Detector Simulation

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Detector Simulation
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• How to do HEP experiment
• Particle Accelerator
• Particle Detector
• What is detector simulation?
• GEANT toolkit

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Quiz
Processes in neutron decay exist in which the
conservation of energy and momentum apprears to
be violated, because W boson appears
during an intermediate stage of the process, even
though there isnt enough energy to create
such massive particle. How can we explain it?
DE Dt h/4p (Heigenberg Uncertainty principle)
gt W boson is called a virtual paricle in this
process.
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High Energy Experiment
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Fixed target vs Colliding beams
(total energy)2-(total momentum)2 invariant in
all frames of reference Assume that 800GeV(Ebeam)
proton collides in a fixed target(proton).
Center of mom. frame Laboraroty frame
Total energy ECM
Ebeammp2
Total momentum 0
Pbeam
Invariant
ECM2 (Ebeammp2)2-Pbeam2
E 2(mp2Ebeammp) 1/2 38.8GeV We
are enough to 19.4GeV19.4GeV proton beams in
collider !!!
Question Whats the advantage of a fixed target
experiment?
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Global Sketch of HEP Experiment
Determine Physics Goal
Simulation Study
Beam/Detector
Decide subdetectors
Subdetector RD
Electronics RD
Software RD
Beam test
Readout Trigger(hardware)
Simulation code Trigger(software) Rawdata
recording Data reconstruction Skimming/MDST Analys
is tools Database Caliibration Monitoring
System Integration
Cosmic rays Beam commissioning System debugging
System Calibration
Data Taking
Momentum/Energy/Mass PID/Lifetime/BF Resolution/Ef
ficiency/background Systematic study
Data Analysis
Publish Results
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Particle Accelerator
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Particle Accelerator
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Particle detector
Muons (m)
HAD Cal.
E.M. Cal.
Muon Cham.
Tracker
g
Hadrons (h)
e, g
e
m
Charged Tracks e, m, h
p, p
n
Heavy material, Ironactive material
High Z materials, e.g., lead tungstate crystals
Heavy absorber,(e.g., Fe) Zone where n and m
remain
Lightweight
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Particle Detector

• Interactions of particles and radiation with
  matter
• Ionization and track measurements
• Time measurement
• Particle identification
• Energy measurement
• Momentum measurement
• Particle Detectors, C.Grupen, Cambridge Univ.
  Press, 1996
• Experimental techniques in HEP, T.Ferbel, World
  Scientific, 1991
• http//www.cern.ch/Physics/ParticleDetector/Brief
  Book

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Heavy charged particle interactions w/ atoms
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Stopping power
Heavy charged particles interact with matter
mainly thru electrostatic forces during
collisions with orbiting electrons. (excitation,
ionization)
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g/e interactions w/ atoms
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Time measurement
The scintillation counter is capable of measuring
a precise passing time of a particle because the
scintillation is a fast phenomenum and the
conversion of a light burst into a voltage signal
inside PMT is also a very fast process.
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Particle Identification
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Cherenkov counter
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Tracking detector
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Energy measurement
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Momentum measurement
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Why to do simulation study

• HEP experimental apparatus needs huge expenses.
• Detector optimization is necessary ahead of
  detector construction.
• Simulation library contains all of possible
  physics processes that have been well proven.
• Detector performance can be checked out and
  debugged if any discrepancy is appeared.
• Its possible to see what is happened at detector
  itself, and to shorten a period of time of system
  completion.

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What is detector simulation?

• A detector simulation program must provide the
  possibility of describing accurately an
  experimental setup (both in terms of materials
  and geometry).
• The program must provide the possibility of
  generating physics events(kinematics) and
  efficiently tracking particles through the
  simulated detector.
• The interactions between particles and matter
  must be simulated by taking into account all
  possible physics processes, for the whole energy
  range.
• The possibility of recording at run time all
  quantities needed for reproducing the experiment
  functioning must be provided.
• Some graphic and plot utilities must be in place.
• and much more

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Typical experimental setup
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Fully reconstructed BBbar event
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Event Generator

