Example Keywords

Examles by Keyword

The Pythia examples directory contains about 100 examples, each showcasing one or several features of the framework. The examples are ordered by keyword below, and cross referenced, allowing for exploration of the various features. A new user may want to start with examples presenting the Basic Usage before going on to explore more advanced topics. Below, the search box can be used to search for keywords which will be displayed the box. This is followed by an expandable list of keywords with links. Finally, a full list of keywords and the relevant examples for each keyword is provided. The code for the example can be accessed by clicking on the name of the example.

● aMC@NLO ● Analysis ● Angantyr ● anti‑kT ● arXiv:2108.03481 [hep‑ph] ● Astroparticle ● B decays ● Basic usage ● Beam gas ● Beam momentum ● Biasing ● BSM ● Centrality ● Charged multiplicity ● Charm ● CKKW‑L ● Colour reconnection ● Command file ● Command line option ● Cosmic ray cascade ● Cross sections ● Cross sections. ● Dark matter ● Diffraction ● Dire ● DIS ● Displaced vertex ● DPS ● E+e‑ events ● Electron‑positron ● Event display ● Event filter ● Event record ● Event shapes ● EvtGen ● Exclusive ● External decays ● External derived class ● External resonance ● Extra dimensions ● Fastjet ● Fixed target ● Forward physics ● FxFx ● Gnuplot ● Hadron production ● Hadron widths ● Hadron‑ion collisions ● Hadronic rescattering ● Hadronization ● Hard diffraction ● HDF5 file ● Heavy ions ● Helaconia ● Hepmc ● Hidden Valley ● Higgs ● Histograms ● Jet finding ● Jets ● kT ● Leading order ● LHAPDF ● LHE file ● LHEF ● Lheh5 ● Low energy ● Madgraph ● MadGraph5_aMC@NLO ● Matching ● Matplotlib ● MC@NLO ● Merging ● MESS ● Minimum bias ● MLM ● MPI ● Multi‑instance ● Multiplicities ● NL3 ● NLO ● Onia ● OpenMP ● Optimization ● P pbar ● Parallelism ● Partial cross sections ● Particle data ● Parton distribution ● PDFs ● Performance ● Photon beam ● Photon‑photon ● Photoproduction ● Pileup ● Powheg ● Process cross sections ● Process selection ● Process veto ● Proton‑ion ● pT bias ● pT spectra ● Pythia 6 ● Python ● R‑hadron ● R‑hadrons ● Random number generator ● Rescattering ● Resonance decay ● Resonances ● reuse MPI initialization ● Reweighting ● Rivet ● Root ● Rope hadronization ● Second interaction ● Slowjet ● Space‑time picture ● String shoving ● Subruns ● Supersymmetry ● Switch beam ● Switch collision energy ● Tevatron ● Thermal model ● Top ● Top mass ● Total cross section ● Tuning ● Two‑body decay ● UMEPS ● Uncertainty bands ● UNLOPS ● UPC ● User hook ● Userhooks ● Utility ● Vertex spread ● Vincia ● Weak showers ● Z production

aMC@NLO

main151.cc: demonstrates MC@NLO matching with LHEF input from MadGraph5_aMC@NLO. Input is provided by the main151.cmnd file.
main153.cc: demonstrates how Madgraph5_aMC@NLO can be run "from within" Pythia, making use of the LHAupMadgraph wrapper/interface of Madgraph5_aMC@NLO and the Pythia jet matching facilities.
main164.cc: general main program to use Pythia's matching and merging schemes. Which method is used is specified by the .cmnd input file: main164mcatnlo.cmnd for MC@NLO matching with Madgraph5_aMC@NLO, main164powheg.cmnd for POWHEG matching with POWHEG-BOX, main164ckkwl.cmnd for CKKW-L merging, main164mess.cmnd for Vincia's CKKW-L sector merging (MESS), main164umeps.cmnd for UMEPS merging, main164unlops.cmnd for UNLOPS merging, main164mlm.cmnd for MLM jet matching, main164fxfx.cmnd for FxFx merging.
main295.py: a Python interface equivalent to main154.cc, with interface to Madgraph.

Analysis

main143.cc: shows how ROOT can be used for histogramming in a program that for the rest is structured like a normal PYTHIA run.
main144.cc: streamlined event generation with possibility to output ROOT files, output HepMC files and run RIVET analyses, all by specifying output modes in a cmnd file, where also the event generator settings are specified. The example is run with command line options, run ./main144 -h to see a full list. See ROOT Usage for information about ROOT output, RIVET Usage for information about RIVET and HepMC Interface for information about HepMC.
main231.cc: put all user analysis code into a class of its own, separate from the main program, and provide the "cards file" name as a command-line argument. Also exemplifies how Higgs mass, width and branching ratios can be set by hand.
main232.cc: shows how to write an event filter class, where you keep a vector of pointers to the subset of particles you want to study further. The event record itself remains unchanged.
main233.cc: example how to create a tailor-made copy of the ordinary event record, here with hard-process history tracing closer to the PYTHIA 6 conventions.
main262.cc: set up automatic uncertainty band variations to PDFs and factorization and renormalization scales.
main422.cc: p-Pb collisions at LHC energies, using the Angantyr model for Heavy Ion collisions, and analyzing events by centrality bins.

Angantyr

main421.cc: simple pp collisions as in main101.cc, but using the Angantyr model for Heavy Ion collisions. Also shows how Rivet analyses can be set up easily using a special interface.
main422.cc: p-Pb collisions at LHC energies, using the Angantyr model for Heavy Ion collisions, and analyzing events by centrality bins.
main423.cc: Pb-Pb collisions at LHC energies, using the Angantyr model for Heavy Ion collisions, and analyzing events by centrality bins.

anti‑kT

main242.cc: illustration how UserHooks can be used interact directly with the event-generation process.
main293.py: a Python interface equivalent to main242.cc. Demonstrates usage of a PYTHIA plugin within the Python interface.

arXiv:2108.03481 [hep‑ph]

main481.cc: plot PDFs for a large number of hadrons.
main482.cc: test switching between hadron beams on an event-by-event basis. Compare running times for different scenarios.

Astroparticle

main241.cc: set up a fictitious production process to a generic resonance, where you easily can compose your own list of (two-body) decay modes to a variety of final states. Also traces decay chains down to truly stable particles: gamma, e^+-, p/pbar and neutrinos. Suitable for astroparticle applications, like neutralino pair annihilation, where cross sections are calculated separately in another program. Also shows how to plot histograms using the Pyplot solution.

B decays

main361.cc: loop over several tries, either to redo B decays only or to redo the complete hadronization chain of an event. This is a way to increase efficiency, since much of the generation process is only made once.
main364.cc: demonstrates how to use the EvtGenDecays class provided by include/Pythia8Plugins/EvtGen.h to perform decays with the EvtGen package. The main364.dec header contains special instructions how to configure PYTHIA for use with EvtGen.

Basic usage

main101.cc: a simple study of the charged multiplicity for jet events at the LHC.
main102.cc: a simple study of the pT spectrum of Z bosons at the Tevatron.
main103.cc: basic generation of e^+e^- events at LEP 1.
main111.cc: basic generation of e^+e^- events at LEP 1, equivalent with main103.cmnd, but with settings delegated to the auxiliary main111.cmnd file.
main112.cc: a simple study of the pT spectrum of Z bosons at the Tevatron, with Pyplot option for displaying the result, but otherwise equivalent with main102.cc.
main113.cc: a simple study of several different kinds of events, with the choice to be made in the main113.cmnd "cards file". Also shows how to plot histograms using the Pyplot approach.
main121.cc: a study of top events, fed in from the Les Houches Event File ttbar.lhe, here generated by PYTHIA 6.4. This file currently only contains 100 events so as not to make the distributed PYTHIA package too big, and so serves mainly as a demonstration of the principles involved.
main122.cc: a more sophisticated variant of main121.cc, where two Les Houches Event Files (ttbar.lhe and ttbar2.lhe) successively are used as input. Also illustrating some other aspects, like the capability to mix in internally generated events.
main123.cc: a streamlined version of main122.cc, where two Les Houches Event Files (ttbar.lhe and ttbar2.lhe) successively are used as input in main123.cmnd file.
main124.cc: shows how PYTHIA 8 can write a Les Houches Event File, using facilities potentially useful also for other programs to write an LHEF. See also main125.cc.
main125.cc: exemplifies how LHEF version 3 events can be written on an external file.
main126.cc: shows how LHEF version 3.0 files can be read and used to fill several histograms of the same property, but with different event weights.
main127.cc: an extended version of main126.cc, where additionally it is shown how to extract many different kinds of LHEF version 3.0 information.
main131.cc: similar to main101, except that the event record is output in the HepMC event record format. Requires that HepMC3 is properly linked. Note that the main131.hepmc output file can become quite big; so no example is included in this distribution.
main132.cc: a streamlined version for the generation of events that are then stored in HepMC format, without any event analysis. That is, all physics studies will have to be done afterwards. The name of the input "cards file" (e.g. main132.cmnd) and output HepMC event file (e.g. main132.hepmc) are to be provided as command-line arguments. Requires that HepMC3 is properly linked. Note that the HepMC output file can become quite big; so no example is included in this distribution.
main135.cc: illustrates how the event record can be compressed to include e.g. only the final-state particles, in order to reduce the HepMC file size, but obviously at the expense of losing some history information.
main211.cc: generation of QCD jet events at the LHC, with jet analysis using the SlowJet inclusive anti-kT sequential-recombination finder.
main213.cc: a comparison of SlowJet and FastJet jet finding, showing that they find the same jets if run under identical conditions, in this case for QCD jets.
main214.cc: a comparison of jet properties on the parton and the hadron level, illustrating possibilities for larger control of which particles are used in the jet analyses.
main216.cc: reconstruction of a hypothetical 1 TeV Z' mass by forming the invariant mass of the two jets with highest transverse momentum. Convenient starting point for student exercises.
main231.cc: put all user analysis code into a class of its own, separate from the main program, and provide the "cards file" name as a command-line argument. Also exemplifies how Higgs mass, width and branching ratios can be set by hand.
main291.py: a Python interface equivalent to main101.cc, i.e. a minimal example.
main301.cc: generation of LEP1 hadronic events, i.e. e^+e^- → gamma*/Z^0 → q qbar, with charged multiplicity, sphericity, thrust and jet analysis.
main321.cc: tests of cross sections, multiplicities and average transverse momenta for elastic, diffractive and nondiffractive topologies, using main321.cmnd to pick processes. For photoproduction one can use the alternative main321photons.cmnd input.
main322.cc: generation of the QCD jet cross section biased towards higher pT values, by two different techniques. Firstly, by splitting the run into subruns, each in its own pT bin, and adding the results properly reweighted. Two suboptions, with limits set either in the main program or by subrun specification in the main322.cmnd file. Secondly, by a continuous reweighting with a pT^4 bias in the selection, compensated by a 1/pT^4 event weight. Also inclusion of soft processes is illustrated, with subruns and weighted events.
main341.cc: demonstrates how to generate Deeply Inelastic Scattering events, e.g. in a HERA configuration.
main501.cc: tests of internally implemented cross sections for Supersymmetric particle production, with SUSY spectrum defined in slha2-example.spc and settings in main501.cmnd. For illustration, an alternative example spectrum is also available, sps1aWithDecays.spc, which contains a decay table in SLHA format.
main502.cc: input RPV-SUSY events from an LHEF file that contains an SLHA spectrum inside its header. The event file, main502.lhe, contains a sample events that illustrate how to arrange color tags in the presence of the color-space epsilon tensors that accompany baryon number violating event topologies.
main508.cc: simple setup for Dark Matter production in several different scenarios, as specified in main508.cmnd, notably with long-lived particle signatures.

