Import Geant4 11.4.0 source tree
This commit is contained in:
Gabriele Cosmo
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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 May 2025, pythia8.3.15 is the most current version,
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thus it is used in this example.
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In general, this example is expected to work with any reasonably modern
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pythia8.x.y revision.
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In the future, please check updates at Pythia8 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 https://pythia.org/download/pythia83/pythia8315.tgz
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tar xzf pythia8315.tgz
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3. Build/install Pythia8
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cd pythia8315
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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 8.3.15) builds with C++11 standards.
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If one wants to turn to e.g., C++17 standard (or later), one needs
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to override flags via --cxx-common argument to configure script.
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Alternatively, one can setup CXX_COMMON environment variable.
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As of pythia8315, the default flags are the following:
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-O2 -std=c++11 -pedantic -W -Wall -Wshadow -fPIC -pthread
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Please note use of -pthread which was not among default flags in earlier
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releases of Pythia8.
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Example of specifying C++17 standards by overriding the default flags via
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use of --cxx_common argument to configure script:
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./configure --prefix=$PWD --cxx=$CXX \
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--cxx-common='-O2 -std=c++17 -pedantic -W -Wall -Wshadow -fPIC -pthread'
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4. Setup Pythia8_ROOT environment variable to point to the area where Pythia8
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is built/installed:
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export Pythia8_ROOT=$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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It also shown how to deactivate decays of pi0's by Pythia8 as the idea is to handle
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pi0's back to Geant4 for decays.
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Last but not least, it shows how to outfit Pythia8 with a custom random engine,
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i.e. Py8DecayerEngine.
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Py8DecayerEngine class inherits from Pythia8::RndmEngine which in its turns is
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provided by the Pythia8 package in order to allow replacing the generator's native
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random engine with the one of user's choice.
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In this specific case Py8DecayerEngine allows to replace Pythia8 native random engine
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with the same engine that Geant4 uses (i.e. CLHEP::RanecuEngine as in this application).
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The feature is important for running the example in the MT/Tasking mode.
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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, Py8DecayerEngine, and Py8DecayerPhysics can be
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directly reused with 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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Class ActionInitialization instantiates and registers to Geant4 kernel all user
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action classes; in this case it is SingleParticleGun.
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Main program:
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pythia8_decayer.cc
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This application currently uses the default RunManager which is Tasking and is
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initialized with 5 threads.
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It will then run 5 events, one per thread.
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SerialOnly RunManager can also be employed should the user choose so.
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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.
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Although in the future some configurability may be added.
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As mentioned earlier, it will 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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Additional notes on the contents of Geant4 and Pythia8 Particle Data Tables (PDT) :
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In their default form, PDT's in Geant4 and Pythia8 have a number of differences
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that need to be kept in mind.
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In the case of the Geant4 py8decayer example those differences are unlikely
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to cause any major issues.
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But Pythia8 can, in principle, be used within Geant4 in more ways that just
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as an external decayer.
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Thus, if one is potentially interested in more sophisticated use of Pythia8
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in Geant4, one may want to consider whatever differences exist between (default)
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Geant4 and Pythia8 PDT's.
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Both Geant4 and Pythia8 codes are evolving, and specific numbers may be different
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in earlier and/or in future releases.
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To be more precise, by default Pythia8.3.10 PDT contains 677 entries, of which
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531 particles have an antiparticle (it looks like antiparticles do not make
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separate entries in Pythia8 PDT, but the total number of available species
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should be considered as 1208).
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Geant4 PDT contains 508 entries.
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Of those, 239 particles/antiparticles match by Particle ID's (on the Geant4 side
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it is explicitly called "PDG encoding" while on Pythia8 side it is just "id").
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Many of Pythia8 PDT's entries are not available in Geant4 PDT, e.g. Z or W bosons
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are not in Geant4.
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Some of the species in the Geant4 PDT do not seem to be in the Pythia8 PDT
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(e.g. excited nucleons do not seem to be in the Pythia8 PDT).
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Also, there are entries in both PDT's that mean the same particles but are
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marked with different ID's.
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For example, excited Delta(s) are present in both PDT's but in Geant4 each one
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is marked with a 4-digit number as an ID (PDG encoding) while in Pythia8 an ID
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for such particle would be a 6-digit number starting with "20" and the last
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4 digits would be the same as the Geant4 ID for such particle.
