1. Pedro Arce (CERN/CIEMAT) (on behalf of CMS collaboration)
GEANT4 CMS SIMULATION
Pedro Arce (CERN/CIEMAT)
(on behalf of CMS collaboration)
GEANT4 workshop 02
CMS GEANT4 Simulation Pedro Arce (CERN/CIEMAT)

2. CMS GEANT4 Simulation Pedro Arce (CERN/CIEMAT)
Outline
OSCAR functionality
OSCAR/GEANT4 robustness and performance
Physics comparisons
GEANT4 workshop 02
CMS GEANT4 Simulation Pedro Arce (CERN/CIEMAT)

3. OSCAR functionality: Geometry
All CMS detectors
Also several Testbeams
Currently moving to geometry in XML database, common to Simulation/Reconstruction/Visualisation
All geometry converted from GEANT3 geometry
Building of XML geometry into GEANT4 ready
Already can be visualised with IGUANA (heavily used for debugging)
Missing: detector numbering schemes with new geometry
Will need to review the use of ‘SetSmartLess’ (3 years old)
Detailed checking quite advanced
Thorough comparison of GEANT3 and GEANT4 geometry
All materials, volumes and touchables properties
Positions of touchable centres
Material budget
CMS Overlap Detection Tool (now in GEANT4)
GEANT4 workshop 02
CMS GEANT4 Simulation Pedro Arce (CERN/CIEMAT)

4. CMS GEANT4 Simulation Pedro Arce (CERN/CIEMAT)
Geometry for OSCAR
XML based Detector
Description Language
(XML DDL)
- Single description inter-
face for the ideal detector
- Generic description
. Materials
. Geometry
. Component approach
- Attaching specific
Information to
. Components
. Subsets of Volumes
- Human editable/readable
/expandable
GEANT4 workshop 02
CMS GEANT4 Simulation Pedro Arce (CERN/CIEMAT)

5. View of 180 Higgs event simulated in CMS Tracker detector
Sliced view of CMS barrel detectors
View of CMS muon system
View of 180 Higgs event simulated in CMS Tracker detector
GEANT4 workshop 02
CMS GEANT4 Simulation Pedro Arce (CERN/CIEMAT)

6. OSCAR functionality: Primary generator
CMS particle gun:
Scan in , , energy
Random (flat/gaussian) in , , energy
Interface with HEPEVT ASCII files
Interface with PYTHIA ntuples
Long-life particles:
In GEANT3 only the decay products are simulated
In GEANT4 the particle is simulated before decaying (and the decay products are kept)
Advantage: you take into account the possibility of interactions, energy loss, magnetic field bending, etc. before decaying
The life time is not kept
The momentum of decay products is not kept
OSCAR: user can select to simulate the particles before decaying or simulate decay products (keeping the life time)
Need deeper study to understand what will be the final solution
GEANT4 workshop 02
CMS GEANT4 Simulation Pedro Arce (CERN/CIEMAT)

7. OSCAR functionality: Persistency
Hits for all detectors
Primary generator particles
Selected tracks
Use CMS framework (COBRA)
Fully compatible with Reconstruction
Using Objectivity, moving to ROOT (end 2002)
GEANT4 workshop 02
CMS GEANT4 Simulation Pedro Arce (CERN/CIEMAT)

8. OSCAR functionality: Visualisation
Interactive visualisation is done with IGUANA
Visualise any GEANT4 Geometry
Select by logical volumes / by physical volumes
Picking, slices
Volume property window
GEANT4 command line
A wizard to guide through OSCAR settings
Adding other extensions is trivial (e.g. GUIs like overlap detection)
Visualise Tracks
Visualise magnetic field
Integrated with overlap detection
Find overlaps, show result details in a list
Highlight overlaps in 3D
Hits, in the near future
GEANT4 workshop 02
CMS GEANT4 Simulation Pedro Arce (CERN/CIEMAT)

9. Example extension (a trivial wizard) IGUANA viewer displaying
OSCAR - IGUANA
Overlap detection
Example extension (a trivial wizard)
Queried from plug-in database, loaded on request and bound to IGUANA G4 Run Manager
Control of arbitrary
GEANT4 tree
Correlated
Picking
IGUANA viewer displaying
OpenInventor scene
GEANT4 workshop 02
CMS GEANT4 Simulation Pedro Arce (CERN/CIEMAT)

10. OSCAR - IGUANA: magnetic field
2D plane that can be rotated
Field direction as an arrow
Field intensity as colour
GEANT4 workshop 02
CMS GEANT4 Simulation Pedro Arce (CERN/CIEMAT)