Beam gas

main324.cc: use several instances of Pythia, one for signal events and others for a variable number of pileup and "beam-gas" events, combined into one common event record. Illustrates how new Pythia instances can copy existing settings and particle data.

Beam momentum

main245.cc: shows how to write external classes, derived from PYTHIA base classes, that can be handed to PYTHIA for internal generation. The MIXMAX random number generator is this way compared with the default PYTHIA one. Explicit implementations are included for the generation of external beam momentum spread and vertex location, and for a simple scaling external parton distribution set.

Biasing

main261.cc: exemplifies how rare emissions can be enhanced in the shower.
main322.cc: generation of the QCD jet cross section biased towards higher pT values, by two different techniques. Firstly, by splitting the run into subruns, each in its own pT bin, and adding the results properly reweighted. Two suboptions, with limits set either in the main program or by subrun specification in the main322.cmnd file. Secondly, by a continuous reweighting with a pT^4 bias in the selection, compensated by a 1/pT^4 event weight. Also inclusion of soft processes is illustrated, with subruns and weighted events.
main323.cc: generation of two predetermined hard interactions in each event.

BSM

main501.cc: tests of internally implemented cross sections for Supersymmetric particle production, with SUSY spectrum defined in slha2-example.spc and settings in main501.cmnd. For illustration, an alternative example spectrum is also available, sps1aWithDecays.spc, which contains a decay table in SLHA format.
main503.cc: test program for processes in scenarios with large extra dimensions or unparticles.
main504.cc: production of Kaluza-Klein gamma/Z states in TeV-sized extra dimensions.
main505.cc: production of long-lived R-hadrons, that are forced to decay at separate vertices and possibly with changed momenta.
main507.cc: setup (in main507.cmnd) for Dark Matter production via an s-channel mediator, where a mono-jet pT spectrum is found with the FastJet package.
main508.cc: simple setup for Dark Matter production in several different scenarios, as specified in main508.cmnd, notably with long-lived particle signatures.

Centrality

main422.cc: p-Pb collisions at LHC energies, using the Angantyr model for Heavy Ion collisions, and analyzing events by centrality bins.
main423.cc: Pb-Pb collisions at LHC energies, using the Angantyr model for Heavy Ion collisions, and analyzing events by centrality bins.

Charged multiplicity

main101.cc: a simple study of the charged multiplicity for jet events at the LHC.
main103.cc: basic generation of e^+e^- events at LEP 1.
main222.cc: equivalent to main221.cc, but is much more heavily commented to give more in-depth explanations of how the code works.
main291.py: a Python interface equivalent to main101.cc, i.e. a minimal example.
main292.py: a Python interface equivalent to main222.cc. Provides an example of how to derive PYTHIA classes in Python.
main422.cc: p-Pb collisions at LHC energies, using the Angantyr model for Heavy Ion collisions, and analyzing events by centrality bins.
main423.cc: Pb-Pb collisions at LHC energies, using the Angantyr model for Heavy Ion collisions, and analyzing events by centrality bins.

Charm

main366.cc: calculates charm hadron asymmetries in fixed-target pi^- p collisions, and compares results with data at three reasonably nearby energies.A few options are available, e.g. the QCDCR model.

CKKW‑L

main162.cc:
main162.cc exemplifies various multi-jet merging schemes in Pythia, depending on the .cmnd input file: main162ckkwl.cmnd for CKKW-L, main162umeps.cmnd for UMEPS, main162nl3.cmnd for NL3, main162unlops.cmnd for UNLOPS, main162mess.cmnd for Vincia's CKKW-L sector merging (MESS).
main164.cc: general main program to use Pythia's matching and merging schemes. Which method is used is specified by the .cmnd input file: main164mcatnlo.cmnd for MC@NLO matching with Madgraph5_aMC@NLO, main164powheg.cmnd for POWHEG matching with POWHEG-BOX, main164ckkwl.cmnd for CKKW-L merging, main164mess.cmnd for Vincia's CKKW-L sector merging (MESS), main164umeps.cmnd for UMEPS merging, main164unlops.cmnd for UNLOPS merging, main164mlm.cmnd for MLM jet matching, main164fxfx.cmnd for FxFx merging.

Colour reconnection

main302.cc: colour reconnection rate in e^+e^- → W^+W^- → q_1 qbar_2 q_3 qbar_4 as a function of the collision energy.
main362.cc: colour reconnection models studied for top production. Illustrates how to set up the user hooks in include/Pythia8Plugins/ColourReconnectionHooks.h, with several models not found in the standard PYTHIA library.
main441.cc: shows how the string shoving mechanism, part of the rope hadronization framework, can be set up and used to generate ridge effects.
main442.cc: shows how flavour production is changed in the rope hadronization framework.

Command file

main111.cc: basic generation of e^+e^- events at LEP 1, equivalent with main103.cmnd, but with settings delegated to the auxiliary main111.cmnd file.
main113.cc: a simple study of several different kinds of events, with the choice to be made in the main113.cmnd "cards file". Also shows how to plot histograms using the Pyplot approach.
main123.cc: a streamlined version of main122.cc, where two Les Houches Event Files (ttbar.lhe and ttbar2.lhe) successively are used as input in main123.cmnd file.
main132.cc: a streamlined version for the generation of events that are then stored in HepMC format, without any event analysis. That is, all physics studies will have to be done afterwards. The name of the input "cards file" (e.g. main132.cmnd) and output HepMC event file (e.g. main132.hepmc) are to be provided as command-line arguments. Requires that HepMC3 is properly linked. Note that the HepMC output file can become quite big; so no example is included in this distribution.
main133.cc: a further extension of main132.cc, where subruns are used to process several consecutive LHEF, as in main123.cc, with information stored e.g in main133.cmnd. Other comments as for main132.cc.
main144.cc: streamlined event generation with possibility to output ROOT files, output HepMC files and run RIVET analyses, all by specifying output modes in a cmnd file, where also the event generator settings are specified. The example is run with command line options, run ./main144 -h to see a full list. See ROOT Usage for information about ROOT output, RIVET Usage for information about RIVET and HepMC Interface for information about HepMC.
main224.cc: allows to steer Pythia from the command line, can produce HepMC files, and allows for OpenMP parallelization. More documentation can be obtained by executing ./main224 --help. The input file main224.cmnd further illustrates the use of DIRE.
main231.cc: put all user analysis code into a class of its own, separate from the main program, and provide the "cards file" name as a command-line argument. Also exemplifies how Higgs mass, width and branching ratios can be set by hand.
main248.cc: shows how to use a filter to select a specific final state from resonance decays.
main321.cc: tests of cross sections, multiplicities and average transverse momenta for elastic, diffractive and nondiffractive topologies, using main321.cmnd to pick processes. For photoproduction one can use the alternative main321photons.cmnd input.
main501.cc: tests of internally implemented cross sections for Supersymmetric particle production, with SUSY spectrum defined in slha2-example.spc and settings in main501.cmnd. For illustration, an alternative example spectrum is also available, sps1aWithDecays.spc, which contains a decay table in SLHA format.

Command line option

main132.cc: a streamlined version for the generation of events that are then stored in HepMC format, without any event analysis. That is, all physics studies will have to be done afterwards. The name of the input "cards file" (e.g. main132.cmnd) and output HepMC event file (e.g. main132.hepmc) are to be provided as command-line arguments. Requires that HepMC3 is properly linked. Note that the HepMC output file can become quite big; so no example is included in this distribution.
main144.cc: streamlined event generation with possibility to output ROOT files, output HepMC files and run RIVET analyses, all by specifying output modes in a cmnd file, where also the event generator settings are specified. The example is run with command line options, run ./main144 -h to see a full list. See ROOT Usage for information about ROOT output, RIVET Usage for information about RIVET and HepMC Interface for information about HepMC.
main224.cc: allows to steer Pythia from the command line, can produce HepMC files, and allows for OpenMP parallelization. More documentation can be obtained by executing ./main224 --help. The input file main224.cmnd further illustrates the use of DIRE.
main231.cc: put all user analysis code into a class of its own, separate from the main program, and provide the "cards file" name as a command-line argument. Also exemplifies how Higgs mass, width and branching ratios can be set by hand.

