Gabriele Cosmo
166 lines
6.2 KiB
Plaintext
166 lines
6.2 KiB
Plaintext
$Id: README,v 1.10 2009-11-21 00:22:55 perl Exp $
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Geant4 - an Object-Oriented Toolkit for Simulation in HEP
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=========================================================
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Extended Example A01
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--------------------
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Example A01 implements a double-arm spectrometer with wire chambers,
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hodoscopes and calorimeters. Event simulation and collection are
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enabled, as well as event display and analysis.
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1. GEOMETRY
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The spectrometer consists of two detector arms. One arm provides
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position and timing information of the incident particle while the
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other collects position, timing and energy information of the particle
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after it has been deflected by a magnetic field centered at the
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spectrometer pivot point.
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- First arm: box filled with air, also containing:
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1 hodoscope (15 vertical strips of plastic scintillator)
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1 drift chamber (5 horizontal argon gas layers with a
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"virtual wire" at the center of each layer)
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- Magnetic field region: air-filled cylinder which contains
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the field
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- Second arm: box filled with air, also containing:
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1 hodoscope (25 vertical strips of plastic scintillator)
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1 drift chamber (5 horizontal argon gas layers with a
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"virtual wire" at the center of each layer)
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1 electromagnetic calorimeter:
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a box sub-divided along x,y and z
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axes into cells of CsI
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1 hadronic calorimeter:
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a box sub-divided along x,y, and z axes
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into cells of lead, with a layer of
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plastic scintillator placed at the center
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of each cell
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2. PHYSICS
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This example uses the following physics processes:
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- electromagnetic:
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photo-electric effect
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Compton scattering
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pair production
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bremsstrahlung
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ionization
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multiple scattering
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annihilation
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- decay
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- transportation in a field
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and defines the following particles:
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geantino, charged geantino, gamma, all leptons,
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pions, charged kaons
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Note that even though hadrons are defined, no hadronic processes
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are invoked in this example.
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3. EVENT:
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An event consists of the generation of a single particle which is
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transported through the first spectrometer arm. Here, a scintillator
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hodoscope records the reference time of the particle before it passes
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through a drift chamber where the particle position is measured.
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Momentum analysis is performed as the particle passes through a magnetic
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field at the spectrometer pivot and then into the second spectrometer
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arm. In the second arm, the particle passes through another hodoscope
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and drift chamber before interacting in the electromagnetic calorimeter.
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Here it is likely that particles will induce electromagnetic showers.
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The shower energy is recorded in a three-dimensional array of CsI
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crystals. Secondary particles from the shower, as well as primary
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particles which do not interact in the CsI crystals, pass into the
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hadronic calorimeter. Here, the remaining energy is collected in a
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three-dimensional array of scintillator-lead sandwiches.
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Several aspects of the event may be changed interactively by the user:
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- initial particle type
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- initial momentum and angle
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- momentum and angle spreads
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- type of initial particle may be randomized
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- strength of magnetic field
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- angle of the second spectrometer arm
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4. DETECTOR RESPONSE:
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All the information required to simulate and analyze an event is
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recorded in HITS. This information is recorded in the following
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sensitive detectors:
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- hodoscope:
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particle time
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particle position
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strip ID
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- drift chamber:
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particle time
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particle position
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layer ID
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- electromagnetic calorimeter:
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particle position
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energy deposited in cell
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cell ID
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- hadronic calorimeter:
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particle position
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energy deposited in cell
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cell ID
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5. VISUALIZATION:
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Simulated events can be displayed on top of a representation of the spectrometer.
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vis.mac outputs HepRep version 1 files suitable for viewing in HepRApp or WIRED4.
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Change the /vis/open line from HepRepFile to DAWNFILE to instead
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make .prim files suitable for viewing in DAWN.
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heprep2-000-gz.mac outputs a series of gzipped HepRep version 2 files
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each containing a single event, suitable for viewing in HepRApp or WIRED4
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heprep2zip.mac outputs a single zip file that unzips to a series of
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HepRep version 2 files, each each containing a single event (unzip
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the single file by hand, then view the resulting individial HepRep files).
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heprep2-000-zip.mac outputs a series of zipped HepRep version 2 files
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each containing a single event (not yet viewable unless you
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explicitly unzip them before viewing).
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heprep2.mac outputs a HepRep version 2 file with multiple events
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appended to a single file in an experimental manner
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heprep2gz.mac outputs a HepRep version 2 file with multiple events
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appended to a single file in an experimental manner
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Any of the heprep mac files above with the name bheprep (for instance
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bheprep2zip.mac) will write a Binary HepRep version 2 file, readable only
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by WIRED4 (not by HepRApp).
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6. ANALYSIS:
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This example implements an AIDA-compliant analysis system which
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creates histograms, ntuples and plotters. If you have built Geant4 with
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the option to use analysis (answering yes to the appropriate question in
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./Configure -build), then at the completion of a simulation run,
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a file A01.aida is produced which contains these data structures.
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This file can be used as an input to the Java Analysis Studio (JAS) which allows
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the histograms and ntuples to examined, manipulated, saved and printed.
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For further details, see also README.AIDA.
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