$Id: README,v 1.8 2003/12/01 19:12:38 perl Exp $
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Geant4 - an Object-Oriented Toolkit for Simulation in HEP
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Extended Example A01
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Example A01 implements a double-arm spectrometer with wire chambers,
hodoscopes and calorimeters. Event simulation and collection are
enabled, as well as event display and analysis. This example is
extensively documented on the Geant4 Workshop Tutorial CD available at:
http://geant4.slac.stanford.edu/g4cd/Welcome.html
1. GEOMETRY
The spectrometer consists of two detector arms. One arm provides
position and timing information of the incident particle while the
other collects position, timing and energy information of the particle
after it has been deflected by a magnetic field centered at the
spectrometer pivot point.
- First arm: box filled with air, also containing:
1 hodoscope (15 vertical strips of plastic scintillator)
1 drift chamber (5 horizontal argon gas layers with a
"virtual wire" at the center of each layer)
- Magnetic field region: air-filled cylinder which contains
the field
- Second arm: box filled with air, also containing:
1 hodoscope (25 vertical strips of plastic scintillator)
1 drift chamber (5 horizontal argon gas layers with a
"virtual wire" at the center of each layer)
1 electromagnetic calorimeter:
a box sub-divided along x,y and z
axes into cells of CsI
1 hadronic calorimeter:
a box sub-divided along x,y, and z axes
into cells of lead, with a layer of
plastic scintillator placed at the center
of each cell
2. PHYSICS
This example uses the following physics processes:
- electromagnetic:
photo-electric effect
Compton scattering
pair production
bremsstrahlung
ionization
multiple scattering
annihilation
- decay
- transportation in a field
and defines the following particles:
geantino, charged geantino, gamma, all leptons,
pions, charged kaons
Note that even though hadrons are defined, no hadronic processes
are invoked in this example.
3. EVENT:
An event consists of the generation of a single particle which is
transported through the first spectrometer arm. Here, a scintillator
hodoscope records the reference time of the particle before it passes
through a drift chamber where the particle position is measured.
Momentum analysis is performed as the particle passes through a magnetic
field at the spectrometer pivot and then into the second spectrometer
arm. In the second arm, the particle passes through another hodoscope
and drift chamber before interacting in the electromagnetic calorimeter.
Here it is likely that particles will induce electromagnetic showers.
The shower energy is recorded in a three-dimensional array of CsI
crystals. Secondary particles from the shower, as well as primary
particles which do not interact in the CsI crystals, pass into the
hadronic calorimeter. Here, the remaining energy is collected in a
three-dimensional array of scintillator-lead sandwiches.
Several aspects of the event may be changed interactively by the user:
- initial particle type
- initial momentum and angle
- momentum and angle spreads
- type of initial particle may be randomized
- strength of magnetic field
- angle of the second spectrometer arm
4. DETECTOR RESPONSE:
All the information required to simulate and analyze an event is
recorded in HITS. This information is recorded in the following
sensitive detectors:
- hodoscope:
particle time
particle position
strip ID
- drift chamber:
particle time
particle position
layer ID
- electromagnetic calorimeter:
particle position
energy deposited in cell
cell ID
- hadronic calorimeter:
particle position
energy deposited in cell
cell ID
5. VISUALIZATION:
Simulated events can be displayed on top of a representation of
the spectrometer.
vis.mac outputs HepRep version 1 files suitable for viewing in WIRED.
Change the /vis/open line from HepRepFile to DAWNFILE to instead
make .prim files suitable for viewing in DAWN.
heprep2-000-gz.mac outputs a series of gzipped HepRep version 2 files
each containing a single event, suitable for viewing in WIRED (there
is no need to ungzip them since WIRED can do this itself).
heprep2zip.mac outputs a single zip file that unzips to a series of
HepRep version 2 files, each each containing a single event (unzip
the single file by hand, then view the resulting individial HepRep
files in WIRED).
heprep2-000-zip.mac outputs a series of zipped HepRep version 2 files
each containing a single event (not yet viewable in WIRED unless you
explicitly unzip them before viewing).
heprep2.mac outputs a HepRep version 2 file with multiple events
appended to a single file in an experimental manner (not yet viewable
in WIRED).
heprep2gz.mac outputs a HepRep version 2 file with multiple events
appended to a single file in an experimental manner (not yet viewable
in WIRED).
For more information on visualization with this A01 example,
see the visualization tutorials on the Geant4 Workshop Tutorial CD
available at:
http://geant4.slac.stanford.edu/g4cd/Welcome.html
6. ANALYSIS:
This example implements an AIDA-compliant analysis system which
creates histograms, ntuples and plotters. At the completion of a
simulation run a file A01.aida is produced which contains these
data structures. This file can be used as an input to the Java
Analysis Studio (JAS) which allows the histograms and ntuples to
examined, manipulated, saved and printed. For further details,
see README.JAIDA.
7. GETTING STARTED:
Build the A01 executable:
cd to A01
gmake clean
gmake
gmake will create tmp and bin directories in your work directory.
The executable, named A01app, will be in /bin/$G4SYSTEM/
While in directory A01, run the executable:
../bin/$G4SYSTEM/A01app
which will bring up the interactive prompt:
Idle>
To run 10 events you can now enter:
/run/beamOn 10
If all goes well, a JAS window will appear containing two histograms
and three scatterplots.
To terminate the job, at the prompt enter:
exit
Currently you must also close the JAS-AIDA window to get the job to stop.
In the A01 directory will be a file A01.aida which contains the plots.
To examine them
/usr/local.bin/jas3 & or jas3 &
Gabriele Cosmo