Cosmic ray cascade

main483.cc: simple example of how Pythia can be used to simulate a basic hadronic cascade in the atmosphere.
main484.cc: as main483.cc, but using the PythiaCascade class to perform the separate collisions or decays, while the bookkeeping of the cascade evolution remains in the main program.
main485.cc: an even simpler example of one collision or decay at a time, as performed in PythiaCascade.

Cross sections

main321.cc: tests of cross sections, multiplicities and average transverse momenta for elastic, diffractive and nondiffractive topologies, using main321.cmnd to pick processes. For photoproduction one can use the alternative main321photons.cmnd input.
main464.cc: plot the energy dependence of the low-energy cross sections used in the hadronic rescattering framework.
main465.cc: plot the energy dependence of the low-energy cross sections, specifically the contribution from resonances.

Cross sections.

main425.cc: calculates the proton-oxygen cross section at varying energies.

Dark matter

main407.cc: VINCIA electroweak showers off an LHEF file for dark-matter annihilation. The VINCIA EW shower requires hard-process partons with assigned helicities. In this example, these are read in from the LHEF file.
main507.cc: setup (in main507.cmnd) for Dark Matter production via an s-channel mediator, where a mono-jet pT spectrum is found with the FastJet package.

Diffraction

main321.cc: tests of cross sections, multiplicities and average transverse momenta for elastic, diffractive and nondiffractive topologies, using main321.cmnd to pick processes. For photoproduction one can use the alternative main321photons.cmnd input.
main325.cc: exemplifies the generation of hard diffractive processes.
main342.cc: exemplifies hard diffraction in the context of a photon-inside-lepton beam, like at HERA.

Dire

main224.cc: allows to steer Pythia from the command line, can produce HepMC files, and allows for OpenMP parallelization. More documentation can be obtained by executing ./main224 --help. The input file main224.cmnd further illustrates the use of DIRE.
main401.cc: simple example of the VINCIA (or DIRE) shower model(s), on Z decays at LEP I, with some basic event shapes, spectra, and multiplicity counts.
main402.cc: comparison of VINCIA and Pythia on inclusive jets at LHC, with option to run the two generators in parallel using OpenMP. See main204.cc for how to do this with the Parallelism framework.
main403.cc: VINCIA setup for ttbar production at LHC, with measurement of run time and options to switch various shower and MPI/hadronization components on/off via command file.
main404.cc: demonstrates the example of main201 using the Parallelism framework.

DIS

main341.cc: demonstrates how to generate Deeply Inelastic Scattering events, e.g. in a HERA configuration.
main342.cc: exemplifies hard diffraction in the context of a photon-inside-lepton beam, like at HERA.
main344.cc: exemplifies how to provide an external photon flux for photo-production processes.

Displaced vertex

main505.cc: production of long-lived R-hadrons, that are forced to decay at separate vertices and possibly with changed momenta.

DPS

main326.cc: example on how double parton scattering events can be reweighted according to a different model than default in Pythia. Contributed by Boris Blok and Paolo Gunnellini.

E+e‑ events

main302.cc: colour reconnection rate in e^+e^- → W^+W^- → q_1 qbar_2 q_3 qbar_4 as a function of the collision energy.

Electron‑positron

main103.cc: basic generation of e^+e^- events at LEP 1.
main111.cc: basic generation of e^+e^- events at LEP 1, equivalent with main103.cmnd, but with settings delegated to the auxiliary main111.cmnd file.
main301.cc: generation of LEP1 hadronic events, i.e. e^+e^- → gamma*/Z^0 → q qbar, with charged multiplicity, sphericity, thrust and jet analysis.
main381.cc: Higgs production in an 500 GeV e^+e^- coillider, illustrating the composition of production channels and the charged multiplicity arising in each of them.
main401.cc: simple example of the VINCIA (or DIRE) shower model(s), on Z decays at LEP I, with some basic event shapes, spectra, and multiplicity counts.

Event display

main141.cc: use ROOT to visualize the particles produced by Pythia in (y,phi) space.
main142.cc: use ROOT to visualize different jet algoritms in (y,phi) space. The jet clustering is done with FastJet. The produced figure was used in the article "50 years of Quantum Chromodynamics" in celebration of the 50th anniversary of QCD (EPJC).

Event filter

main232.cc: shows how to write an event filter class, where you keep a vector of pointers to the subset of particles you want to study further. The event record itself remains unchanged.

Event record

main233.cc: example how to create a tailor-made copy of the ordinary event record, here with hard-process history tracing closer to the PYTHIA 6 conventions.

Event shapes

main301.cc: generation of LEP1 hadronic events, i.e. e^+e^- → gamma*/Z^0 → q qbar, with charged multiplicity, sphericity, thrust and jet analysis.

EvtGen

main364.cc: demonstrates how to use the EvtGenDecays class provided by include/Pythia8Plugins/EvtGen.h to perform decays with the EvtGen package. The main364.dec header contains special instructions how to configure PYTHIA for use with EvtGen.

Exclusive

main345.cc: demonstrates how to generate different types of photon-initiated dilepton events in proton-proton collisions.

External decays

main243.cc: shows (a) how to use UserHooks to regularize onium cross section for pT → 0, and (b) how decays could be handled externally.
main364.cc: demonstrates how to use the EvtGenDecays class provided by include/Pythia8Plugins/EvtGen.h to perform decays with the EvtGen package. The main364.dec header contains special instructions how to configure PYTHIA for use with EvtGen.

External derived class

main245.cc: shows how to write external classes, derived from PYTHIA base classes, that can be handed to PYTHIA for internal generation. The MIXMAX random number generator is this way compared with the default PYTHIA one. Explicit implementations are included for the generation of external beam momentum spread and vertex location, and for a simple scaling external parton distribution set.

External resonance

main244.cc: shows how an external resonance can be implemented as a new class derived from a PYTHIA base class, and be used in an external process, both of them handed in for generation as with normal internal classes.
main246.cc: illustrates how a user hook can be made to steer the angular distribution selection in resonance decays. The prime example would be if LHEF input, e.g. from Madgraph, contains undecayed resonances with helicity information. These would then be decayed isotropically by PYTHIA, but this example shows how one could do better. Some input in main246.cmnd.

Extra dimensions

main503.cc: test program for processes in scenarios with large extra dimensions or unparticles.
main504.cc: production of Kaluza-Klein gamma/Z states in TeV-sized extra dimensions.

Fastjet

main161.cc: exemplifies CKKW-L merging with a user-defined merging scale. Input is provided by the main161.cmnd file.
main212.cc: an example how the FastJet jet finding package can be linked to allow an analysis of the final state, in this case for a study of W + jet production.
main213.cc: a comparison of SlowJet and FastJet jet finding, showing that they find the same jets if run under identical conditions, in this case for QCD jets.
main215.cc: exemplifies how to use one of the contributed add-ons to the FastJet package. In this case the modified Mass Drop Tagger is used to improve the mass reconstruction of a boosted hadronically decaying Z^0.
main507.cc: setup (in main507.cmnd) for Dark Matter production via an s-channel mediator, where a mono-jet pT spectrum is found with the FastJet package.

Fixed target

main324.cc: use several instances of Pythia, one for signal events and others for a variable number of pileup and "beam-gas" events, combined into one common event record. Illustrates how new Pythia instances can copy existing settings and particle data.
main366.cc: calculates charm hadron asymmetries in fixed-target pi^- p collisions, and compares results with data at three reasonably nearby energies.A few options are available, e.g. the QCDCR model.

Forward physics

main327.cc: study forward proton production in a 7 TeV sample of inelastic events, both diffractive and nondiffractive. Compare default, ditto without popcorn for remnant diquark, and the QCDCR model.

FxFx

main164.cc: general main program to use Pythia's matching and merging schemes. Which method is used is specified by the .cmnd input file: main164mcatnlo.cmnd for MC@NLO matching with Madgraph5_aMC@NLO, main164powheg.cmnd for POWHEG matching with POWHEG-BOX, main164ckkwl.cmnd for CKKW-L merging, main164mess.cmnd for Vincia's CKKW-L sector merging (MESS), main164umeps.cmnd for UMEPS merging, main164unlops.cmnd for UNLOPS merging, main164mlm.cmnd for MLM jet matching, main164fxfx.cmnd for FxFx merging.

Gnuplot

main262.cc: set up automatic uncertainty band variations to PDFs and factorization and renormalization scales.

Hadron production

main327.cc: study forward proton production in a 7 TeV sample of inelastic events, both diffractive and nondiffractive. Compare default, ditto without popcorn for remnant diquark, and the QCDCR model.

Hadron widths

main466.cc: perform parameterization of hadron widths and output the resulting tables.

Hadron‑ion collisions

main424.cc: variable beam energy and types for hadron-ion collisions, where the initialization can be cached for later use.

Hadronic rescattering

main247.cc: illustrates the use of UserHooks to veto events after hadronization, but before any subsequent processes such as rescattering or Bose-Einstein.
main469.cc: show as a function of time and distance, from 1 fm to 1 m, how particles are produced, decay and rescatter.

Hadronization

main214.cc: a comparison of jet properties on the parton and the hadron level, illustrating possibilities for larger control of which particles are used in the jet analyses.
main234.cc: an example how a single particle or various parton-level configurations can be input directly for hadronization, without being tied to the full process-generation machinery, e.g. to study the hadronization of junction topologies. Can also be used for single-resonance decays, with showers.
main263.cc: demonstrates the use of in-situ hadronization reweighting for variations of both kinematic and flavor hadronization parameters. The output compares multiplicity distributions from the default parameters to the reweighted output with the varied parameters and the output using the varied parameters without reweighting.
main329.cc: comparison of charged multiplicity distributions with data at 200 (UA5), 900 (UA5) and 1800 (E735) GeV.
main361.cc: loop over several tries, either to redo B decays only or to redo the complete hadronization chain of an event. This is a way to increase efficiency, since much of the generation process is only made once.
main362.cc: colour reconnection models studied for top production. Illustrates how to set up the user hooks in include/Pythia8Plugins/ColourReconnectionHooks.h, with several models not found in the standard PYTHIA library.
main441.cc: shows how the string shoving mechanism, part of the rope hadronization framework, can be set up and used to generate ridge effects.
main442.cc: shows how flavour production is changed in the rope hadronization framework.
main502.cc: input RPV-SUSY events from an LHEF file that contains an SLHA spectrum inside its header. The event file, main502.lhe, contains a sample events that illustrate how to arrange color tags in the presence of the color-space epsilon tensors that accompany baryon number violating event topologies.

