Use of G EANT 4 in CMS AIHENP’99 Crete, 12-16 April 1999 Véronique Lefébure CERN EP/CMC.

Use of GEANT4 in CMS

AIHENP’99Crete, 12-16 April 1999

Véronique LefébureCERN EP/CMC


Véronique LEFEBURECERN EP/CMC

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Content

• The CMS Experiment

• The GEANT4 Toolkit

• CMS first experience using GEANT4

• Summary



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CMS: Compact Muon Solenoid

– CERN, LHC, 2005– ~20000 particles / 25 nanoseconds– Complex detector, 22 m long, 15 m diameter– World-wide collaboration of ~ 1600 physicists



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The CMS detector

Central tracking

Electromagneticcalorimeter

Hadron calorimeter

SolenoidMuon system

Beam-Pipe



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CMS Simulation Needs

Simulation is needed for– detector engineering studies and optimization

– determination of trigger logic

– estimation of potential for physics discoveries

– interpretation of the experimental data

simulation of– detector geometry

– particle interactions in the detector material

– detector response



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OSCAR (GEANT4) ORCA

HIT

Tracking

Xin

Xout

ΔE

Digitization

DIGI

Simulation of the

Detector Response

Clusterization of Digi’s

+Pattern Recognition

Reconstruction

TrackRHIT



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The GEANT4 Toolkit1. Introduction

– GEANT4.0.0 was released in January 1999 : 4 year R&D,

> 100 physicists, engineers, computer scientists, ~40 institutes

– Complete toolkit of electromagnetic and hadronic physics, solid modeling, tracking, run and event generation, visualization, GUI

– Designed and implemented with Object-Oriented technologies (C++)

– Meeting requirements for LHC experiments

– User extensible

– ESA joint-project (spacecraft's and instrumentation design, radiation shielding) + nuclear and medical applications



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The GEANT4 Toolkit2. Functionality

– Description of the geometry and material composition of the detector

• CMS: several 100K physical volumes, ~50 different shapes, ~200 materials

– Particles are tracked through the detector, simulating their physics interactions in matter and the effect of fields and boundaries on their trajectories

• CMS: 4 T magnetic field

– Graphics, user interfaces, object storage

• CMS: storage of geometry information and simulated hits to be used by ORCA



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The GEANT4 Toolkit3.Physics

– Physics modeling• is transparent to the user

• can be extended by the user

– Cross-sections and final states• are computed separately from the tracking system

• can be split by energy range, particle type and material

– Cross-sections determine the tracking step length– Use of an extensive system of units



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The GEANT4 Toolkit4. Architecture

RUN

EVENT

TRACKING

TRACK

GEOMETRY

FIELDS

READOUT

DIGI

HITS

CAD

GENERATORS

PHYSICS

PARTICLE

MATERIAL

GUI & UI

Visualization

ODBMS

Utilities



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CMS Geometry Simulation:1.Architecture

Tracker

Beam-Pipe

Calorimeters

Muon System

CMS

Tracker

Barrel Si Pixel

Forward Si Pixel

Forward Si Strip

Barrel Si Strip

Forward MSGC

Barrel MSGC



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CMS Geometry Simulation:1.Architecture (cont’d)

Barrel Si Pixel Support

Cables

Services

•Cooling system•Set of Replicated structure made of

•Support•Set of Replicated assembly made of

•sensitive volume•electronics•cables

X 2 layers



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CMS Barrel Si Pixel

GEANT4.0.0max. radius = 11 cmlength = 60 cm



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CMS Geometry Simulation:2.Implementation

– Mother-Daughter organization: construction is propagated from mother to daughters

– First prototype: access to input data de-coupled from construction of GEANT4 geometry, only knowledge of shapes.

CMSDetectorconstructinput filelist of daughters BarrelPixel

specific parameters

G4BarrelPixelspecific shapes

G4Ableconstructset sensitivityset visual attributes



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CMS Geometry in GEANT4current status

• Beam Pipe • Tracker

– Si Pixel Detectors• Barrel Si Pixel • Forward Si Pixel

– Si Strip Detectors • Barrel Si Strip

– MSGC • Barrel MSGC

• Calorimeters – Electromagnetic Calorimeter

• Barrel ECAL – Hadron Calorimeter

• Barrel HCAL • Muon System

– Barrel Muon



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CMS Materials

• GEANT4:– Materials defined by weight fractions or atom

proportions, of elements and/or materials

• CMS has developed:– Material definition based on mixtures of elements

and/or mixtures of materials, by weight fraction, volume fraction, atomic proportions. CMSMaterial and CMSMaterialFactory (input file)



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CMS Rotation Matrices

• GEANT4:– Matrix constructed from Identity, rotation axes and

angles (from CLHEP)

• CMS has developed:– Matrix specified by polar and azimuthal angles of

the new axes. CMSRotationMatrixFactory (input file)



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CMS Magnetic Field Map

G4Field

G4MagneticField

G4UniformMagneticField G4CMSMagneticField

CMSMagneticField

G4FieldManager1 1 .. n



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Magnetic Field in CMS



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Muon Physics with GEANT4

Comparisons between GEANT3.21and GEANT4.0.0 for low/high energy muons going through 100 cm iron.

– Good agreement for E~10 GeV– Differences at E~100 GeV as expected:

• limit of validity range of GEANT3, process missing, correction factors missing

• GEANT4 uses more up-to-date cross-section values

– Results going to be compared with experimental data



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Muon mult. scattering

Transverse displacementafter 100 cm ironGEANT3.21 :GEANT4.0.0 :

10 GeV muons

100 GeV muons

mm

mm



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Muon energy loss

Energy loss in 100cm ironGEANT3.21 :GEANT4.0.0 :

10 GeV muons

100 GeV muons

MeV

MeV



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HCAL (H2 1996) Test-Beam Setup

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27

Layer 1 1 : 2 cm Copper

Layers 22 to 7 : 3 cm Copper

Layers 8 to 21: 6 cm Copper

Layers 22 to 27: 8 cm Copper

Scintillators: 2 mm passive Plastic

4 mm active Plastic

1 mm passive Plastic

152 cm Copper + 189 mm Plastic

64 cm x 64 cm



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G4 Hadronic showers



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50 GeV pion shower



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Summary

• CMS has close to 2 year experience with alpha, beta and first public releases of GEANT4

• GEANT4 will be used for full CMS simulation (OSCAR project)

• further validation tests of the physics processes simulated by GEANT4 will be performed using test-beam data

Use of G EANT 4 in CMS AIHENP’99 Crete, 12-16 April 1999 Véronique Lefébure CERN EP/CMC.

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