1. The New ROOT Geometry Package
RTAG MC
CERN 8 August
René Brun, Andrei & Mihaela Gheata
CERN
ftp://root.cern.ch/root/rootgeom.ppt
ROOT Geometry PackageL

2. Simulation tools Geant3 Geant4 Fluka created in 1981 Still used by
the majority
of experiments
Geant4
A huge investment
Slow penetration
in experiments
Fluka
State of the art
for hadronics
and neutron physics
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ROOT Geometry Package

3. Detector Geometry (way 1)
Simulation
program
Geant4-based
C++
classes
Geant4
geometry
Visualisation
XML
files
Reconstruction
program
MySQL
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ROOT Geometry Package

4. The Virtual MonteCarlo
For example
AliRoot
in Alice
This strategy facilitates
migration or comparisons
with a common input
and a common output
DAQ
Online
Geant3
Kinematics
Geometry
Geant4
Fluka
TVirtualMC
Geant3.tar.gz includes
an upgraded Geant3
with a C++ interface
Hits, Digits
Geant4_mc.tar.gz includes
the TVirtualMC <-->Geant4
interface classes
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ROOT Geometry Package

5. Virtual MC example (with G3){
// Load basic libraries
gSystem->Load("libPhysics");
gSystem->Load("libMC");
gSystem->Load("$(MCINSTALL)/lib/Linux-g++/libexample01");
// Load Geant3 libraries
// … skipped
// MC application
Ex01MCApplication* appl
= new Ex01MCApplication("Example01", "The example01 MC application");
appl->InitMC("g3Config.C");
appl->RunMC(1); }
void Config() g3Config.C {
cout << "Create geant3" << endl;
new TGeant3("C++ Interface to Geant3"); }
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ROOT Geometry Package

6. Virtual MC example (with G4){
// Load basic libraries
gSystem->Load("libPhysics");
gSystem->Load("libMC");
gSystem->Load("$(MCINSTALL)/lib/Linux-g++/libexample01");
// Load Geant4 libraries
// … skipped
// MC application
Ex01MCApplication* appl
= new Ex01MCApplication("Example01", "The example01 MC application");
appl->InitMC("g4Config.C");
appl->RunMC(1); }
void Config() { g4Config.C
// RunConfiguration for Geant4
TG4RunConfiguration* runConfiguration = new TG4RunConfiguration();
// TGeant4
new TGeant4("TGeant4", "The Geant4 Monte Carlo", runConfiguration); }
R.Brun RTAG MC
ROOT Geometry Package

7. Detector Geometry (way 2)
Modelling
Visualisation
Interactivity
Where am I?
Distance to boundary
Closest boundary
Persistency
Simulation
program
Geant3-based
Geant4-based
Fluka-based
C++
classes
Geometry
package
MySQL
Reconstruction
program
Visualisation
R.Brun RTAG MC
ROOT Geometry Package

8. The new ROOT Geometry package
Was the request Nr 1 at ROOT FNAL workshop in June 2001
The package is being developed in collaboration with Alice (Andrei & Mihaela Gheata)
Alpha release in July
faster than Geant3
Import from Geant3 (eg 4 LHC detectors)
Interfaces to Geant3,4, Fluka in view
Demos on request
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ROOT Geometry Package

9. The TGeo classes in html http://root. cern. ch/root/htmldoc/ClassIndex
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ROOT Geometry Package

10. TGeoManager
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ROOT Geometry Package

11. TGeoShape
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ROOT Geometry Package

12. TGeoVolume
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ROOT Geometry Package

13. TGeoNode
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ROOT Geometry Package

14. Example
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ROOT Geometry Package

15. The ROOT “detector” example
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ROOT Geometry Package

16. Shooting random points
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ROOT Geometry Package

17. Shooting random rays
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ROOT Geometry Package

18. Automatic conversion from Geant3
Zebra memory
Data structure
JVOLUM
JMATE,etc
Root > .x mygeom.C
Mygeom.c
void gexam1()
{TGeoMaterial *mat;
TGeoMixture *mix;
TGeoManager *gexam1 = new TGeoManager("gexam1","gexam1.C");
// List of Materials and Mixtures
mat = new TGeoMaterial("mat9","ALUMINIUM",26.98,13,2.7);
mix = new TGeoMixture("mix10","IRON(COMPOUND)",3);
mix->DefineElement(0,55.847,26, );
mix->DefineElement(1,58.71,28, E-01);
mix->DefineElement(2,51.998,24,0.197);
mat = new TGeoMaterial("mat11","COPPER",63.54,29,8.96);
Geant > RZ/File 21 mygeom.geom on
Zebra RZ
mygeom.geom
g2root mygeom.geom mygeom.C
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ROOT Geometry Package