Hard diffraction

main342.cc: exemplifies hard diffraction in the context of a photon-inside-lepton beam, like at HERA.

HDF5 file

main136.cc: an example illustrating the generation of HepMC events using the HDF5 LHA format (LHAHDF5).

Heavy ions

main344.cc: exemplifies how to provide an external photon flux for photo-production processes.
main421.cc: simple pp collisions as in main101.cc, but using the Angantyr model for Heavy Ion collisions. Also shows how Rivet analyses can be set up easily using a special interface.
main422.cc: p-Pb collisions at LHC energies, using the Angantyr model for Heavy Ion collisions, and analyzing events by centrality bins.
main423.cc: Pb-Pb collisions at LHC energies, using the Angantyr model for Heavy Ion collisions, and analyzing events by centrality bins.
main425.cc: calculates the proton-oxygen cross section at varying energies.

Helaconia

main363.cc: demonstrates how to generate quarkonia events with the external HelacOnia package interfaced to Pythia, and compare results with the internal implementation.

Hepmc

main131.cc: similar to main101, except that the event record is output in the HepMC event record format. Requires that HepMC3 is properly linked. Note that the main131.hepmc output file can become quite big; so no example is included in this distribution.
main132.cc: a streamlined version for the generation of events that are then stored in HepMC format, without any event analysis. That is, all physics studies will have to be done afterwards. The name of the input "cards file" (e.g. main132.cmnd) and output HepMC event file (e.g. main132.hepmc) are to be provided as command-line arguments. Requires that HepMC3 is properly linked. Note that the HepMC output file can become quite big; so no example is included in this distribution.
main133.cc: a further extension of main132.cc, where subruns are used to process several consecutive LHEF, as in main123.cc, with information stored e.g in main133.cmnd. Other comments as for main132.cc.
main134.cc:
main134.cc (was main44.cc and a legacy HepMC2 example, alternatively HepMC3, where subruns are used to process several consecutive LHEF, with information stored e.g in main134.cmnd.
main135.cc: illustrates how the event record can be compressed to include e.g. only the final-state particles, in order to reduce the HepMC file size, but obviously at the expense of losing some history information.
main136.cc: an example illustrating the generation of HepMC events using the HDF5 LHA format (LHAHDF5).
main144.cc: streamlined event generation with possibility to output ROOT files, output HepMC files and run RIVET analyses, all by specifying output modes in a cmnd file, where also the event generator settings are specified. The example is run with command line options, run ./main144 -h to see a full list. See ROOT Usage for information about ROOT output, RIVET Usage for information about RIVET and HepMC Interface for information about HepMC.
main164.cc: general main program to use Pythia's matching and merging schemes. Which method is used is specified by the .cmnd input file: main164mcatnlo.cmnd for MC@NLO matching with Madgraph5_aMC@NLO, main164powheg.cmnd for POWHEG matching with POWHEG-BOX, main164ckkwl.cmnd for CKKW-L merging, main164mess.cmnd for Vincia's CKKW-L sector merging (MESS), main164umeps.cmnd for UMEPS merging, main164unlops.cmnd for UNLOPS merging, main164mlm.cmnd for MLM jet matching, main164fxfx.cmnd for FxFx merging.
main224.cc: allows to steer Pythia from the command line, can produce HepMC files, and allows for OpenMP parallelization. More documentation can be obtained by executing ./main224 --help. The input file main224.cmnd further illustrates the use of DIRE.

Hidden Valley

main509.cc: three scenarios for Hidden Valley particle production at 13 TeV, with a selection of further possible variations.
main510.cc: a related setup of a few different scenarios for Hidden Valley particle production at a 1 TeV e^+e^- collider.

Higgs

main381.cc: Higgs production in an 500 GeV e^+e^- coillider, illustrating the composition of production channels and the charged multiplicity arising in each of them.

Histograms

main401.cc: simple example of the VINCIA (or DIRE) shower model(s), on Z decays at LEP I, with some basic event shapes, spectra, and multiplicity counts.

Jet finding

main161.cc: exemplifies CKKW-L merging with a user-defined merging scale. Input is provided by the main161.cmnd file.
main211.cc: generation of QCD jet events at the LHC, with jet analysis using the SlowJet inclusive anti-kT sequential-recombination finder.
main212.cc: an example how the FastJet jet finding package can be linked to allow an analysis of the final state, in this case for a study of W + jet production.
main213.cc: a comparison of SlowJet and FastJet jet finding, showing that they find the same jets if run under identical conditions, in this case for QCD jets.
main214.cc: a comparison of jet properties on the parton and the hadron level, illustrating possibilities for larger control of which particles are used in the jet analyses.
main215.cc: exemplifies how to use one of the contributed add-ons to the FastJet package. In this case the modified Mass Drop Tagger is used to improve the mass reconstruction of a boosted hadronically decaying Z^0.
main216.cc: reconstruction of a hypothetical 1 TeV Z' mass by forming the invariant mass of the two jets with highest transverse momentum. Convenient starting point for student exercises.
main242.cc: illustration how UserHooks can be used interact directly with the event-generation process.
main293.py: a Python interface equivalent to main242.cc. Demonstrates usage of a PYTHIA plugin within the Python interface.
main301.cc: generation of LEP1 hadronic events, i.e. e^+e^- → gamma*/Z^0 → q qbar, with charged multiplicity, sphericity, thrust and jet analysis.
main507.cc: setup (in main507.cmnd) for Dark Matter production via an s-channel mediator, where a mono-jet pT spectrum is found with the FastJet package.

Jets

main142.cc: use ROOT to visualize different jet algoritms in (y,phi) space. The jet clustering is done with FastJet. The produced figure was used in the article "50 years of Quantum Chromodynamics" in celebration of the 50th anniversary of QCD (EPJC).
main247.cc: illustrates the use of UserHooks to veto events after hadronization, but before any subsequent processes such as rescattering or Bose-Einstein.
main342.cc: exemplifies hard diffraction in the context of a photon-inside-lepton beam, like at HERA.

kT

main161.cc: exemplifies CKKW-L merging with a user-defined merging scale. Input is provided by the main161.cmnd file.

Leading order

main161.cc: exemplifies CKKW-L merging with a user-defined merging scale. Input is provided by the main161.cmnd file.
main164.cc: general main program to use Pythia's matching and merging schemes. Which method is used is specified by the .cmnd input file: main164mcatnlo.cmnd for MC@NLO matching with Madgraph5_aMC@NLO, main164powheg.cmnd for POWHEG matching with POWHEG-BOX, main164ckkwl.cmnd for CKKW-L merging, main164mess.cmnd for Vincia's CKKW-L sector merging (MESS), main164umeps.cmnd for UMEPS merging, main164unlops.cmnd for UNLOPS merging, main164mlm.cmnd for MLM jet matching, main164fxfx.cmnd for FxFx merging.

LHAPDF

main201.cc: a test of the shape of parton densities, as a check prior to using a given PDF set in a generator. Requires that LHAPDF is properly linked. Also shows how to plot histograms (with logarithmic x scale) using the Pyplot solution.
main202.cc: compares the charged multiplicity distribution, and a few other minimum-bias physics aspects, between default PYTHIA PDF and another one. Requires that LHAPDF is properly linked.
main203.cc: compares the internal and LHAPDF implementations of the NNPDF 2.3 QCD+QED sets, for results and for timing. Requires that LHAPDF is properly linked.
main204.cc: tests the possibility to do backwards evolution from an incoming photon at the hard interaction. Input in main204.cmnd and photoninproton.lhe. Requires that you link to a LHAPDF set that includes the photon PDF.

LHE file

main121.cc: a study of top events, fed in from the Les Houches Event File ttbar.lhe, here generated by PYTHIA 6.4. This file currently only contains 100 events so as not to make the distributed PYTHIA package too big, and so serves mainly as a demonstration of the principles involved.
main122.cc: a more sophisticated variant of main121.cc, where two Les Houches Event Files (ttbar.lhe and ttbar2.lhe) successively are used as input. Also illustrating some other aspects, like the capability to mix in internally generated events.
main123.cc: a streamlined version of main122.cc, where two Les Houches Event Files (ttbar.lhe and ttbar2.lhe) successively are used as input in main123.cmnd file.
main124.cc: shows how PYTHIA 8 can write a Les Houches Event File, using facilities potentially useful also for other programs to write an LHEF. See also main125.cc.
main125.cc: exemplifies how LHEF version 3 events can be written on an external file.
main126.cc: shows how LHEF version 3.0 files can be read and used to fill several histograms of the same property, but with different event weights.
main127.cc: an extended version of main126.cc, where additionally it is shown how to extract many different kinds of LHEF version 3.0 information.
main132.cc: a streamlined version for the generation of events that are then stored in HepMC format, without any event analysis. That is, all physics studies will have to be done afterwards. The name of the input "cards file" (e.g. main132.cmnd) and output HepMC event file (e.g. main132.hepmc) are to be provided as command-line arguments. Requires that HepMC3 is properly linked. Note that the HepMC output file can become quite big; so no example is included in this distribution.
main133.cc: a further extension of main132.cc, where subruns are used to process several consecutive LHEF, as in main123.cc, with information stored e.g in main133.cmnd. Other comments as for main132.cc.
main134.cc:
main134.cc (was main44.cc and a legacy HepMC2 example, alternatively HepMC3, where subruns are used to process several consecutive LHEF, with information stored e.g in main134.cmnd.
main164.cc: general main program to use Pythia's matching and merging schemes. Which method is used is specified by the .cmnd input file: main164mcatnlo.cmnd for MC@NLO matching with Madgraph5_aMC@NLO, main164powheg.cmnd for POWHEG matching with POWHEG-BOX, main164ckkwl.cmnd for CKKW-L merging, main164mess.cmnd for Vincia's CKKW-L sector merging (MESS), main164umeps.cmnd for UMEPS merging, main164unlops.cmnd for UNLOPS merging, main164mlm.cmnd for MLM jet matching, main164fxfx.cmnd for FxFx merging.
main246.cc: illustrates how a user hook can be made to steer the angular distribution selection in resonance decays. The prime example would be if LHEF input, e.g. from Madgraph, contains undecayed resonances with helicity information. These would then be decayed isotropically by PYTHIA, but this example shows how one could do better. Some input in main246.cmnd.
main502.cc: input RPV-SUSY events from an LHEF file that contains an SLHA spectrum inside its header. The event file, main502.lhe, contains a sample events that illustrate how to arrange color tags in the presence of the color-space epsilon tensors that accompany baryon number violating event topologies.