11. OSCAR functionality Physics:
Electromagnetic processes needed at LHC
Hadronic processes needed at LHC
CMS Physics Technical Design Report is planned to be written using OSCAR (due end 2005)
OSCAR milestone Spring/Summer 2003:
“Reproduce the physics results of the GEANT3 simulation with similar performance”
Physics Cuts:
Production cuts per material
Minimum kinetic energy cuts per material
Still under investigation if we really need them
Time of flight cut
GEANT4 workshop 02
CMS GEANT4 Simulation Pedro Arce (CERN/CIEMAT)

12. CMS GEANT4 Simulation Pedro Arce (CERN/CIEMAT)
OSCAR functionality
UserActions:
Several user actions of the same type loadable on demand
Framework:
COBRA manages the main() and takes care of persistency
Now OSCAR is being reengineered to achieve full integration with CMS Framework (see wednesday talk by M. Stavrianakou)
Documentation:
User’s Guide updated for each release
doxygen documentation
Several Tutorials on the web
For OSCAR developers
For Physics Reconstruction software developers
For Summer Students
GEANT4 workshop 02
CMS GEANT4 Simulation Pedro Arce (CERN/CIEMAT)

13. OSCAR is ready for physics validation studies
OSCAR functionality
Future developments:
GEANT4e as GEANE replacement (error propagation for track fitting)
Under progress
GFLASH for fast simulation
RTAG/G4 discussion
Summary:
OSCAR is ready for physics validation studies
GEANT4 workshop 02
CMS GEANT4 Simulation Pedro Arce (CERN/CIEMAT)

14. OSCAR/GEANT4 robustness
Several problems found:
Particles loop between two volumes
 push them by 0.01 mm
Several G4Exception found:
solved by CMS team or/and with the help of GEANT4 team
>10000 pp events without crashing
NOTE: new G4Exception found with GEANT4.4.1 (under investigation)
GEANT4 workshop 02
CMS GEANT4 Simulation Pedro Arce (CERN/CIEMAT)

15. GEANT4 vs GEANT3 Time Performance
- Full events: H / tte / Z
- Cuts in primary particles: Pt : 1 GeV, || < 2.4 (3.0)
- Full CMS geometry
- 3D TOSCA magnetic field
- Production and tracking cuts as in CMSIM (GEANT3)
- GEANT4 voxel navigation
- GEANT4.4.0.ref02
- Pentium III 850 Mhz
- Checked that they are really the same events (see next)
GEANT4 workshop 02
CMS GEANT4 Simulation Pedro Arce (CERN/CIEMAT)

16. CMS GEANT4 Simulation Pedro Arce (CERN/CIEMAT)
G3-G4 events detailed comparison
H in all CMS (10 Events)
Initial track energy
No Tracks
MeV
Track length
No Tracks mm
GEANT4 workshop 02
CMS GEANT4 Simulation Pedro Arce (CERN/CIEMAT)

17. CMS GEANT4 Simulation Pedro Arce (CERN/CIEMAT)
G3-G4 events: detailed comparison
Origin of secondary tracks: R vs Z
R (mm)
CMSIM
( tracks)
Z (mm)
R (mm)
OSCAR
( tracks)
Z (mm)
GEANT4 workshop 02
CMS GEANT4 Simulation Pedro Arce (CERN/CIEMAT)

18. CMS GEANT4 Simulation Pedro Arce (CERN/CIEMAT)
Time performance
- H (10 events)
CMSIM: 439k tracks sec/evt
OSCAR: 400k tracks sec/evt (1.83)
- tte (10 events)
CMSIM: 1809k tracks sec/evt
OSCAR: 1159k tracks sec/evt (2.31)
- Z (10 events)
CMSIM: 1105k tracks sec/evt
OSCAR: 941k tracks sec/evt (2.58)
GEANT4 workshop 02
CMS GEANT4 Simulation Pedro Arce (CERN/CIEMAT)

19. CMSIM(GEANT3) - OSCAR(GEANT4) comparison Central Tracker
Number of rechits per track vs eta
Cmsim 122
OSCAR pre 03
RecHits
100 GeV Pt muons in region ||<2.5
resolution vs eta
GEANT4 workshop 02
CMS GEANT4 Simulation Pedro Arce (CERN/CIEMAT)

20. CMSIM(GEANT3) - OSCAR(GEANT4) comparison: Muon System
reconstructed – generator quantities
5-200 GeV Pt muons in region ||<2.4
GEANT4 workshop 02
CMS GEANT4 Simulation Pedro Arce (CERN/CIEMAT)