• Lund Monte Carlo using PYTHIA/JETSET is most
  popular event generator in HEP experiment to
  describe collisions at high energies between
  elementary particles such as e/e-/p/pbar in
  various combinations.
• PYTHIA/JETSETCERN-TH.7112/93 contain
  theory/models for a number of physics aspects,
  including hard/soft interactions, fragmentation
  and decay.
• Usually each experiment has their own event
  generator modified slightly with existing ones to
  accommodate their own purpose.
• Have a look at wwwinfo.cern.ch/asd/cernlib/mc.html
  

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Tracking

• Calculate a set of points in a seven-dimensional
  space(x,y,z,t,Px,Py,Pz) of particle trajectory.
• Key role to measure each track momentum and event
  vertexing with precise vertex detector
• Deviation of a charged particle in a magetic
  field
• Energy loss due to bremsstrahlung
• Energy loss due to ionization
• Deviation from multiple Coulomb scattering
• Deviation from elastic electromagnetic scattering

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All possible physics processes

• Processes by photon
• (e,e-) pair production
• Compton collision
• Photoelectric effect
• Photo fission of heavy elements
• Rayleigh effect
• Processes by e
• Multiple scattering
• Ionization and d-rays production
• Bremsstrahlung
• Annihilation of positron
• Generation of Cerenkov light
• Synchrotron radiation

Processes by hadrons Decay in flight Multiple
scattering Ionization and d-rays
production Hadronic interaction Generation of
Cerenkov light Processes by m Decay in
flight Multiple scattering Ionization and d-rays
production Ionisation by heavy ions Bremsstrahlung
Direct (e,e-) pair production Photonuclear
interaction Generation of Cerenkov light
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Recording

• All readout channels from each subdetector should
  be recorded as real experiment.
• Hit and Digitization information are recorded.
• Simulation package gives more detail information
  to make system debugging possible.
• Reconstruction efficiency (detector acceptance)
  is computed by simulation study.

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Utilities

• HBOOK package for histogramming and fitting
• HIGZ High level Interface to Graphics and ZEBRA
• PAW Physics Analysis Workstation
• ROOT OO Data Analysis Framework
• GEANT Detector Description and Simulation Tool
• EGS Electron-Gamma Simulation package

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GEANT
Detector Description and Simulation Tool

• Detector design and optimisation
• Development and testing of reconstruction and
  analysis programs
• Interpretation of experimental data
• Principal applications to HEP are
• to track particles thru an experimental setup for
  the simulation of detector response
• to graphically represent the experimental setup
  and particle trajectories.
• It has been also used in the areas of medical and
  biological sciences, radioprotection, and
  astronautics.
• http//wwwinfo.cern.ch/asdoc/geant_html3/gean
  tall.html

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GEANT3

• This is a detector simulation program developed
  for the LEP era
• Fortran, ZEBRA
• EM physics directly from EGS
• Hadronic physics added as an afterthought (and
  always by interfacing with external packages)
• Powerful but simplistic geometry model
• Physics processes very often limited to LEP
  energy range(100GeV)
• LHC detectors need powerful simulation tools for
  next 20 years
• Reliability, extensibility, maintainability,
  openness
• Good physics, with the possibilty of extending
• GEANT4 package using C has been prepared.
• http//wwwinfo.cern.ch/asd/geant4/genat4.html

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GEANT3
Introduction to the manual http//wwwinfo.cern.ch/
asd/geant/

• AAAA introduction to the system
• BASE GEANT framework and user interface to be
  read first
• CONS particles, materials and tracking medium
  parameters
• DRAW drawing package, interfaced to HIGZ
• GEOM geometry package
• HITS detector response package
• IOPA I/O package
• KINE event generators and kinematic structures
• PHYS physics processes
• TRAK tracking package
• XINT interactive user interface

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GEANT3 Basics
Interactive vs Batch Execution

• User has two choices of how to run their
  simulation with GEANT3
• Interactive Mode very useful for program
  testing and debugging.
• Batch Mode suitable for generating large number
  of events once the detector design has been
  finalized.
• Switching between modes requires recompling with
  one of two possible PROGRAM MAIN routines.