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Speaking of the particles that match by ID (PDG ID), there may be further differences,
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e.g. by mass, either central value or width, or both (there might be other aspects but
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they have not been checked for).
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Starting October 2022, checks have been made from time to time for differences
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larger that 1 keV in either mass central value or width.
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The largest differences have been observed for quarks/diquarks.
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It appears that Geant4 sets (at least) masses of quarks as listed in PDG.
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For details on default settings for the quark masses in Pythia8 please refer
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to the Pythia8 manual:
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https://pythia.org/manuals/pythia8315/Welcome.html
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See Particles and Decays section, Particle Data subsection.
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Beyond quarks/diquarks some differences in mass central values or width have also
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been observed, mainly for resonances.
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But even for such particles as proton or muon there may be differences on the order
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of a few keV (e.g. central value of the proton mass is 938.27 MeV in Pythia8 and
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938.272 MeV in Geant4)
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+21
-25
@@ -1,8 +1,4 @@
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///\file "eventgenerator/pythia/py8decayer/.README.txt"
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///\brief Example py8decayer page
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/*! \page Examplepy8decayer Example py8decayer
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\page Examplepy8decayer Example py8decayer
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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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@@ -35,46 +31,48 @@
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pythia8.x.y revision.
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In the future, please check updates at Pythia8 site: https://pythia.org
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- 1. cd path/to/your/pythia8/area
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- 1.
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```
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cd path/to/your/pythia8/area
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```
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- 2. Download desired version of Pythia8 and un-tar it, e.g.
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\verbatim
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```
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wget https://pythia.org/download/pythia83/pythia8315.tgz
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tar xzf pythia8315.tgz
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\endverbatim
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```
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- 3. Build/install Pythia8
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\verbatim
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```
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cd pythia8315
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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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\endverbatim
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```
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NOTE: By default, Pythia8 (as of 8.3.15) 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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Alternatively, one can setup CXX_COMMON environment variable.
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via `--cxx-common` argument to configure script.
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Alternatively, one can setup `CXX_COMMON` environment variable.
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As of pythia8310, the default flags are the following:
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-O2 -std=c++11 -pedantic -W -Wall -Wshadow -fPIC -pthread
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Please note use of -pthread which was not among default flags in earlier
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`-O2 -std=c++11 -pedantic -W -Wall -Wshadow -fPIC -pthread`. \n
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Please note use of `-pthread` which was not among default flags in earlier
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releases of Pythia8.
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Example of specifying C++17 standards by overriding the default flags via
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use of --cxx_common argument to configure script:
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\verbatim
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use of `--cxx_common` argument to configure script:
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```
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./configure --prefix=$PWD --cxx=$CXX \
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--cxx-common='-O2 -std=c++17 -pedantic -W -Wall -Wshadow -fPIC -pthread'
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\endverbatim
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```
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- 4. Setup Pythia8_ROOT environment variable to point to the area where Pythia8
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is built/installed:
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\verbatim
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```
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export Pythia8_ROOT=$PWD
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\endverbatim
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```
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## Building example:
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Upon setup of Pythia8_ROOT environment variable to point to the area where
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Upon setup of `Pythia8_ROOT` 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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@@ -137,12 +135,12 @@ export Pythia8_ROOT=$PWD
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## Executable:
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pythia8_decayer
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`pythia8_decayer`
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## Execution:
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At present, the pythia8_decayer executable does not take any input arguments.
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At present, the `pythia8_decayer` executable does not take any input arguments.
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Everything, including the choine of primary particle, is hardcoded.
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Although in the future some configurability may be added.
