Gabriele Cosmo
236 lines
9.4 KiB
Plaintext
236 lines
9.4 KiB
Plaintext
$Id$
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-------------------------------------------------------------------
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=========================================================
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Geant4 - an Object-Oriented Toolkit for Simulation in HEP
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=========================================================
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Example B4
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-----------
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This example simulates a simple Sampling Calorimeter setup.
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To demonstrate several possible ways of data scoring, the example
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is provided in four variants: B4a, B4b, B4c, B4d.
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(See also examples/extended/electromagnetic/TestEm3)
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1- GEOMETRY DEFINITION
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The calorimeter is a box made of a given number of layers. A layer
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consists of an absorber plate and of a detection gap. The layer is
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replicated.
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Four parameters define the geometry of the calorimeter :
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- the thickness of an absorber plate,
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- the thickness of a gap,
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- the number of layers, and
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- the transverse size of the calorimeter (the entrance face is a square).
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In addition a transverse uniform magnetic field can be applied (see
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B4DetectorMessenger class) and set via the interactive command.
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For example:
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/B4/det/setMagField 0.2 tesla
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|<----layer 0---------->|<----layer 1---------->|<----layer 2---------->|
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==========================================================================
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beam || absorber | gap || absorber | gap || absorber | gap ||
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======> || | || | || | ||
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|| | || | || | ||
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==========================================================================
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A more general version of this geometry can be found in:
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examples/extended/electromagnetic/TestEm3
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where all the geometry parameters, the absorber and gap materials
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can be modified interactively via the commands defined in the DetectorMessenger
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class.
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2- PHYSICS LIST
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The particle's type and the physic processes which will be available
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in this example are set in the FTFP_BERT physics list. This physics
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list requires data files for low energy electromagnetic processes which
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path is defined via the G4LEDATA envirnoment variable.
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In addition the build-in interactive command:
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/process/(in)activate processName
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allows to activate/inactivate the processes one by one.
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3- PRIMARY GENERATOR
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The primary beam consists of a single particle which hits the
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calorimeter perpendicular to the input face. The type of the particle
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and its energy are set in the B4PrimaryGeneratorAction class, and can
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be changed via the G4 build-in commands of the G4ParticleGun class (see
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the macros provided with this example).
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4- RUNS and EVENTS
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A run is a set of events.
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The user can choose the frequency of printing from B4aEventAction (or event
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action classes in other options) via the interactive command defined in
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B4aEventActionMessenger (or messengers classes in other options), for
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example:
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/B4/event/setPrintModulo 100
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5- DETECTOR RESPONSE
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The energy deposit and track lengths of the charged particles are recorded on
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an event by event basis in the Absober and Gap layers.
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In order to demonstrate several possible ways of data scoring,
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the example is provided in four variants:
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Variant a: User Actions
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These 4 quantities are data members of the B4aEventAction class.
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They are collected step by step in
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B4aSteppingAction::UserSteppingAction(), and passed to the event action
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via two methods: B4aEventAction::AddAbs() and B4aEventAction::AddGap().
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In B4aEventAction::EndOfEventAction(), these quantities are printed and
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filled in H1D histograms and ntuple to accumulate statistic and compute
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dispersion.
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Variant b: User data object
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In order to avoid dependencies between action classes, a user object
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B4bRunData is defined with data members needed to the accounted
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information.
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In order to reduce the number of data members a 2-dimensions array
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is introduced for each quantity.
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Then the quantities are collected step by step in user action classes:
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B4bSteppingAction::UserSteppingAction() and
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B4bEventAction::EndOfEventAction() in a similar way as in variant a.
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Variant c: Hits and Sensitive detectors
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In this option, the physics quantities are accounted using the hits
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and sensitive detectors framework defined in the Geant4 kernel.
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The physics quantities are stored in B4cCalorHit via two B4cCalorimeterSD
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objects, one associated with the Absorber volume and another one with Gap
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in B4cDetectorConstruction.
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In contrary to the B2 example (Tracker) where a new hit is created
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with each track passing the sensitive volume (in the calorimeter), only one
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hit is created for each calorimeter layer and one more hit to account for
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the total quantities in all layers. In addition to the variants a and b,
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the quantities per each layer are also available in addition to the total
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quantities.
