Gabriele Cosmo
121 lines
4.3 KiB
Plaintext
121 lines
4.3 KiB
Plaintext
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------------------------------------------------------------
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Example of the external decayer implementation with Pythia8
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------------------------------------------------------------
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This example demonstrates how to outfit Pythia8-based decay features
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to those resonances in Geant4 where decay tables are not implemented
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by default. In addition, it showns how to replace existing
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Geant4 decay tables to such resonances as tau+/- or B+/- with
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the Pythia8-based ones.
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This example is activated by setting up PYTHIA8 environment variable
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to point to the area where Pythia8 is installed.
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The complete Pythia8 information, including on download, and documentation
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is available from the following site:
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https://pythia.org
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The original version of this example has been implemented by Julia Yarba
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(FNAL, USA)
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For the complete list of the classes that compose this example please
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see later in this document.
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Location of example:
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examples/extended/eventgenerator/pythia/py8decayer
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Installation of Pythia8:
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NOTE: As of June 2021, pythia8.3.0.5 is the most current version,
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this it is used in this example.
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In the future, please check updates at Pythi8 site: https://pythia.org
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1. cd path/to/your/pythia8/area
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2. Download desired version of Pythia8 and un-tar it, e.g.
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wget http://home.thep.lu.se/~torbjorn/pythia8/pythia8305.tgz
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tar xzf pythia8305.tgz
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3. Build/install Pythia8
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cd pythia8305
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export CXX=\`which g++\`
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./configure --prefix=$PWD --cxx=$CXX
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make
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NOTE: By default, Pythia8 (as of 8.3.0.5) builds with C++11 standards.
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If one wants to turn to e.g. C++17 standard, one needs to override flags
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via --cxx-common argument to configure script.
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4. Setup PYTHIA8 environment variable to point to the area where Pythia8
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is built/installed:
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export PYTHIA8=$PWD
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Building example:
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Upon setup of PYTHIA8 environment variable to point to the area where
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Pythia8 package is installed, the pythia/py8decayer example will be
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compiled together with several other features of the eventgenerator example.
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Description of classes:
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Py8Decayer class provides implementation of the G4VExternalDecayer interface
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with the use of PYTHIA8.
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It is reasonably annotated, and demonstrates what features of Pythia8 need
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to be activated and/or disactivated in order to make Pythia8 work only in
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the decay mode.
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It also illustrated how to control several other features of Pythia8, including
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some reduction of Pythia8 verbosity (by default, Pythia8 produces quite a large
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amount of printouts, thus reducing it could be useful in some cases).
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Last but not least, it also shown how to deactivate decays of pi0's by Pythia8
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as the idea is to handle pi0's back to Geant4 for decays.
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Py8DecayerPhysics class implements a G4VPhysicsConstructor type of component
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with the use of Py8Decayer; this component can later be used with a ddsired
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physics list (see main program).
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Specifically, in the Py8DecayerPhysics::ConstructProcess() the Py8Decayer is
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instantiated and is used to
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a) replace existing decay tables of such resonances as tau+/- and B+/-
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b) supplement decay features to those resonances in Geant4 where the decay
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tables are not implemnted by defaukt
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In principle, classes Py8Decayer and Py8DecayerPhysics can be directly reused with
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another user application.
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Alternatively, they can be used as an inspiration to implement similar, or perhaps
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even more extensive Pythia8-based functionalities of user's choice.
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Class DetConstruction demostrates how to implement minimalistic detector geometry.
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Class SingleParticleGun demonstrates how to implement generaton of the primary
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particle.
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Main program:
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pythia8_decayer.cc
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Executable:
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pythia8_decayer
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Execution:
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At present, the pythia8_decayer executable does not take any input arguments.
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Everything, including the choine of primary particle, is hardcoded in the main.
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Although in the future some configurability may be added.
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By default it'll run 5 single tau events using Pythia8 to decays them.
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It should print some Pythia8 event information, including on decays.
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Once again, please bear in mind that the decay of pi0's by Pythia8 is disabled
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(see Py8Decayer constructor) since the idea is to hand the pi0's back to Geant4
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and make Geant4 decay them.
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