LCDG4: a Geant4-based detector simulator for the LCD

1. LCDG4: a Geant4-based detector simulator for the LCD Guilherme Lima for the NICADD simulations group Geant4 Tutorial Fermilab, Oct.28 2003

2. Outline • NICADD • Linear Collider and LCD • Detector simulation • Requirements • Implementation details • Event displays • Status

3. NICADD • Northern Illinois Center for Accelerator and Detector Development • Research and Developments for the next Linear Collider (LC) • Detectors: design, development, prototyping, testing and construction of a sampling, scintillator-based digital hadronic calorimeter • Simulation and software developments by Dhiman Chakraborty (coordinator), Guilherme Lima, Jeremy McCormick, Vishnu Zutshi • More information at http://nicadd.niu.edu

4. Linear Collider • Electron-positron collisions at 500 to 1000 GeV • Luminosities of 1034 cm-2 s-1 • Physics motivation: Precision studies: Higgs, supersymmetry and other new phenomena • Possible e-e-, e-g and gg configurations • Accelerator technology and site not yet chosen • Start date: around 2015 • Overlap with LHC is desirable

5. Detector geometry SDJan03 • Some versions under study • SD detector • LD detector • PD detector • Detector components • VXD (vertex detector) • Tracker • EM calorimeter • Hadronic calorimeter • Luminosity detector • Solenoid coil • Muon system

6. Options under study: SD, LD, PD

7. A Digital Hadronic Calorimeter?

8. Simulation of a digital HCal • High segmentation for better energy resolution: one bit (digital) or two bits (semidigital) per cell • Questions to be addressed • Cell shapes (squares, rectangles, hexagons) • Cell dimensions (digital calorimeter) • Projective vs. non-projective calorimeters • Sampling fractions (number of layers, active to absorber ratios) • Cost / performance optimization

9. Detector Simulation • Support the detector design activities at NICADD • Useful tool for the whole LCD collaboration • Some basic requirements: • Flexible geometry description • Input from binary STDHEP • Output in LCD-specific formats (sio, lcio) • Hits should be associated to MC particles

10. Geant4 implementation • G4RunManager • UserInitialization • PhysicsList • LCDXML2G4DetConst (detector construction) • UserAction • LCDG4PrimaryGeneratorAction • LCDG4EventAction • LCDG4SteppingAction • LCDG4TrackingAction • G4VisManager • G4UIManager

11. PhysicsList Basically inherited from Mokka (See http://polype.in2p3.fr/geant4/tesla/www/mokka/mokka.html) • GeneralPhysics charged, neutral geantinos, and all decays • EMPhysics e+, e-, g, ne, ne • HadronPhysicsLHEP G4 Meson, Barion and ShortLived constructors • MuonPhysics muons and taus • IonPhysics G4IonConstructor, Deuteron, Triton, Alpha, 3He

12. LCDXML2G4DetConst • Detector construction from XML input file • XML parsing is done by Sun’s xercesc library • Limitation: cylinders or disks only • Uses other classes to do the real work: • LCDXML2G4VXD • LCDXML2G4Tracker • LCDXML2G4Lum • LCDXML2G4EMCal • LCDXML2G4HDCal • LCDXML2G4Muon • LCDG4MaterialMgr • LCDXML2G4Field • LCDXML2G4InactiveVolume

13. XML detector description <?xml version="1.0" ?> <!-- SDJan03.xml - Standard Silicon Detector --> <!DOCTYPE lcdparm SYSTEM "detParms.dtd" > <lcdparm> <global file="SDJan03.xml" /> <physical_detector topology="silicon" id = "SDJan03" > <-- Just an example: description of the HCal barrel --> <volume id="HAD_BARREL" rad_len_cm="1.133" inter_len_cm="0.1193"> <tube> <barrel_dimensions inner_r = "144.0" outer_z = "286.0" /> <layering n="34"> <slice material = "Stainless_steel" width = "2.0" /> <slice material = "Polystyrene" width = "1.0" sensitive = "yes“ /> </layering> <segmentation cos_theta = "600" phi = "1200" /> </tube> <calorimeter type = "had" /> </volume> <-- all other volumes dropped... --> </physical_detector> </lcdparm>

14. LCDG4PrimaryGeneratorAction • Inherits from G4VUserPrimaryGeneratorAction • LCDG4readStdFile for binary StdHEP input file • A Geant4 primary track is created for each MC particle in the input file • LCDMcPart keeps track of parents and some additional information (one for each track, except for tracks produced inside a calorimeter shower) • LCDG4Trk2McPart inherits from G4VUserTrackInformation and associates one or more G4Tracks to one LCDMcPart • Standard G4ParticleGun can also be used • LCDG4PrimaryGeneratorMessenger can be used for simple interactive changes to the G4ParticleGun generator

15. LCDG4TrackingAction • Inherits from G4UserTrackingAction • Builds the associations between parents and children, so that all hits can be traced back to a MC particle saved in output file • It does this by creating an LCDG4Trk2McPart object for each secondary particle created by Geant during tracking

16. LCDG4SteppingAction • Inherits from G4UserSteppingAction • It complements LCDG4TrackingAction by creating LCDMcPart objects for non-primary particles (except for particles from calorimeter showers) • It is also used for geantino scans, to calculate accumulated radiation and interaction lengths along straight lines

17. LCDG4EventAction • Accesses all hit collections (G4HCofThisEvent) and streams hits and MC particles into output format • Output formats are LCD-specific (sio and lcio) • Data format keeps links between different objects, like hits associated to MC particles • Some limited ASCII output can be used for debugging purposes

18. Hit Processing • LCDG4HDCalSD inherits from G4VSensitiveDetector • Determines which cell was hit based on the PreStepPoint coordinates (virtual cells!) • LCDG4HDCalHit keeps track of hit information in each individual cell. It inherits from G4VHit • Energy deposition is linked to the MC particle • Energy deposition in absorbers are also kept for analysis • Similar classes exist for each subcomponent

19. Projective vs. Non-projective • An important parameter to be studied at the earlier stages of the design • Mokka doesn’t currently have this functionality Projective Non-projective

20. e+e- → Z → m+m- (SDJan03)

21. e+e- → tt event (SDJan03)

22. e+e- → Z → qq event (SDJan03)

23. Status • Detailed comparisons between LCDG4 and Mokka under way • Only cylinders and disks currently supported • Plans to upgrade from XML to GDML • Other Geant4 projects: • NICADD test stand • Test beam prototype (see Jeremy’s talk!) • For more information, please check: http://nicadd.niu.edu/research/lcd