LHEF

main407.cc: VINCIA electroweak showers off an LHEF file for dark-matter annihilation. The VINCIA EW shower requires hard-process partons with assigned helicities. In this example, these are read in from the LHEF file.

Lheh5

main136.cc: an example illustrating the generation of HepMC events using the HDF5 LHA format (LHAHDF5).

Low energy

main461.cc: compare the energy dependence of the average charged multiplicity between the simple treatment in rescattering and the full framework.
main462.cc: compare multiplicities and pT spectra with or without rescattering, the former with or without rescattering between nearest neighbours along the string.
main463.cc: simple generation of low-energy events.
main464.cc: plot the energy dependence of the low-energy cross sections used in the hadronic rescattering framework.
main465.cc: plot the energy dependence of the low-energy cross sections, specifically the contribution from resonances.
main467.cc: generate tetraquarks from the rescattering of a D0 and Dbar*0 beam.
main468.cc: generate tetraquarks from the rescattering of D0 and Dbar*0 mesons produced in LHC events.

Madgraph

main153.cc: demonstrates how Madgraph5_aMC@NLO can be run "from within" Pythia, making use of the LHAupMadgraph wrapper/interface of Madgraph5_aMC@NLO and the Pythia jet matching facilities.
main164.cc: general main program to use Pythia's matching and merging schemes. Which method is used is specified by the .cmnd input file: main164mcatnlo.cmnd for MC@NLO matching with Madgraph5_aMC@NLO, main164powheg.cmnd for POWHEG matching with POWHEG-BOX, main164ckkwl.cmnd for CKKW-L merging, main164mess.cmnd for Vincia's CKKW-L sector merging (MESS), main164umeps.cmnd for UMEPS merging, main164unlops.cmnd for UNLOPS merging, main164mlm.cmnd for MLM jet matching, main164fxfx.cmnd for FxFx merging.
main295.py: a Python interface equivalent to main154.cc, with interface to Madgraph.
main405.cc: VINCIA setup for electroweak shower off a fictitious process for Z decay to neutrinos at high mass. (In the absence of a weak shower, these would not shower at all.) The VINCIA EW shower requires hard-process partons with assigned helicities. This is done via Pythia's MG5 matrix-element interface, which must be compiled and linked (using configure --with-mg5mes).
main406.cc: previously main203.cc VINCIA setup for electroweak shower off high-pT dijets at the LHC. The VINCIA EW shower requires hard-process partons with assigned helicities. This is done via Pythia's MG5 matrix-element interface, which must be compiled and linked (using configure --with-mg5mes).

MadGraph5_aMC@NLO

main151.cc: demonstrates MC@NLO matching with LHEF input from MadGraph5_aMC@NLO. Input is provided by the main151.cmnd file.

Matching

main152.cc: exemplifies an improved matching of parton showers to LHEF-style input based on the POWHEG approach. The main152.cmnd allows to switch between several different matching options. It also allows to select input process, in this case either for the POWHEG-hvq program applied to top pair production Cor10 or for QCD 2+3-jet events. The small samples of input events are stored in the powheg-hvq.lhe and powheg-dijets.lhe files, respectively.
main153.cc: demonstrates how Madgraph5_aMC@NLO can be run "from within" Pythia, making use of the LHAupMadgraph wrapper/interface of Madgraph5_aMC@NLO and the Pythia jet matching facilities.
main154.cc: demonstrates how to link the POWHEGBOX matrix element programs dynamically, bypassing the need for intermediate LHE files. Two special files are used in this option: include/Pythia8Plugins/LHAPowheg.h contains the LHAup class wrapper used to build the POWHEG plugin libraries, and include/Pythia8Plugins/PowhegProcs.h the simple class that facilitates loading the POWHEG plugins. In addition main154.cmnd contains the commands needed for POWHEGBOX to run the example.
main163.cc: exemplifies MLM merging, either in the ALPGEN variant or in the Madgraph one, and with input events either from ALPGEN or from Madgraph, with relevant control cards stored in main163.cmnd. See Jet Matching for further details. Traditionally the ALPGEN output is split into one file with events and another with parameters and cross sections (unlike in LHEF). Here a sample of W + 3 jets events is stored in main163.unw and the parameters to go with it in main163_unw.par. Madgraph events are taken from the w+_production_lhc_2.lhe file in this case.
main164.cc: general main program to use Pythia's matching and merging schemes. Which method is used is specified by the .cmnd input file: main164mcatnlo.cmnd for MC@NLO matching with Madgraph5_aMC@NLO, main164powheg.cmnd for POWHEG matching with POWHEG-BOX, main164ckkwl.cmnd for CKKW-L merging, main164mess.cmnd for Vincia's CKKW-L sector merging (MESS), main164umeps.cmnd for UMEPS merging, main164unlops.cmnd for UNLOPS merging, main164mlm.cmnd for MLM jet matching, main164fxfx.cmnd for FxFx merging.
main295.py: a Python interface equivalent to main154.cc, with interface to Madgraph.

Matplotlib

main112.cc: a simple study of the pT spectrum of Z bosons at the Tevatron, with Pyplot option for displaying the result, but otherwise equivalent with main102.cc.
main113.cc: a simple study of several different kinds of events, with the choice to be made in the main113.cmnd "cards file". Also shows how to plot histograms using the Pyplot approach.
main122.cc: a more sophisticated variant of main121.cc, where two Les Houches Event Files (ttbar.lhe and ttbar2.lhe) successively are used as input. Also illustrating some other aspects, like the capability to mix in internally generated events.
main126.cc: shows how LHEF version 3.0 files can be read and used to fill several histograms of the same property, but with different event weights.
main241.cc: set up a fictitious production process to a generic resonance, where you easily can compose your own list of (two-body) decay modes to a variety of final states. Also traces decay chains down to truly stable particles: gamma, e^+-, p/pbar and neutrinos. Suitable for astroparticle applications, like neutralino pair annihilation, where cross sections are calculated separately in another program. Also shows how to plot histograms using the Pyplot solution.
main263.cc: demonstrates the use of in-situ hadronization reweighting for variations of both kinematic and flavor hadronization parameters. The output compares multiplicity distributions from the default parameters to the reweighted output with the varied parameters and the output using the varied parameters without reweighting.

MC@NLO

main151.cc: demonstrates MC@NLO matching with LHEF input from MadGraph5_aMC@NLO. Input is provided by the main151.cmnd file.

Merging

main152.cc: exemplifies an improved matching of parton showers to LHEF-style input based on the POWHEG approach. The main152.cmnd allows to switch between several different matching options. It also allows to select input process, in this case either for the POWHEG-hvq program applied to top pair production Cor10 or for QCD 2+3-jet events. The small samples of input events are stored in the powheg-hvq.lhe and powheg-dijets.lhe files, respectively.
main154.cc: demonstrates how to link the POWHEGBOX matrix element programs dynamically, bypassing the need for intermediate LHE files. Two special files are used in this option: include/Pythia8Plugins/LHAPowheg.h contains the LHAup class wrapper used to build the POWHEG plugin libraries, and include/Pythia8Plugins/PowhegProcs.h the simple class that facilitates loading the POWHEG plugins. In addition main154.cmnd contains the commands needed for POWHEGBOX to run the example.
main161.cc: exemplifies CKKW-L merging with a user-defined merging scale. Input is provided by the main161.cmnd file.
main162.cc:
main162.cc exemplifies various multi-jet merging schemes in Pythia, depending on the .cmnd input file: main162ckkwl.cmnd for CKKW-L, main162umeps.cmnd for UMEPS, main162nl3.cmnd for NL3, main162unlops.cmnd for UNLOPS, main162mess.cmnd for Vincia's CKKW-L sector merging (MESS).
main163.cc: exemplifies MLM merging, either in the ALPGEN variant or in the Madgraph one, and with input events either from ALPGEN or from Madgraph, with relevant control cards stored in main163.cmnd. See Jet Matching for further details. Traditionally the ALPGEN output is split into one file with events and another with parameters and cross sections (unlike in LHEF). Here a sample of W + 3 jets events is stored in main163.unw and the parameters to go with it in main163_unw.par. Madgraph events are taken from the w+_production_lhc_2.lhe file in this case.
main164.cc: general main program to use Pythia's matching and merging schemes. Which method is used is specified by the .cmnd input file: main164mcatnlo.cmnd for MC@NLO matching with Madgraph5_aMC@NLO, main164powheg.cmnd for POWHEG matching with POWHEG-BOX, main164ckkwl.cmnd for CKKW-L merging, main164mess.cmnd for Vincia's CKKW-L sector merging (MESS), main164umeps.cmnd for UMEPS merging, main164unlops.cmnd for UNLOPS merging, main164mlm.cmnd for MLM jet matching, main164fxfx.cmnd for FxFx merging.

