisons
    • Already done for simple geometries
    • Geantinos shot in partial ALICE geometry
      • Differences at the expected level
      • Fine tuning of TGeo behavior when

tracking close to boundaries

      • Analysis of possible rounding errors
      • Identify all possible remaining hidden

problems in the interface or in TGeo itself

  • Feed-back from other people that already

started this kind of comparisons is welcome !

VMC-Status and Applications

geant4 vmc
Geant4 VMC
  • In maintenance:
    • Updates for new Geant4 releases
    • Tagged with each Root/Geant4 release that requires backward-incompatible changes
  • New features :
    • User-defined physics list enabled
    • Implements all new methods added in TVirtualMC
    • Consolidation of roottog4 converter:
      • support for positions with reflection
      • support for composite shapes
    • Extension of g4toxml converter for GDML scheme

VMC-Status and Applications

fluka vmc

Geometry

Stepping

Configuration

FLUKA

Magnetic Field

Particle Source

Stacking

Fluka VMC
  • User/Transport code interface
    • Done in traditional FORTRAN frameworks by:
      • User routines / common blocks
      • Text files (input cards)
    • TFluka hides this

communication from users

      • It follows VMC interface

design

      • Major efforts done this year to

develop and consolidate the interface

      • Still in AliRoot CVS repository, but

can be separately compiled and has

no dependency to ALICE code

      • To be moved in ROOT CVS repository

VMC-Status and Applications

class structure

TFluka

TFluka

TFluka

TFluka

TFluka

TFluka

TFluka

TFluka

TFluka

TFluka

TFlukaCutOption

TFlukaConfigOption

TFlukaCutOption

TFlukaCutOption

TFlukaConfigtOption

TFlukaConfigtOption

TFlukaConfigtOption

TFlukaCutOption

Class structure

idnrwr

g1wr

g1rtwr

conhwr

inihwr

jomiwr

lkdbwr

lkfxwr

lkmgwr

lkwr

nrmlwr

rgrpwr

isvhwr

magfld

TFlukaMCGeometry

Geometry interface

with TGeo

TVirtualMC

eedraw

endraw

mgdraw

sodraw

usdraw

source

abscff

dffcff

queffc

rflct

rfrndx

stupre

stprf

TGeoMCGeometry

Common building

methods

TFluka

Text

Input

Fluka Geometry

Navigation

Fluka User

Routines

FLUKA

VMC-Status and Applications

geometry and materials

TFluka

TFluka

TFlukaCerenkov

TFlukaMCGeometry

TGeoMaterial

TGeoMedium

Geometry and materials

alice.inp

alice.pemf

  • Before : FLUGG + GEANT4
    • Unstable / many crashes very hard to debug
  • Now : TGeo interface
    • Allowing navigation in full ALICE geometry
    • Preliminary validation steps done
    • Providing input “cards” for materials/regions
  • Material definition and assignment via FLUKA input cards
    • MATERIAL, COMPOUND, LOW-MAT and ASSIGNMAT
    • Materials defined by effective Z not accepted
  • Automatic /on-demand generation of PEMF file needed for simulation of electromagnetic processes
    • Best possible home-made solution not requiring manual intervention, but definitely not as good as fully automation of the process directly by FLUKA
  • TFlukaCerenkov to store optical properties
  • Magnetic field integrated to VMC scheme
    • Activation per region possible, but not yet implemented

VMC-Status and Applications

configuration
Configuration
  • Physics and cuts configuration used via standard FLUKA formatted input file.
    • User cuts and process switches are stored at initialization stage as arrays of objects. These are finally appended to FLUKA input
  • Solutions and open problems :
    • Primary particles retrieved from TVirtualMCStack
    • Secondaries just monitored, except particles put on stack by user code
      • Extra constraint to user stack to check for un-handled particles before tracking a new primary
    • Most switches/cuts available in VMC implemented
      • HADR=0 implemented through THRESHOLD input card
      • DCAY=0 not implemented
      • Kinetic energy cut for n, charged hadrons, muons not yet possible material-by-material

VMC-Status and Applications

stepping
Stepping

Sensitive Volume

  • Fluka user routines rewritten in C++
    • Calling TVirtualMCApplication::Stepping to notify the step
      • current track ID, current region, process ID, ...
    • Several routines for step notification
      • Energy deposition
      • Interaction
      • Normal step
      • Boundary crossing
      • Special events are notified to user code:
        • Double step for exiting and entering
        • Track resumed after secondary tracking
      • Special actions:
        • Cerenkov quantum efficiency handled at detection level

2

1

Geant 3

1: entering

1: exiting

2: entering

2: exiting

FLUKA

1: entering

1: disappeared

2: entering

2: exiting

1: entering

1:exiting

  • Special feature:different tracking sequence may influence number of hits, but not digits. Signaled anyway to user code.

2 hits 3 hits

VMC-Status and Applications

stepping actions stacking
Stepping actions, stacking
  • StopTrack() implemented for tracks in magnetic field and Cerenkov photons
  • TVirtualMCStack acts as observer and mirrors FLUKA private stack using “hook wrappers” for :
    • Particles from electromagnetic interactions
    • Particles from hadronic interactions
    • Cerenkov photons
    • Exception: Particles produced by user during stepping. Example: Feed-back photons
  • For some processes (bremsstrahlung, delta-electrons, ...), FLUKA interrupts the tracking of the mother particle in order to follow the secondary first.
    • New methodTVirtualMC::SecondariesAreOrdered()used to communicate order of secondaries to TVirtualMCStack.
  • Interfacing with TVirtualMCDecayer not yet ready

VMC-Status and Applications

tfluka g3 testing

GEANT3

FLUKA

TFluka / G3 testing
  • Behavior of AliRoot running TFluka as expected
    • Hits/digits produced in the same way as for TGeant3/TGeant4
    • No changes needed in the application specially for TFluka
      • 1 exception: stack reordering
  • Detailed analysis at detector modules level started

VMC-Status and Applications

geometry interface validation
Geometry interface validation
  • Comparison between FLUKA native stepping versus TFluka, for a simple example
  • Original setup: calorimeter sandwich Pb-Scintillator-Al, 1GeV/c protons in magnetic field
    • Vacuum put everywhere : pure geometry testing
    • Geometry reproduced identically

with TGeo

      • Boolean compositions (150 components)
      • Simple application as the ones from VMC

examples

      • Hits collected at boundary

crossings: x,y,z, track ID, region number

  • Matching procedure track-by-track
    • Computation of the distance between matching

points : dr = (PTFluka – PFLUKA) • v

VMC-Status and Applications

results
Results
  • All crossing points matching
    • Same boundary sequence
  • No magnetic field
  • B = 60 T
    • Helped fixing few bugs first
  • Very encouraging since differences

are at double-precision error level as

expected

VMC-Status and Applications

conclusions
Conclusions
  • Most efforts this year focused to the Fluka VMC part
    • Geometry interface with TGeo modeller
      • Tests done against FLUKA native geometry
    • Several developments related to configuration settings, materials, stepping and stacking
    • Ready for detailed validation
    • To be moved to ROOT CVS as all other interfaces
  • New features developed on user requests
  • Geometry converters ROOT-G4 developed
    • The only alternative at this moment for ROOT-based geometry descriptions until a solution will be found for G4+TGeo navigation
  • Continuous maintenance work

VMC-Status and Applications