19. generated automatically
Example : gexam1
// List of Volumes
TGeoVolume *ECAL ;
ECAL = gexam1-> MakeTube("ECAL","mat15",0, , );
LEAK = gexam1->MakeTube("LEAK","mat15",0, , );
LATR = gexam1->MakeTube("LATR","mat15", ,5.813,11.23);
BLOC = gexam1->MakeTube("BLOC","mix21",0, , );
// List of Nodes
gexam1->SetTopVolume(ECAL);
ECAL->AddNode(LEAK,1,new TGeoTranslation(0,0, ));
ECAL->AddNode(LEAK,2,new TGeoTranslation(0,0, ));
ECAL->AddNode(LATR,1,gGeoIdentity);
ECAL->AddNode(BLOC,1,gGeoIdentity);
TGeoVolume *RTUB = BLOC->Divide("RTUB",1,20,0, );
TGeoVolume *RING = RTUB->Divide("RING",3,20,-11.31,1.131);
gexam1->CloseGeometry(); }
void gexam1() {
TGeoMaterial *mat;
TGeoMixture *mix;
TGeoManager *gexam1;
gexam1 = new TGeoManager("gexam1","gexam1.C");
// List of Materials and Mixtures
mat = new TGeoMaterial("mat9","ALUMINIUM",26.98,13,2.7);
mix = new TGeoMixture("mix10","IRON(COMPOUND)",3);
mix->DefineElement(0,55.847,26, );
mix->DefineElement(1,58.71,28, E-01);
mix->DefineElement(2,51.998,24,0.197);
mat = new TGeoMaterial("mat11","COPPER",63.54,29,8.96);
mat = new TGeoMaterial("mat13","LEAD",207.19,82,11.35);
mat = new TGeoMaterial("mat14","URANIUM",238.03,92,18.95);
mat = new TGeoMaterial("mat15","AIR",14.61,7.3,0.1205E-02);
mat = new TGeoMaterial("mat16","VACUUM",0,0,0);
mix = new TGeoMixture("mix21","BGO(COMPOUND)",3);
mix->DefineElement(0,208.98,83, );
mix->DefineElement(1,72.59,32, );
mix->DefineElement(2,15.999,8, );
mix = new TGeoMixture("mix22","LEAD GLASS",6);
mix->DefineElement(0,207.19,82, );
mix->DefineElement(1,39.102,19, E-02);
mix->DefineElement(2,28.088,14, );
mix->DefineElement(3,22.99,11, E-02);
mix->DefineElement(4,15.999,8, );
mix->DefineElement(5,74.922,33, E-02);
gexam1.C code
generated automatically
by g2root
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ROOT Geometry Package

20. Brahms
2649 nodes
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ROOT Geometry Package

21. CMS
1.3 million nodes
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ROOT Geometry Package

22. Atlas
29 million nodes
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ROOT Geometry Package

23. Atlas
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ROOT Geometry Package

24. Atlas
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ROOT Geometry Package

25. Alice
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ROOT Geometry Package

26. Alice
3 million nodes
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ROOT Geometry Package

27. TGeo performance vs Geant3
Number gtmedi Root Geant3/ gtmedi Root Geant3/
nodes physics physics Root random random Root
Gexam
Gexam
Gexam
Brahms
Tesla
CDF
Minos_near
BTeVEcal
BTeV
CMSEcal
CMS
LHCb
Alice
Atlas
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ROOT Geometry Package

28. BteV
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ROOT Geometry Package

29. Validation Procedure Use one million points generated by Geant3.
Compare G3 path vs TGeo found path (pictures for a CDF event)
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ROOT Geometry Package

30. Validation Procedure Using points generated by Geant3 applications
grecord.f --> mygeom.geom, mygeom.hbook
Play-back these points in Geant3 using only the Geant3 geometry package. Compute g3path, snext, safety in myresults.hbook
h2root myresults.hbook myresults.root
Same operation with TGeo classes. Compare g3path with tgeopath, same for snext, safety
Some discrepancies with Geant3 (see next)
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ROOT Geometry Package

31. Validation Procedure Differences Geant3 TGeo
Due to precision problems in Geant3, points recorded at the volume boundaries may be found on the other side by TGeo.
When volumes declared MANY in Geant3 overlap and have sub-volumes also MANY, Geant3 is not always reporting the right answer. In general it does not matter, sometimes it does.
In this exercise, we also found original errors in the detector description, eg wrong parameters.
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ROOT Geometry Package

32. Status of the implementation - test of gtnext
Visualization - best tool for checking the algorithms
The "width" of the boundaries due to floating point limitations was determined for some shapes
This diffusion effect is crucial for fixing stepping actions in order to trigger expected inside/ouside response of the modeler
The diffusion was defined as the distance between extrapolated point from step and closest point that changes this in/out response.
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ROOT Geometry Package

33. Status of the implementation
Geant3 geometries - almost fully mapped (still not supporting multiple positioning for volumes having shapes with negative parameters which then are divided - quite seldom topology)
"Where am I ?" - fully implemented
Tested on a dozen of geometries, including all 4 LHC experiments
Performance w.r.t GEANT3 - OK. The average gain factor ~ , increasing for flat-like geometries
Consistency vs. GEANT3 response reasonable : still few % differences, but fully understood
Still scope for increasing speed, specially for cylindrical symmetries, where the current voxelization algorithm is not efficient enough.
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ROOT Geometry Package

34. Status of the implementation - gtnext
"Which is the next crossed boundary ?" - about 80% implemented, still a couple of weeks to work on it.
Algorithms per shape improved w.r.t G3 for some shapes
New functionalities added : normals to surfaces at crossing points, accurate distance to closest node, direction vector to closest point
Features for stepping added : flags for entering and exiting
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ROOT Geometry Package

35. Summary The new Geometry Package looks very promising.
We have been able to model all existing large detectors.
Performance is better than Geant3.
We are planing to interface it via TVirtualMC to Geant3, Geant4 and Fluka.
Alpha release with ROOT version 3.03/07
R.Brun RTAG MC
ROOT Geometry Package