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Variant d: Scorer
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In this option, the Geant4 scorers which are defined on the top of hits
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and sensitive detectors Geant4 framework are used.
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In practice this means that the user does not need to define hits and sensitive
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detector classes but rather uses the classes already defined
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in Geant4. In this example, the G4MultiFunctionalDetector with
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G4PSEnergyDeposit and G4PSTrackLength primitive scores are used (see
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B4dDetectorConstruction class).
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Also with this approach, the quantities per each layer are available
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in addition to the total quantities.
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6- HISTOGRAMS
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The analysis tools are used to accumulate statistics and compute the dispersion
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of the energy deposit and track lengths of the charged particles.
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H1D histograms are created in B4RunAction::BeginOfRunAction() for the
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following quantities:
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- Energy deposit in absorber
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- Energy deposit in gap
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- Track length in absorber
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- Track length in gap
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The same values are also saved in an ntuple.
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The accumulated statistic and computed dispersion is printed at the end of
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run, in B4RunAction::EndOfRunAction().
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The histograms and ntuple are saved in the output file in a format
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according to a technology selected in B4Analysis.hh.
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7- VISUALIZATION TUTORIAL
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Additional visualization tutorial macros are available in the visTutor
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subdirectory. They can be tried as:
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% cd B4/B4[a,b,c,d]
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% ln -s ../macros/visTutor visTutor
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% exampleB4[a,b,c,d]
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Idle > /control/execute visTutor/exN03VisX.mac
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For details, see comment lines described in the macro files.
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These macros are designed to help your understanding of the User's Guide.
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The following paragraphs are common to all basic examples
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A- VISUALIZATION
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The visualization manager is set via the G4VisExecutive class
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in the main() function in exampleB4a.cc (or in b, c, d variants).
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The initialisation of the drawing is done via a set of /vis/ commands
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in the macro vis.mac. This macro is automatically read from
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the main function when the example is used in interactive running mode.
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By default, vis.mac opens an OpenGL viewer.
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The user can switch to other graphics systems by commenting out this line
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and instead uncommenting one of the other /vis/open statements, such as
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HepRepFile or DAWNFILE (which produce files that can be viewed with the
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HepRApp and DAWN viewers, respectively).
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The DAWNFILE, HepRepFile drivers are always available
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(since they require no external libraries), but the OGL driver requires:
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1- the visualisation & interfaces categories have been compiled
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with the environment variable G4VIS_BUILD_OPENGLX_DRIVER.
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2- exampleB4a.cc has been compiled with G4VIS_USE_OPENGLX.
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(This is best done through Configure or CMake.)
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For more information on visualization, including information on how to
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install and run DAWN, OpenGL and HepRApp, see the visualization tutorials,
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for example,
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http://geant4.slac.stanford.edu/Presentations/vis/G4[VIS]Tutorial/G4[VIS]Tutorial.html
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(where [VIS] can be replaced by DAWN, OpenGL and HepRApp)
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The tracks are automatically drawn at the end of each event, accumulated
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for all events and erased at the beginning of the next run.
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B- USER INTERFACES
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The user command interface is set via the G4UIExecutive class
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in the the main() function in exampleB4a.cc
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The selection of the user command interface is then done automatically
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according to the Geant4 configuration. The default command interface,
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called G4UIterminal, is done via a standard G4cin/G4cout.
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On Linux and Sun-cc one can use a smarter command interface G4UItcsh.
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It is enough to set the environment variable G4UI_USE_TCSH before compiling
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exampleB4a.cc
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C- HOW TO RUN
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- compile and link to generate an executable
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% cd B4/B4a
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% make
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- execute exampleB4a in the 'interactive mode' with visualization
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% exampleB4a
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and type in the commands from run1.mac line by line:
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Idle> /tracking/verbose 1
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Idle> /run/beamOn 1
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Idle> ...
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Idle> exit
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or
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Idle> /control/execute run1.mac
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....
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Idle> exit
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- execute exampleB4a in the 'batch' mode from macro files
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(without visualization)
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% exampleB4a run2.mac
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% exampleB4a exampleB4.in > exampleB4.out
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