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@@ -214,5 +212,3 @@ export Pythia8_ROOT=$PWD
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of a few keV (e.g. central value of the proton mass is 938.27 MeV in Pythia8 and
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938.272 MeV in Geant4)
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*/
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@@ -23,8 +23,7 @@
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// * acceptance of all terms of the Geant4 Software license. *
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// ********************************************************************
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//
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//
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/// \file eventgenerator/pythia/pythia8decayer/include/ActionInitialization.hh
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/// \file ActionInitialization.hh
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/// \brief Definition of the ActionInitialization class
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#ifndef ActionInitialization_H
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@@ -23,12 +23,10 @@
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// * acceptance of all terms of the Geant4 Software license. *
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// ********************************************************************
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//
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//
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/// \file DetConstruction.hh
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/// \brief Definition of the DetConstruction class
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///
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/// \author J. Yarba; FNAL
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///
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#ifndef DetConstruction_H
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#define DetConstruction_H
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@@ -23,12 +23,10 @@
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// * acceptance of all terms of the Geant4 Software license. *
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// ********************************************************************
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//
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//
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/// \file eventgenerator/pythia/pythia8decayer/include/Py8Decayer.hh
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/// \file Py8Decayer.hh
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/// \brief Definition of the Py8Decayer class
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///
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/// \author J. Yarba; FNAL
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///
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#ifndef Py8Decayer_H
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#define Py8Decayer_H
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@@ -23,12 +23,10 @@
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// * acceptance of all terms of the Geant4 Software license. *
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// ********************************************************************
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//
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//
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/// \file eventgenerator/pythia/pythia8decayer/include/Py8DecayerEngine.hh
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/// \file Py8DecayerEngine.hh
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/// \brief Definition of the Py8DecayerEngine class
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///
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/// \author J. Yarba; FNAL
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///
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#ifndef Py8DecayerEngine_H
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#define Py8DecayerEngine_H
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@@ -23,12 +23,10 @@
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// * acceptance of all terms of the Geant4 Software license. *
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// ********************************************************************
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//
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//
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/// \file eventgenerator/pythia/pythia8decayer/include/Py8DecayerPhysics
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/// \file Py8DecayerPhysics.hh
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/// \brief Definition of the Py8DecayerPhysics class
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///
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/// \author J. Yarba; FNAL
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///
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#ifndef Py8DecayerPhysics_H
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#define Py8DecayerPhysics_H
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@@ -23,12 +23,10 @@
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// * acceptance of all terms of the Geant4 Software license. *
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// ********************************************************************
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//
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//
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/// \file eventgenerator/pythia/pythia8decayer/include/SingleParticleGun.hh
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/// \file SingleParticleGun.hh
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/// \brief Definition of the SingleParticleGun class
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///
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/// \author J. Yarba; FNAL
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///
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#ifndef SingleParticleGun_H
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#define SingleParticleGun_H
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@@ -23,9 +23,8 @@
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// * acceptance of all terms of the Geant4 Software license. *
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// ********************************************************************
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//
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//
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/// \file eventgenerator/pythia/py8decayer/pythia8_decayer.cc
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/// \brief Main program of the pythia8_decayer example
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/// \file pythia8_decayer.cc
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/// \brief Main program of the pythia/py8decayer example
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#include "ActionInitialization.hh"
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#include "DetConstruction.hh"
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@@ -23,8 +23,7 @@
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// * acceptance of all terms of the Geant4 Software license. *
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// ********************************************************************
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//
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//
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/// \file eventgenerator/pythia/pythia8decayer/src/ActionInitialization.cc
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/// \file ActionInitialization.cc
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/// \brief Implementation of the ActionInitialization class
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#include "ActionInitialization.hh"
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@@ -23,8 +23,7 @@
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// * acceptance of all terms of the Geant4 Software license. *
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// ********************************************************************
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//
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//
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/// \file eventgenerator/pythia/pythia8decayer/src/DetConstruction.cc
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/// \file DetConstruction.cc
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/// \brief Implementation of the DetConstruction class
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///
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/// \author J. Yarba; FNAL
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@@ -23,9 +23,8 @@
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// * acceptance of all terms of the Geant4 Software license. *
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// ********************************************************************
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//
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//
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/// \file eventgenerator/pythia/pythia8decayer/src/Py8Decayer.cc
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/// \brief Implementation of the Py8Decayer class
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/// \file Py8Decayer.cc
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/// \brief Implementation of the Pythia8::Py8Decayer class
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///
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/// \author J. Yarba; FNAL
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@@ -23,8 +23,7 @@
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// * acceptance of all terms of the Geant4 Software license. *
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// ********************************************************************
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//
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//
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/// \file eventgenerator/pythia/pythia8decayer/src/Py8DecayerPhysics.cc
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/// \file Py8DecayerPhysics.cc
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/// \brief Implementation of the Py8DecayerPhysics class
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///
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/// \author J. Yarba; FNAL
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@@ -23,8 +23,7 @@
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// * acceptance of all terms of the Geant4 Software license. *
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// ********************************************************************
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//
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//
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/// \file eventgenerator/pythia/pythia8decayer/src/SingleParticleGun.cc
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/// \file SingleParticleGun.cc
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/// \brief Implementation of the SingleParticleGun class
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///
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/// \author J. Yarba; FNAL
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Reference in New Issue
Block a user