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#README#
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$Id: README 104901 2017-06-26 14:40:57Z gcosmo $
-------------------------------------------------------------------
=========================================================
Geant4 - an Object-Oriented Toolkit for Simulation in HEP
=========================================================
Example B4
-----------
This example simulates a simple Sampling Calorimeter setup.
To demonstrate several possible ways of data scoring, the example
is provided in four variants: B4a, B4b, B4c, B4d.
(See also examples/extended/electromagnetic/TestEm3)
1- GEOMETRY DEFINITION
The geometry is constructed in B4[c,d]DetectorConstruction class.
The calorimeter is a box made of a given number of layers. A layer
consists of an absorber plate and of a detection gap. The layer is
replicated.
Four parameters define the geometry of the calorimeter :
- the thickness of an absorber plate,
- the thickness of a gap,
- the number of layers, and
- the transverse size of the calorimeter (the entrance face is a square).
In addition, a global, uniform, and transverse magnetic field can be
applied using G4GlobalMagFieldMessenger, instantiated in
B4[c,d]DetectorConstruction::ConstructSDandField
with a non zero field value, or via interactive commands.
For example:
/globalField/setValue 0.2 0 0 tesla
|<----layer 0---------->|<----layer 1---------->|<----layer 2---------->|
| | | |
==========================================================================
|| | || | || | ||
|| | || | || | ||
beam || absorber | gap || absorber | gap || absorber | gap ||
======> || | || | || | ||
|| | || | || | ||
==========================================================================
A more general version of this geometry can be found in:
examples/extended/electromagnetic/TestEm3
where all the geometry parameters, the absorber and gap materials
can be modified interactively via the commands defined in the DetectorMessenger
class.
2- PHYSICS LIST
The particle's type and the physic processes which will be available
in this example are set in the FTFP_BERT physics list. This physics list
requires data files for electromagnetic and hadronic processes.
See more on installation of the datasets in Geant4 Installation Guide,
Chapter 3.3: Note On Geant4 Datasets:
http://geant4.web.cern.ch/geant4/UserDocumentation/UsersGuides/InstallationGuide/html/ch03s03.html
The following datasets: G4LEDATA, G4LEVELGAMMADATA, G4SAIDXSDATA and
G4ENSDFSTATEDATA are mandatory for this example.
In addition the build-in interactive command:
/process/(in)activate processName
allows to activate/inactivate the processes one by one.
3- ACTION INITALIZATION
A newly introduced class, B4[a,b,c,d]ActionInitialization,
instantiates and registers to Geant4 kernel all user action classes.
While in sequential mode the action classes are instatiated just once,
via invoking the method:
B4[a,b,c,d]ActionInitialization::Build()
in multi-threading mode the same method is invoked for each thread worker
and so all user action classes are defined thread-local.
A run action class is instantiated both thread-local
and global that's why its instance is created also in the method
B4[a,b,c,d]ActionInitialization::BuildForMaster()
which is invoked only in multi-threading mode.
4- PRIMARY GENERATOR
The primary beam consists of a single particle which hits the
calorimeter perpendicular to the input face. The type of the particle
and its energy are set in the B4PrimaryGeneratorAction class, and can
be changed via the G4 built-in commands of the G4ParticleGun class (see
the macros provided with this example).
5- RUNS and EVENTS
A run is a set of events.
The user can choose the frequency of printing via the Geant4 interactive
command, for example:
/run/printProgress 100
6- DETECTOR RESPONSE
The energy deposit and track lengths of the charged particles are recorded on
an event by event basis in the Absober and Gap layers.
In order to demonstrate several possible ways of data scoring,
the example is provided in four variants:
Variant a: User Actions
These 4 quantities are data members of the B4aEventAction class.
They are collected step by step in
B4aSteppingAction::UserSteppingAction(), and passed to the event action
via two methods: B4aEventAction::AddAbs() and B4aEventAction::AddGap().
In B4aEventAction::EndOfEventAction(), these quantities are printed and
filled in H1D histograms and ntuple to accumulate statistic and compute
dispersion.
Variant b: User data object
In order to avoid dependencies between action classes, a user object
B4bRunData, derived from G4Run, is defined with data members needed
for the accounted information.
In order to reduce the number of data members a 2-dimensions array
is introduced for each quantity.
Then the quantities are collected step by step in user action classes:
B4bSteppingAction::UserSteppingAction() and
B4bEventAction::EndOfEventAction() in a similar way as in variant a.
Variant c: Hits and Sensitive detectors
In this option, the physics quantities are accounted using the hits
and sensitive detectors framework defined in the Geant4 kernel.
The physics quantities are stored in B4cCalorHit via two B4cCalorimeterSD
objects, one associated with the Absorber volume and another one with Gap
in B4cDetectorConstruction::ConstructSDandField().