MESS

main162.cc:
main162.cc exemplifies various multi-jet merging schemes in Pythia, depending on the .cmnd input file: main162ckkwl.cmnd for CKKW-L, main162umeps.cmnd for UMEPS, main162nl3.cmnd for NL3, main162unlops.cmnd for UNLOPS, main162mess.cmnd for Vincia's CKKW-L sector merging (MESS).

Minimum bias

main202.cc: compares the charged multiplicity distribution, and a few other minimum-bias physics aspects, between default PYTHIA PDF and another one. Requires that LHAPDF is properly linked.
main321.cc: tests of cross sections, multiplicities and average transverse momenta for elastic, diffractive and nondiffractive topologies, using main321.cmnd to pick processes. For photoproduction one can use the alternative main321photons.cmnd input.

MLM

main163.cc: exemplifies MLM merging, either in the ALPGEN variant or in the Madgraph one, and with input events either from ALPGEN or from Madgraph, with relevant control cards stored in main163.cmnd. See Jet Matching for further details. Traditionally the ALPGEN output is split into one file with events and another with parameters and cross sections (unlike in LHEF). Here a sample of W + 3 jets events is stored in main163.unw and the parameters to go with it in main163_unw.par. Madgraph events are taken from the w+_production_lhc_2.lhe file in this case.
main164.cc: general main program to use Pythia's matching and merging schemes. Which method is used is specified by the .cmnd input file: main164mcatnlo.cmnd for MC@NLO matching with Madgraph5_aMC@NLO, main164powheg.cmnd for POWHEG matching with POWHEG-BOX, main164ckkwl.cmnd for CKKW-L merging, main164mess.cmnd for Vincia's CKKW-L sector merging (MESS), main164umeps.cmnd for UMEPS merging, main164unlops.cmnd for UNLOPS merging, main164mlm.cmnd for MLM jet matching, main164fxfx.cmnd for FxFx merging.

MPI

main326.cc: example on how double parton scattering events can be reweighted according to a different model than default in Pythia. Contributed by Boris Blok and Paolo Gunnellini.

Multi‑instance

main324.cc: use several instances of Pythia, one for signal events and others for a variable number of pileup and "beam-gas" events, combined into one common event record. Illustrates how new Pythia instances can copy existing settings and particle data.

Multiplicities

main461.cc: compare the energy dependence of the average charged multiplicity between the simple treatment in rescattering and the full framework.

NL3

main162.cc:
main162.cc exemplifies various multi-jet merging schemes in Pythia, depending on the .cmnd input file: main162ckkwl.cmnd for CKKW-L, main162umeps.cmnd for UMEPS, main162nl3.cmnd for NL3, main162unlops.cmnd for UNLOPS, main162mess.cmnd for Vincia's CKKW-L sector merging (MESS).
main164.cc: general main program to use Pythia's matching and merging schemes. Which method is used is specified by the .cmnd input file: main164mcatnlo.cmnd for MC@NLO matching with Madgraph5_aMC@NLO, main164powheg.cmnd for POWHEG matching with POWHEG-BOX, main164ckkwl.cmnd for CKKW-L merging, main164mess.cmnd for Vincia's CKKW-L sector merging (MESS), main164umeps.cmnd for UMEPS merging, main164unlops.cmnd for UNLOPS merging, main164mlm.cmnd for MLM jet matching, main164fxfx.cmnd for FxFx merging.

NLO

main162.cc:
main162.cc exemplifies various multi-jet merging schemes in Pythia, depending on the .cmnd input file: main162ckkwl.cmnd for CKKW-L, main162umeps.cmnd for UMEPS, main162nl3.cmnd for NL3, main162unlops.cmnd for UNLOPS, main162mess.cmnd for Vincia's CKKW-L sector merging (MESS).
main164.cc: general main program to use Pythia's matching and merging schemes. Which method is used is specified by the .cmnd input file: main164mcatnlo.cmnd for MC@NLO matching with Madgraph5_aMC@NLO, main164powheg.cmnd for POWHEG matching with POWHEG-BOX, main164ckkwl.cmnd for CKKW-L merging, main164mess.cmnd for Vincia's CKKW-L sector merging (MESS), main164umeps.cmnd for UMEPS merging, main164unlops.cmnd for UNLOPS merging, main164mlm.cmnd for MLM jet matching, main164fxfx.cmnd for FxFx merging.

Onia

main243.cc: shows (a) how to use UserHooks to regularize onium cross section for pT → 0, and (b) how decays could be handled externally.
main363.cc: demonstrates how to generate quarkonia events with the external HelacOnia package interfaced to Pythia, and compare results with the internal implementation.
main365.cc: calculates the inclusive branching fractions for the Standard Model Higgs into quarkonia using the LETO timelike parton shower.

OpenMP

main224.cc: allows to steer Pythia from the command line, can produce HepMC files, and allows for OpenMP parallelization. More documentation can be obtained by executing ./main224 --help. The input file main224.cmnd further illustrates the use of DIRE.
main402.cc: comparison of VINCIA and Pythia on inclusive jets at LHC, with option to run the two generators in parallel using OpenMP. See main204.cc for how to do this with the Parallelism framework.

Optimization

main424.cc: variable beam energy and types for hadron-ion collisions, where the initialization can be cached for later use.

P pbar

main329.cc: comparison of charged multiplicity distributions with data at 200 (UA5), 900 (UA5) and 1800 (E735) GeV.

Parallelism

main221.cc: gives an example of PythiaParallelism usage. This program is equivalent to main101.cc, but does event generation in parallel.
main222.cc: equivalent to main221.cc, but is much more heavily commented to give more in-depth explanations of how the code works.
main223.cc: perform analyses in parallel using the Parallelism:processAsync setting.
main263.cc: demonstrates the use of in-situ hadronization reweighting for variations of both kinematic and flavor hadronization parameters. The output compares multiplicity distributions from the default parameters to the reweighted output with the varied parameters and the output using the varied parameters without reweighting.
main292.py: a Python interface equivalent to main222.cc. Provides an example of how to derive PYTHIA classes in Python.
main404.cc: demonstrates the example of main201 using the Parallelism framework.

Partial cross sections

main296.py: Python script studying total cross sections that accesses Pythia via the simple C++ Pythia wrapper class main296Lib.cc. This wrapper module must be compiled with make libmain296Lib.so.
main328.cc: study total, elastic and diffractive cross sections in several models (SaS/DL; MBR, ABMST, RPP2016) as a function of collision energy.
main486.cc: study total and inelastic cross section for various beam combinations, using the public methods in the Pythia class. These methods are intended for fast switching, and only provide the SaS/DL ansats at high energies.

Particle data

main294.py: standalone Python code that parses the XML particle database and displays data for a requested particle.

Parton distribution

main201.cc: a test of the shape of parton densities, as a check prior to using a given PDF set in a generator. Requires that LHAPDF is properly linked. Also shows how to plot histograms (with logarithmic x scale) using the Pyplot solution.
main202.cc: compares the charged multiplicity distribution, and a few other minimum-bias physics aspects, between default PYTHIA PDF and another one. Requires that LHAPDF is properly linked.
main203.cc: compares the internal and LHAPDF implementations of the NNPDF 2.3 QCD+QED sets, for results and for timing. Requires that LHAPDF is properly linked.
main204.cc: tests the possibility to do backwards evolution from an incoming photon at the hard interaction. Input in main204.cmnd and photoninproton.lhe. Requires that you link to a LHAPDF set that includes the photon PDF.
main245.cc: shows how to write external classes, derived from PYTHIA base classes, that can be handed to PYTHIA for internal generation. The MIXMAX random number generator is this way compared with the default PYTHIA one. Explicit implementations are included for the generation of external beam momentum spread and vertex location, and for a simple scaling external parton distribution set.
main506.cc: exemplifies how you can use the internal implementation of interpolation in an lhagrid1.dat file, without linking LHAPDF6. Also illustrates the topical issue of associated event properties for an intermediate spinless resonance in γ + γ → γ + γ at 750 GeV.

PDFs

main481.cc: plot PDFs for a large number of hadrons.

Performance

main247.cc: illustrates the use of UserHooks to veto events after hadronization, but before any subsequent processes such as rescattering or Bose-Einstein.

Photon beam

main204.cc: tests the possibility to do backwards evolution from an incoming photon at the hard interaction. Input in main204.cmnd and photoninproton.lhe. Requires that you link to a LHAPDF set that includes the photon PDF.
main343.cc: exemplifies how to generate all relevant contributions for charged particle spectra in photon-photon and photon-proton collisions.
main344.cc: exemplifies how to provide an external photon flux for photo-production processes.
main345.cc: demonstrates how to generate different types of photon-initiated dilepton events in proton-proton collisions.
main506.cc: exemplifies how you can use the internal implementation of interpolation in an lhagrid1.dat file, without linking LHAPDF6. Also illustrates the topical issue of associated event properties for an intermediate spinless resonance in γ + γ → γ + γ at 750 GeV.

Photon‑photon

main343.cc: exemplifies how to generate all relevant contributions for charged particle spectra in photon-photon and photon-proton collisions.

Photoproduction

main342.cc: exemplifies hard diffraction in the context of a photon-inside-lepton beam, like at HERA.
main343.cc: exemplifies how to generate all relevant contributions for charged particle spectra in photon-photon and photon-proton collisions.
main344.cc: exemplifies how to provide an external photon flux for photo-production processes.
main345.cc: demonstrates how to generate different types of photon-initiated dilepton events in proton-proton collisions.

Pileup

main324.cc: use several instances of Pythia, one for signal events and others for a variable number of pileup and "beam-gas" events, combined into one common event record. Illustrates how new Pythia instances can copy existing settings and particle data.