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GEANT3 Basics
Interactive vs Batch Execution

• PROGRAM MAIN for interactive mode running
• PROGRAM GXINT
• C GEANT main program for interactive running
• C MOTIF user interface routine
  GPAWPP(NWGEAN,NWPAW)
• C X11 user interface routine
  GPAW(NWGEAN,NWPAW)
• PARAMETER (NWGEAN3000000, NWPAW1000000)
• COMMON/GCBANK/GEANT(NWGEAN)
• COMMON/PAWC/PAW(NWPAW)
• CALL GPAW(NWGEAN,NWPAW)
• END

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GEANT3 Basics
Interactive vs Batch Execution

• PROGRAM MAIN for batch mode running
• PROGRAM MAIN_BATCH
• C GEANT main program for batch running
• PARAMETER (NGBANK5000000, NHBOOK1000000)
• COMMON/GCBANK/Q(NGBANK)
• COMMON/PAWC/H(NHBOOK)
• C initialize HBOOK and GEANT memory
• CALL GZEBRA(NGBANK)
• CALL HLIMIT(-NHBOOK)
• C initialize GEANT
• CALL UGINIT
• C start event processing
• CALL GRUN
• C end of run terminate
• CALL UGLAST
• END

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GEANT3 Basics
Program Initialization

• For both interactive and batch mode running, USER
  must initialize with the UGINIT various aspects
  of the GEANT program including
• User FFREAD and HBOOK files UFILES
• GEANT initialization GINIT
• Datacard input GFFGO
• Data structures GZINIT
• Material tables GMATE
• Particle tables GPART
• User define materials UGMATE
• User defined detector geometry UGEOM
• Energy loss and cross section tables GPHYSI
• User histograms UHINIT

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• SUBROUTINE UGINIT
• include include/gckine.inc
• include include/demo.inc
• C
  
• C This subroutine initializes GEANT and USER
  subroutine
• C
  
• CALL UFILES ! open user FFREAD and HBOOK files
• CALL GINIT ! intialize GEANT
• C define user FFREAD data cards and read
• CALL FFKEY(GEOS,GEOS,1,INTEGER) ! UGEOM
  sel. Value
• CALL FFSET(LINP,4)
• CALL GFFGO
• CALL GZINIT ! initailize data structure
• CALL GMATE ! initialize standard materials
• CALL GPART ! initialize particle table
• CALL GPIONS ! initialize ion table
• CALL UGMATE ! define user material tracking
  param.
• CALL UGEOM ! define user geometry
• CALL GPHYSI ! energy loss cross section
  tables

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GEANT3 Detector Descripttion

• Within GEANT the user specifies the detector
  properties in the routines UGMATE and UGEOM
• UGMATE deifne any user materials (GSMIXT) and
  tracking parameters (GSTMED)
• UGEOM define the detector geometry (GSVOLU) and
  position volumes (GSPOS)

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GEANT3 Kinematics

• Within GEANT the kinematics of the processes to
  be simulated are determined by the user in the
  routine GUKINE. Here the user can specify
• Incoming particle type
• Incoming particle origin, momentum (x,y,z)
• These values can be changed without recompling
  through the IKINE and PKINE datacards.

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GEANT3 Visualization

• What is required to take advantage of the display
  capabilties of interactive GEANT?
• Important to correctly add each track to the
  tracking STACK within GUSTEP subroutine by
  setting IFLGK(IG)1
• When running in interactive mode there are a
  variety of options available to best display your
  detector design geometry and particle
  interactions.
• Viewing options are controlled by the GDOPT and
  SATT commands.

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GEANT3 FAQ

• How do I draw my detector in fancy colors? With
  tracks displayed?
• How do I draw a scale on the display? Axis?
• How do I draw a human figure near the detector
  for comparison?
• How do I create a postcript file of the image?
• How can I examine a detector region more closely?
• How can I identify the particle type and momenta
  of interesting tracks?
• How do I view the detector components not in
  wire-frame display? Explode view?
• How can I easily change my viewing perspective
  about the detector?
• How can I have my histograms and Ntuples written
  out to file?