Use of GEANT4 in CMS The OSCAR Project

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Use of GEANT4 in CMSThe OSCAR Project

• Isidro González
• (CERN/EP IFCA, Spain)
• for the CMS software team
• CHEP 2000, Padova, Italy
• 7-11 February 2000

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Index

• Introduction
• GEANT3.21 to GEANT4 transition
• CMS geometry model using GEANT4
• The geometry classes
• Hits and sensitive detectors
• User interaction
• Utilities
• Comparisons with Geant3.21 and data
• Conclusions

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Introduction

• GEANT4 replaces and extends GEANT3.21
• It is a modular toolkit ? Select individual parts
• Remodels the physics processes
• Better precision in prediction
• Object Oriented (C)
• CMS has implemented the geometry
• First iteration
• GUI, hits, sensitive detectors, persistency...

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GEANT3.21 to GEANT4 Transition

• CMSIM Old simulation
• FORTRAN77 GEANT3.21
• Only maintenance state

• OSCAR New simulation
• OO Simulation for CMS Analysis and Reconstruction
• C, Java GEANT4
• Will write simulated hits to OODB
• Digitisation is luminosity dependent ? Different
  package (see D. Stickland talk)

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OSCAR Milestones

• Proof of Concept Summer 1998

• Functional Prototype December 1999
• Ready shortly
• Hits persistency The possibility is there, but
  has not been implemented.
• Basic Monitoring?

• Fully Functional Prot. June 2001
• Major redesign!
• Production Version December 2003

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CMS Geometry Model using GEANT4

• Categories based on responsibilities
• Geometry categoriesCMS specific, OSCAR
  (Geant4) Persistent
• Hits categoriesCMS OSCAR
• User Interaction categoriesUser Actions, GUI
• UtilitiesMaterials, Rotation Matrices

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CMS Geometry Modelone factory - many views

• Different views are independent and consistent
• Key impact in the design

• Avoid any external dependency within the factories

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The Geometry classes

• Three categories related
• CMS Geometry
• OSCAR Geometry
• Persistent Geometry (not fully implemented)
• Polymorphic structure
• One base class
• Each sub-detector is a different class

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CMS Geometry

• Base Class CMSDetector
• Common CMS behaviour
• Handles the physical hierarchy

CMSDetector

• Each CMS sub-detector inherits from CMSDetector
  ? Easy interchange!

CMS sub-detector

• A CMS sub-detector is a store of geometry
  information
• Build something fast ? No geometry description
  language ( free storage format)

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CMS Geometry
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OSCAR Geometry

• Base Class G4Able
• Common GEANT4 behaviour
• Sensitive property
• Visualisation attributes

OSCAR sub-detector
? Run time selection!
G4 Able

• OSCAR sub-detector extends CMS sub-detector

CMS sub-detector

• Complex architecture!
• No G4 knowledge in CMS

• OSCAR sub-detector inherits from G4Able and
  CMSsub-detector

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OSCAR Geometry examples
Barrel Pixel Barrel SVTX Preshower
Forward Pixel Barrel HCAL
HCAL Test-Beam
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Persistent Geometry

• ASCII files exist for all sub-detectors
• CMS Geometry is the path to Objectivity and
  GEANT4
• A framework to make detectors persistent exists
• Only few detectors have been made persistent

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Hits and Sensitive Detectors

• 2 type of sensitive detectors
• Tracker-like
• Calorimeter-like

• which produce hits
• Compatible with ORCA
• Stored in hits collections

• Base classes
• 2 OSCAR sensitive detectors
• 2 types of CMS hits
• 2 types of OSCAR hits

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User Interaction

• User Actions required by GEANT4
• Detector construction CMS full detector,
  test-beams
• Physics list List of physics processes. Not
  trivial? ?Needs improvement!
• Primary generator Extended with...
• Single particle generation in random direction
• Possibility to read events from PYTHIA files

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Optional User Action classes in CMS

• Optional User Action
• Run
• Event
• Tracking
• Stepping

• Extended with action units Independent pieces of
  behavior
• Action units can be plugged in each action

Extra behavior added easily!
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Utilities

• Materials Factory
• Extend GEANT4 material constructors (materials
  composed of other materials)
• Avoid multiple instances
• Rotation Matrices Factory
• Extend GEANT4 rotation matrix constructors
• Avoid multiple instances

• Magnetic Field Same model as in Geometry
• CMS implementation independent from GEANT4
• OSCAR implementation extends CMS

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Physics Validation

• ECAL crystals in Geant3 and Geant4 Test of
  electromagnetic processes

30 GeV photons. No magnetic field
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Comparison withtest-beam data

• HCAL Test-Beam
• Simulation run with no tuning at all
• Very preliminary analysis!
• More detailed comparisons on the way...

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Conclusions

• A functional prototype of a GEANT4 based
  simulation will be ready soon
• An extensible and flexible model for the geometry
  and hits has been implemented
• We extended GEANT4 to our needs
• Tracking through the whole CMS is possible
• Hits are produced for most of the detectors
• Comparisons with data and GEANT3.21 have been
  started