Powheg

main152.cc: exemplifies an improved matching of parton showers to LHEF-style input based on the POWHEG approach. The main152.cmnd allows to switch between several different matching options. It also allows to select input process, in this case either for the POWHEG-hvq program applied to top pair production Cor10 or for QCD 2+3-jet events. The small samples of input events are stored in the powheg-hvq.lhe and powheg-dijets.lhe files, respectively.
main154.cc: demonstrates how to link the POWHEGBOX matrix element programs dynamically, bypassing the need for intermediate LHE files. Two special files are used in this option: include/Pythia8Plugins/LHAPowheg.h contains the LHAup class wrapper used to build the POWHEG plugin libraries, and include/Pythia8Plugins/PowhegProcs.h the simple class that facilitates loading the POWHEG plugins. In addition main154.cmnd contains the commands needed for POWHEGBOX to run the example.
main164.cc: general main program to use Pythia's matching and merging schemes. Which method is used is specified by the .cmnd input file: main164mcatnlo.cmnd for MC@NLO matching with Madgraph5_aMC@NLO, main164powheg.cmnd for POWHEG matching with POWHEG-BOX, main164ckkwl.cmnd for CKKW-L merging, main164mess.cmnd for Vincia's CKKW-L sector merging (MESS), main164umeps.cmnd for UMEPS merging, main164unlops.cmnd for UNLOPS merging, main164mlm.cmnd for MLM jet matching, main164fxfx.cmnd for FxFx merging.

Process cross sections

main282.cc: a systematic comparison of several cross section values with their corresponding values in PYTHIA 6.4, the latter available as a table in the code.

Process selection

main113.cc: a simple study of several different kinds of events, with the choice to be made in the main113.cmnd "cards file". Also shows how to plot histograms using the Pyplot approach.

Process veto

main242.cc: illustration how UserHooks can be used interact directly with the event-generation process.
main293.py: a Python interface equivalent to main242.cc. Demonstrates usage of a PYTHIA plugin within the Python interface.

Proton‑ion

main422.cc: p-Pb collisions at LHC energies, using the Angantyr model for Heavy Ion collisions, and analyzing events by centrality bins.

pT bias

main322.cc: generation of the QCD jet cross section biased towards higher pT values, by two different techniques. Firstly, by splitting the run into subruns, each in its own pT bin, and adding the results properly reweighted. Two suboptions, with limits set either in the main program or by subrun specification in the main322.cmnd file. Secondly, by a continuous reweighting with a pT^4 bias in the selection, compensated by a 1/pT^4 event weight. Also inclusion of soft processes is illustrated, with subruns and weighted events.

pT spectra

main462.cc: compare multiplicities and pT spectra with or without rescattering, the former with or without rescattering between nearest neighbours along the string.

Pythia 6

main233.cc: example how to create a tailor-made copy of the ordinary event record, here with hard-process history tracing closer to the PYTHIA 6 conventions.
main282.cc: a systematic comparison of several cross section values with their corresponding values in PYTHIA 6.4, the latter available as a table in the code.

Python

main241.cc: set up a fictitious production process to a generic resonance, where you easily can compose your own list of (two-body) decay modes to a variety of final states. Also traces decay chains down to truly stable particles: gamma, e^+-, p/pbar and neutrinos. Suitable for astroparticle applications, like neutralino pair annihilation, where cross sections are calculated separately in another program. Also shows how to plot histograms using the Pyplot solution.
main291.py: a Python interface equivalent to main101.cc, i.e. a minimal example.
main292.py: a Python interface equivalent to main222.cc. Provides an example of how to derive PYTHIA classes in Python.
main293.py: a Python interface equivalent to main242.cc. Demonstrates usage of a PYTHIA plugin within the Python interface.
main294.py: standalone Python code that parses the XML particle database and displays data for a requested particle.
main295.py: a Python interface equivalent to main154.cc, with interface to Madgraph.
main296.py: Python script studying total cross sections that accesses Pythia via the simple C++ Pythia wrapper class main296Lib.cc. This wrapper module must be compiled with make libmain296Lib.so.

R‑hadron

main505.cc: production of long-lived R-hadrons, that are forced to decay at separate vertices and possibly with changed momenta.

R‑hadrons

main367.cc: presents a fictitious scenario where the top is long-lived enough to hadronize. This is studied using the R-hadron machinery, in e^+e^- or pp collisions.

Random number generator

main245.cc: shows how to write external classes, derived from PYTHIA base classes, that can be handed to PYTHIA for internal generation. The MIXMAX random number generator is this way compared with the default PYTHIA one. Explicit implementations are included for the generation of external beam momentum spread and vertex location, and for a simple scaling external parton distribution set.

Rescattering

main461.cc: compare the energy dependence of the average charged multiplicity between the simple treatment in rescattering and the full framework.
main462.cc: compare multiplicities and pT spectra with or without rescattering, the former with or without rescattering between nearest neighbours along the string.
main464.cc: plot the energy dependence of the low-energy cross sections used in the hadronic rescattering framework.
main465.cc: plot the energy dependence of the low-energy cross sections, specifically the contribution from resonances.

Resonance decay

main244.cc: shows how an external resonance can be implemented as a new class derived from a PYTHIA base class, and be used in an external process, both of them handed in for generation as with normal internal classes.
main246.cc: illustrates how a user hook can be made to steer the angular distribution selection in resonance decays. The prime example would be if LHEF input, e.g. from Madgraph, contains undecayed resonances with helicity information. These would then be decayed isotropically by PYTHIA, but this example shows how one could do better. Some input in main246.cmnd.

Resonances

main465.cc: plot the energy dependence of the low-energy cross sections, specifically the contribution from resonances.
main467.cc: generate tetraquarks from the rescattering of a D0 and Dbar*0 beam.
main468.cc: generate tetraquarks from the rescattering of D0 and Dbar*0 mesons produced in LHC events.

reuse MPI initialization

main482.cc: test switching between hadron beams on an event-by-event basis. Compare running times for different scenarios.

Reweighting

main263.cc: demonstrates the use of in-situ hadronization reweighting for variations of both kinematic and flavor hadronization parameters. The output compares multiplicity distributions from the default parameters to the reweighted output with the varied parameters and the output using the varied parameters without reweighting.

Rivet

main144.cc: streamlined event generation with possibility to output ROOT files, output HepMC files and run RIVET analyses, all by specifying output modes in a cmnd file, where also the event generator settings are specified. The example is run with command line options, run ./main144 -h to see a full list. See ROOT Usage for information about ROOT output, RIVET Usage for information about RIVET and HepMC Interface for information about HepMC.
main164.cc: general main program to use Pythia's matching and merging schemes. Which method is used is specified by the .cmnd input file: main164mcatnlo.cmnd for MC@NLO matching with Madgraph5_aMC@NLO, main164powheg.cmnd for POWHEG matching with POWHEG-BOX, main164ckkwl.cmnd for CKKW-L merging, main164mess.cmnd for Vincia's CKKW-L sector merging (MESS), main164umeps.cmnd for UMEPS merging, main164unlops.cmnd for UNLOPS merging, main164mlm.cmnd for MLM jet matching, main164fxfx.cmnd for FxFx merging.
main421.cc: simple pp collisions as in main101.cc, but using the Angantyr model for Heavy Ion collisions. Also shows how Rivet analyses can be set up easily using a special interface.

Root

main141.cc: use ROOT to visualize the particles produced by Pythia in (y,phi) space.
main142.cc: use ROOT to visualize different jet algoritms in (y,phi) space. The jet clustering is done with FastJet. The produced figure was used in the article "50 years of Quantum Chromodynamics" in celebration of the 50th anniversary of QCD (EPJC).
main143.cc: shows how ROOT can be used for histogramming in a program that for the rest is structured like a normal PYTHIA run.
main144.cc: streamlined event generation with possibility to output ROOT files, output HepMC files and run RIVET analyses, all by specifying output modes in a cmnd file, where also the event generator settings are specified. The example is run with command line options, run ./main144 -h to see a full list. See ROOT Usage for information about ROOT output, RIVET Usage for information about RIVET and HepMC Interface for information about HepMC.

Rope hadronization

main442.cc: shows how flavour production is changed in the rope hadronization framework.

Second interaction

main323.cc: generation of two predetermined hard interactions in each event.

Slowjet

main211.cc: generation of QCD jet events at the LHC, with jet analysis using the SlowJet inclusive anti-kT sequential-recombination finder.
main213.cc: a comparison of SlowJet and FastJet jet finding, showing that they find the same jets if run under identical conditions, in this case for QCD jets.
main214.cc: a comparison of jet properties on the parton and the hadron level, illustrating possibilities for larger control of which particles are used in the jet analyses.

Space‑time picture

main469.cc: show as a function of time and distance, from 1 fm to 1 m, how particles are produced, decay and rescatter.

String shoving

main441.cc: shows how the string shoving mechanism, part of the rope hadronization framework, can be set up and used to generate ridge effects.

Subruns

main123.cc: a streamlined version of main122.cc, where two Les Houches Event Files (ttbar.lhe and ttbar2.lhe) successively are used as input in main123.cmnd file.

Supersymmetry

main233.cc: example how to create a tailor-made copy of the ordinary event record, here with hard-process history tracing closer to the PYTHIA 6 conventions.
main501.cc: tests of internally implemented cross sections for Supersymmetric particle production, with SUSY spectrum defined in slha2-example.spc and settings in main501.cmnd. For illustration, an alternative example spectrum is also available, sps1aWithDecays.spc, which contains a decay table in SLHA format.
main508.cc: simple setup for Dark Matter production in several different scenarios, as specified in main508.cmnd, notably with long-lived particle signatures.

Switch beam

main482.cc: test switching between hadron beams on an event-by-event basis. Compare running times for different scenarios.
main483.cc: simple example of how Pythia can be used to simulate a basic hadronic cascade in the atmosphere.
main484.cc: as main483.cc, but using the PythiaCascade class to perform the separate collisions or decays, while the bookkeeping of the cascade evolution remains in the main program.
main485.cc: an even simpler example of one collision or decay at a time, as performed in PythiaCascade.

