1. Use of GEANT4 in CMS The OSCAR Project
Isidro González
(CERN/EP & IFCA, Spain)
for the CMS software team
CHEP 2000, Padova, Italy
7-11 February 2000

2. Isidro González, CERN/EP & IFCA
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
9 May 2019
Isidro González, CERN/EP & IFCA

3. Isidro González, CERN/EP & IFCA
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...
9 May 2019
Isidro González, CERN/EP & IFCA

4. 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)
9 May 2019
Isidro González, CERN/EP & IFCA

5. Isidro González, CERN/EP & IFCA
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
9 May 2019
Isidro González, CERN/EP & IFCA

6. CMS Geometry Model using GEANT4
Categories based on responsibilities
Geometry categories: CMS specific, OSCAR (Geant4) & Persistent
Hits categories: CMS & OSCAR
User Interaction categories: User Actions, GUI
Utilities: Materials, Rotation Matrices
9 May 2019
Isidro González, CERN/EP & IFCA

7. CMS Geometry Model: one factory - many views
Different views are independent and consistent
Key impact in the design
CMS
Tracker
ECAL
...
Factories
Simulation
Reconstruction
Visualisation
Avoid any external dependency within the factories
9 May 2019
Isidro González, CERN/EP & IFCA

8. Isidro González, CERN/EP & IFCA
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
9 May 2019
Isidro González, CERN/EP & IFCA

9. Isidro González, CERN/EP & IFCA
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)
9 May 2019
Isidro González, CERN/EP & IFCA

10. Isidro González, CERN/EP & IFCA
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 CMS sub-detector
9 May 2019
Isidro González, CERN/EP & IFCA

11. OSCAR Geometry: examples
Barrel Pixel Barrel SVTX Preshower
Forward Pixel Barrel HCAL
HCAL Test-Beam
9 May 2019
Isidro González, CERN/EP & IFCA

12. Isidro González, CERN/EP & IFCA
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
9 May 2019
Isidro González, CERN/EP & IFCA

13. 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
9 May 2019
Isidro González, CERN/EP & IFCA

14. Isidro González, CERN/EP & IFCA
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
9 May 2019
Isidro González, CERN/EP & IFCA

15. Optional User Action classes in CMS
Run
Event
Tracking
Stepping
Extended with action units: Independent pieces of behavior
Action units can be plugged in each action
Extra behavior added easily!
9 May 2019
Isidro González, CERN/EP & IFCA

16. Isidro González, CERN/EP & IFCA
Utilities
Materials Factory:
Extend GEANT4 material constructors (materials composed of other materials)
Avoid multiple instances
Rotation Matrices Factory:
Extend GEANT4 rotation matrix constructors
Magnetic Field: Same model as in Geometry
CMS implementation independent from GEANT4
OSCAR implementation extends CMS
9 May 2019
Isidro González, CERN/EP & IFCA

17. Physics Validation
ECAL crystals in Geant3 and Geant4: Test of electromagnetic processes
30 GeV photons. No magnetic field
9 May 2019
Isidro González, CERN/EP & IFCA

18. Comparison with test-beam data
HCAL Test-Beam
Simulation run with no tuning at all
Very preliminary analysis!
More detailed comparisons on the way...
9 May 2019
Isidro González, CERN/EP & IFCA

19. Isidro González, CERN/EP & IFCA
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
9 May 2019
Isidro González, CERN/EP & IFCA