21. Importance of tuning tracking precision parameters
Big difference between reconstructed and generated track parameters was found because tracking precision parameters were too high.
‘deltaIntersectionAccuracy’
is by default 100 m
CMS tracker precision 20 m
CMS Muon prcision 200 m
Has to be set to 0.1 m
Time just increased by 3%
GEANT4 workshop 02
CMS GEANT4 Simulation Pedro Arce (CERN/CIEMAT)

22. CMSIM(GEANT3) - OSCAR(GEANT4) comparison: EM calorimeter
SETUP:
CMS electromagnetic calorimeter: lead tungstate crystals pointing to interaction point
Photon of E = 30 GeV enters front face of crystal
No magnetic field
What was compared:
E in hottest crystal, in 3x3, in 5x5 matrix
E total
dNhits/dt, for 1 ns time slices
GEANT3.21 vs GEANT4.4.0.p02
GEANT4 workshop 02
CMS GEANT4 Simulation Pedro Arce (CERN/CIEMAT)

23. CMSIM(GEANT3) - OSCAR(GEANT4) comparison: EM calorimeter
Shower containment:
From GEANT4 gallery:
Electron 5 Gev in PbWO4
(more detailed)
GEANT3 looks wider than GEANT4
From old test beam GEANT3/GEANT4 comparison
CMS Note 1997/037 by A.Givernaud: good agreement with G3 for shower profile
CMS Note 1998/031 by K.Lassila-Perini: G3 shower is a bit wider than real shower
GEANT4 workshop 02
CMS GEANT4 Simulation Pedro Arce (CERN/CIEMAT)

24. CMSIM(GEANT3) - OSCAR(GEANT4) comparison: EM calorimeter
Hit timing:
GEANT4 shower has ~8% less hits than GEANT3 shower
It doesn´t contradict with
GEANT4 gallery plot below,
however direct comparison is needed:
GEANT4 workshop 02
CMS GEANT4 Simulation Pedro Arce (CERN/CIEMAT)

25. ECAL + HCAL testbeam: GEANT3 - GEANT4 comparison
1996 Testbeam Setup for CMS HCAL
A test module of copper absorber plates with scintillator tile sampling
28 scintillator plates with absorber of varying thickness in between
A prototype lead tungstate crystal electromagnetic calorimeter
Energies: 225 GeV  (for calibration), GeV , GeV e-
Magnetic Field: 0, 0.75, 1.5, 3 tesla (direction parallel to the face of the scintillator)
Configuration: Only HCAL or ECAL + HCAL
5000 events were taken for each setup
Response of the Calorimeter was studied as a function of:
Magnetic field: effect on scintillator
Absorber thickness: optimisation of resolution versus containment
Absorber depth: energy containment
Electromagnetic Calorimeter contribution: e/ effects
GEANT4 workshop 02
CMS GEANT4 Simulation Pedro Arce (CERN/CIEMAT)

26. ECAL + HCAL testbeam: GEANT3 - GEANT4 comparison
GEANT4 4.0.p02
100 GeV pi Tesla ECAL+HCAL
GEANT4 workshop 02
CMS GEANT4 Simulation Pedro Arce (CERN/CIEMAT)

27. ECAL + HCAL testbeam: GEANT3 - GEANT4 comparison
100 GeV e Tesla HCAL
GEANT4 workshop 02
CMS GEANT4 Simulation Pedro Arce (CERN/CIEMAT)

28. ECAL + HCAL testbeam: GEANT3 - GEANT4 comparison
pi Tesla ECAL+HCAL
Events with MIP in ECAL
Events with shower in ECAL
GEANT4 workshop 02
CMS GEANT4 Simulation Pedro Arce (CERN/CIEMAT)

29. ECAL + HCAL testbeam: GEANT3 - GEANT4 comparison
pi Tesla ECAL+HCAL
Events with MIP in ECAL
Events with shower in ECAL
GEANT4 workshop 02
CMS GEANT4 Simulation Pedro Arce (CERN/CIEMAT)

30. CMS GEANT4 Simulation Pedro Arce (CERN/CIEMAT)
Summary
OSCAR is technically complete to start with physics studies
Some comparisons vs CMS GEANT3 simulation started
Some problems found, but solved by CMS + GEANT4
Some TestBeam comparisons started:
Show reasonable agreement with data
Slightly better than GEANT3
Others to be done: ECAL TB ‘99, ECAL TB ‘02, ECAL+HCALTB ‘99, HCAL ‘02, Tracker ´02
Next months: systematic comparison with GEANT3 simulation
Plan to move to GEANT4 simulation by Summer 2003
GEANT4 workshop 02
CMS GEANT4 Simulation Pedro Arce (CERN/CIEMAT)