Switch collision energy

main482.cc: test switching between hadron beams on an event-by-event basis. Compare running times for different scenarios.
main483.cc: simple example of how Pythia can be used to simulate a basic hadronic cascade in the atmosphere.
main484.cc: as main483.cc, but using the PythiaCascade class to perform the separate collisions or decays, while the bookkeeping of the cascade evolution remains in the main program.
main485.cc: an even simpler example of one collision or decay at a time, as performed in PythiaCascade.

Tevatron

main102.cc: a simple study of the pT spectrum of Z bosons at the Tevatron.
main112.cc: a simple study of the pT spectrum of Z bosons at the Tevatron, with Pyplot option for displaying the result, but otherwise equivalent with main102.cc.

Thermal model

main443.cc: study particle composition in the thermal/exponential model for flavour production, compared with the standard tunneling/Gaussian ansatz.

Top

main367.cc: presents a fictitious scenario where the top is long-lived enough to hadronize. This is studied using the R-hadron machinery, in e^+e^- or pp collisions.
main403.cc: VINCIA setup for ttbar production at LHC, with measurement of run time and options to switch various shower and MPI/hadronization components on/off via command file.

Top mass

main362.cc: colour reconnection models studied for top production. Illustrates how to set up the user hooks in include/Pythia8Plugins/ColourReconnectionHooks.h, with several models not found in the standard PYTHIA library.

Total cross section

main296.py: Python script studying total cross sections that accesses Pythia via the simple C++ Pythia wrapper class main296Lib.cc. This wrapper module must be compiled with make libmain296Lib.so.
main328.cc: study total, elastic and diffractive cross sections in several models (SaS/DL; MBR, ABMST, RPP2016) as a function of collision energy.
main486.cc: study total and inelastic cross section for various beam combinations, using the public methods in the Pythia class. These methods are intended for fast switching, and only provide the SaS/DL ansats at high energies.

Tuning

main144.cc: streamlined event generation with possibility to output ROOT files, output HepMC files and run RIVET analyses, all by specifying output modes in a cmnd file, where also the event generator settings are specified. The example is run with command line options, run ./main144 -h to see a full list. See ROOT Usage for information about ROOT output, RIVET Usage for information about RIVET and HepMC Interface for information about HepMC.
main202.cc: compares the charged multiplicity distribution, and a few other minimum-bias physics aspects, between default PYTHIA PDF and another one. Requires that LHAPDF is properly linked.
main262.cc: set up automatic uncertainty band variations to PDFs and factorization and renormalization scales.
main263.cc: demonstrates the use of in-situ hadronization reweighting for variations of both kinematic and flavor hadronization parameters. The output compares multiplicity distributions from the default parameters to the reweighted output with the varied parameters and the output using the varied parameters without reweighting.

Two‑body decay

main241.cc: set up a fictitious production process to a generic resonance, where you easily can compose your own list of (two-body) decay modes to a variety of final states. Also traces decay chains down to truly stable particles: gamma, e^+-, p/pbar and neutrinos. Suitable for astroparticle applications, like neutralino pair annihilation, where cross sections are calculated separately in another program. Also shows how to plot histograms using the Pyplot solution.

UMEPS

main162.cc:
main162.cc exemplifies various multi-jet merging schemes in Pythia, depending on the .cmnd input file: main162ckkwl.cmnd for CKKW-L, main162umeps.cmnd for UMEPS, main162nl3.cmnd for NL3, main162unlops.cmnd for UNLOPS, main162mess.cmnd for Vincia's CKKW-L sector merging (MESS).
main164.cc: general main program to use Pythia's matching and merging schemes. Which method is used is specified by the .cmnd input file: main164mcatnlo.cmnd for MC@NLO matching with Madgraph5_aMC@NLO, main164powheg.cmnd for POWHEG matching with POWHEG-BOX, main164ckkwl.cmnd for CKKW-L merging, main164mess.cmnd for Vincia's CKKW-L sector merging (MESS), main164umeps.cmnd for UMEPS merging, main164unlops.cmnd for UNLOPS merging, main164mlm.cmnd for MLM jet matching, main164fxfx.cmnd for FxFx merging.

Uncertainty bands

main262.cc: set up automatic uncertainty band variations to PDFs and factorization and renormalization scales.

UNLOPS

main162.cc:
main162.cc exemplifies various multi-jet merging schemes in Pythia, depending on the .cmnd input file: main162ckkwl.cmnd for CKKW-L, main162umeps.cmnd for UMEPS, main162nl3.cmnd for NL3, main162unlops.cmnd for UNLOPS, main162mess.cmnd for Vincia's CKKW-L sector merging (MESS).
main164.cc: general main program to use Pythia's matching and merging schemes. Which method is used is specified by the .cmnd input file: main164mcatnlo.cmnd for MC@NLO matching with Madgraph5_aMC@NLO, main164powheg.cmnd for POWHEG matching with POWHEG-BOX, main164ckkwl.cmnd for CKKW-L merging, main164mess.cmnd for Vincia's CKKW-L sector merging (MESS), main164umeps.cmnd for UMEPS merging, main164unlops.cmnd for UNLOPS merging, main164mlm.cmnd for MLM jet matching, main164fxfx.cmnd for FxFx merging.

UPC

main344.cc: exemplifies how to provide an external photon flux for photo-production processes.
main345.cc: demonstrates how to generate different types of photon-initiated dilepton events in proton-proton collisions.

User hook

main248.cc: shows how to use a filter to select a specific final state from resonance decays.

Userhooks

main164.cc: general main program to use Pythia's matching and merging schemes. Which method is used is specified by the .cmnd input file: main164mcatnlo.cmnd for MC@NLO matching with Madgraph5_aMC@NLO, main164powheg.cmnd for POWHEG matching with POWHEG-BOX, main164ckkwl.cmnd for CKKW-L merging, main164mess.cmnd for Vincia's CKKW-L sector merging (MESS), main164umeps.cmnd for UMEPS merging, main164unlops.cmnd for UNLOPS merging, main164mlm.cmnd for MLM jet matching, main164fxfx.cmnd for FxFx merging.
main242.cc: illustration how UserHooks can be used interact directly with the event-generation process.
main243.cc: shows (a) how to use UserHooks to regularize onium cross section for pT → 0, and (b) how decays could be handled externally.
main246.cc: illustrates how a user hook can be made to steer the angular distribution selection in resonance decays. The prime example would be if LHEF input, e.g. from Madgraph, contains undecayed resonances with helicity information. These would then be decayed isotropically by PYTHIA, but this example shows how one could do better. Some input in main246.cmnd.
main247.cc: illustrates the use of UserHooks to veto events after hadronization, but before any subsequent processes such as rescattering or Bose-Einstein.
main261.cc: exemplifies how rare emissions can be enhanced in the shower.
main293.py: a Python interface equivalent to main242.cc. Demonstrates usage of a PYTHIA plugin within the Python interface.

Utility

main281.cc: shows different ways to print out and read back in settings and particle data. Useful notably for permanent updates of the latter.

Vertex spread

main245.cc: shows how to write external classes, derived from PYTHIA base classes, that can be handed to PYTHIA for internal generation. The MIXMAX random number generator is this way compared with the default PYTHIA one. Explicit implementations are included for the generation of external beam momentum spread and vertex location, and for a simple scaling external parton distribution set.

Vincia

main224.cc: allows to steer Pythia from the command line, can produce HepMC files, and allows for OpenMP parallelization. More documentation can be obtained by executing ./main224 --help. The input file main224.cmnd further illustrates the use of DIRE.
main401.cc: simple example of the VINCIA (or DIRE) shower model(s), on Z decays at LEP I, with some basic event shapes, spectra, and multiplicity counts.
main402.cc: comparison of VINCIA and Pythia on inclusive jets at LHC, with option to run the two generators in parallel using OpenMP. See main204.cc for how to do this with the Parallelism framework.
main403.cc: VINCIA setup for ttbar production at LHC, with measurement of run time and options to switch various shower and MPI/hadronization components on/off via command file.
main404.cc: demonstrates the example of main201 using the Parallelism framework.
main405.cc: VINCIA setup for electroweak shower off a fictitious process for Z decay to neutrinos at high mass. (In the absence of a weak shower, these would not shower at all.) The VINCIA EW shower requires hard-process partons with assigned helicities. This is done via Pythia's MG5 matrix-element interface, which must be compiled and linked (using configure --with-mg5mes).
main406.cc: previously main203.cc VINCIA setup for electroweak shower off high-pT dijets at the LHC. The VINCIA EW shower requires hard-process partons with assigned helicities. This is done via Pythia's MG5 matrix-element interface, which must be compiled and linked (using configure --with-mg5mes).
main407.cc: VINCIA electroweak showers off an LHEF file for dark-matter annihilation. The VINCIA EW shower requires hard-process partons with assigned helicities. In this example, these are read in from the LHEF file.

Weak showers

main405.cc: VINCIA setup for electroweak shower off a fictitious process for Z decay to neutrinos at high mass. (In the absence of a weak shower, these would not shower at all.) The VINCIA EW shower requires hard-process partons with assigned helicities. This is done via Pythia's MG5 matrix-element interface, which must be compiled and linked (using configure --with-mg5mes).
main406.cc: previously main203.cc VINCIA setup for electroweak shower off high-pT dijets at the LHC. The VINCIA EW shower requires hard-process partons with assigned helicities. This is done via Pythia's MG5 matrix-element interface, which must be compiled and linked (using configure --with-mg5mes).
main407.cc: VINCIA electroweak showers off an LHEF file for dark-matter annihilation. The VINCIA EW shower requires hard-process partons with assigned helicities. In this example, these are read in from the LHEF file.

Z production

main102.cc: a simple study of the pT spectrum of Z bosons at the Tevatron.
main112.cc: a simple study of the pT spectrum of Z bosons at the Tevatron, with Pyplot option for displaying the result, but otherwise equivalent with main102.cc.
main325.cc: exemplifies the generation of hard diffractive processes.