In contrary to the B2 example (Tracker) where a new hit is created
with each track passing the sensitive volume (in the calorimeter), only one
hit is created for each calorimeter layer and one more hit to account for
the total quantities in all layers. In addition to the variants a and b,
the quantities per each layer are also available in addition to the total
quantities.
Variant d: Scorer
In this option, the Geant4 scorers which are defined on the top of hits
and sensitive detectors Geant4 framework are used.
In practice this means that the user does not need to define hits and sensitive
detector classes but rather uses the classes already defined
in Geant4. In this example, the G4MultiFunctionalDetector with
G4PSEnergyDeposit and G4PSTrackLength primitive scores are used (see
B4dDetectorConstruction::ConstructSDandField()).
Also with this approach, the quantities per each layer are available
in addition to the total quantities.
7- HISTOGRAMS
The analysis tools are used to accumulate statistics and compute the dispersion
of the energy deposit and track lengths of the charged particles.
H1D histograms are created in B4[b]RunAction::B4[b]RunAction() for the
following quantities:
- Energy deposit in absorber
- Energy deposit in gap
- Track length in absorber
- Track length in gap
The same values are also saved in an ntuple.
The histograms and the ntuple are saved in the output file in a format
according to a technology selected in B4Analysis.hh, the default in this example
is ROOT.
The accumulated statistic and computed dispersion is printed at the end of
run, in B4RunAction::EndOfRunAction().
When running in multi-threading mode, the histograms and the ntuple accumulated
on threads are merged in a single output file. While merging of histograms is
performed by default, merging of ntuples is explicitly activated in the B4RunAction
constructor.
The ROOT histograms and ntuple can be plotted with ROOT using the plotHisto.C
and plotNtuple.C macros.
8- VISUALIZATION TUTORIAL
Additional visualization tutorial macros are available in the visTutor
subdirectory. They can be tried as:
% cd B4/B4[a,b,c,d]
% ln -s ../macros/visTutor visTutor
% exampleB4[a,b,c,d]
Idle > /control/execute visTutor/exN03VisX.mac
For details, see comment lines described in the macro files.
These macros are designed to help your understanding of the User's Guide.
9- HOW TO RUN
This example handles the program arguments in a new way.
It can be run with the following optional arguments:
% exampleB4a [-m macro ] [-u UIsession] [-t nThreads]
The -t option is available only in multi-threading mode
and it allows the user to override the Geant4 default number of
threads. The number of threads can be also set via G4FORCENUMBEROFTHREADS
environment variable which has the top priority.
- Execute exampleB4a in the 'interactive mode' with visualization
% exampleB4a
and type in the commands from run1.mac line by line:
Idle> /tracking/verbose 1
Idle> /run/beamOn 1
Idle> ...
Idle> exit
or
Idle> /control/execute run1.mac
....
Idle> exit
- Execute exampleB4a in the 'batch' mode from macro files
(without visualization)
% exampleB4a -m run2.mac
% exampleB4a -m exampleB4.in > exampleB4.out
- Execute exampleB4a in the 'interactive mode' with a selected UI session,
e.g. tcsh
% exampleB4a -u tcsh
The following paragraphs are common to all basic examples
A- VISUALIZATION
The visualization manager is set via the G4VisExecutive class
in the main() function in exampleB4a.cc.
The initialisation of the drawing is done via a set of /vis/ commands
in the macro vis.mac. This macro is automatically read from
the main function when the example is used in interactive running mode.
By default, vis.mac opens an OpenGL viewer (/vis/open OGL).
The user can change the initial viewer by commenting out this line
and instead uncommenting one of the other /vis/open statements, such as
HepRepFile or DAWNFILE (which produce files that can be viewed with the
HepRApp and DAWN viewers, respectively). Note that one can always
open new viewers at any time from the command line. For example, if
you already have a view in, say, an OpenGL window with a name
"viewer-0", then
/vis/open DAWNFILE
then to get the same view
/vis/viewer/copyView viewer-0
or to get the same view *plus* scene-modifications
/vis/viewer/set/all viewer-0
then to see the result
/vis/viewer/flush
The DAWNFILE, HepRepFile drivers are always available
(since they require no external libraries), but the OGL driver requires
that the Geant4 libraries have been built with the OpenGL option.
For more information on visualization, including information on how to
install and run DAWN, OpenGL and HepRApp, see the visualization tutorials,
for example,
http://geant4.slac.stanford.edu/Presentations/vis/G4[VIS]Tutorial/G4[VIS]Tutorial.html
(where [VIS] can be replaced by DAWN, OpenGL and HepRApp)
The tracks are automatically drawn at the end of each event, accumulated
for all events and erased at the beginning of the next run.
B- USER INTERFACES
The user command interface is set via the G4UIExecutive class
in the main() function in exampleB4a.cc
The selection of the user command interface is then done automatically
according to the Geant4 configuration or it can be done explicitly via
the third argument of the G4UIExecutive constructor (see exampleB4a.cc).