LCDG4: a Geant4-based detector simulator for the LCD

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LCDG4 a Geant4-based detector simulator
for the LCD

• Guilherme Lima
• for the NICADD simulations group

Geant4 Tutorial Fermilab, Oct.28 2003
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Outline

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

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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

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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

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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

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Options under study SD, LD, PD
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A Digital Hadronic Calorimeter?
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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

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Detector Simulation

• Support the detector design activities at NICADD
• Standard 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

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Geant4 implementation

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

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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, Baryon and Short-Lived constructors
• MuonPhysics
• muons and taus
• IonPhysics
• G4IonConstructor, Deuteron, Triton, Alpha, 3He

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LCDXML2G4DetConst

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

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XML detector description
lt?xml version"1.0" ?gt lt!-- SDJan03.xml -
Standard Silicon Detector --gt lt!DOCTYPE lcdparm
SYSTEM "detParms.dtd" gt ltlcdparmgt ltglobal
file"SDJan03.xml" /gt ltphysical_detector
topology"silicon" id "SDJan03" gt lt-- Just
an example description of the HCal barrel --gt
ltvolume id"HAD_BARREL" rad_len_cm"1.133"
inter_len_cm"0.1193"gt lttubegt
ltbarrel_dimensions inner_r "144.0" outer_z
"286.0" /gt ltlayering n"34"gt
ltslice material "Stainless_steel" width "2.0"
/gt ltslice material "Polystyrene"
width "1.0" sensitive "yes /gt
lt/layeringgt ltsegmentation cos_theta
"600" phi "1200" /gt lt/tubegt
ltcalorimeter type "had" /gt lt/volumegt
lt-- all other volumes dropped... --gt
lt/physical_detectorgt lt/lcdparmgt
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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 G4VUserTrackInformat
  ion 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

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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

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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

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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

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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

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Projective vs. Non-projective

• An important parameter to be studied at the
  earlier stages of the design

Projective
Non-projective
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ee- ? Z ? mm- (SDJan03)
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ee- ? tt event (SDJan03)
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ee- ? Z ? qq event (SDJan03)
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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 Jeremys talk!)
• For more information, please check
  http//nicadd.niu.edu/research/lcd