Sample Main Programs

Descriptions of available classes, methods and settings are all very good and useful. Ultimately they are necessary for you to be able to fine-tune your runs to the task at hand. To get going, however, nothing helps like having explicit examples to study. This is what is provided in the examples subdirectory, along with instructions how they should be run:

main01.cc : a simple study of the charged multiplicity for jet events at the LHC. (Brief example fitting on one slide.)
main02.cc : a simple study of the pT spectrum of Z bosons at the Tevatron. (Brief example fitting on one slide.)
main03.cc : a simple single-particle analysis of jet events, where input is set by main03.cmnd "cards file".
main04.cc : a simple study of several different kinds of events, with the choice to be made in the main04.cmnd "cards file".
main05.cc : generation of QCD jet events at the LHC, with jet analysis using the CellJet cone-jet finder.
main06.cc : tests of cross sections for elastic and diffractive topologies, using main06.cmnd to pick process.
main07.cc : tests of cross sections for minimum-bias events, using main07.cmnd to pick options.
main08.cc : generation of the QCD jet cross section by splitting the run into subruns, each in its own pT bin, and adding the results properly reweighted. Two options, with limits set either in the main program or by subrun specification in the main08.cmnd file.
main09.cc : generation of LEP1 hadronic events, i.e. e^+e^- -> gamma*/Z^0 -> q qbar, with charged multiplicity, sphericity, thrust and jet analysis.
main10.cc : illustration how userHooks can be used interact directly with the event-generation process.
main11.cc : generation of two predetermined hard interactions in each event.
main12.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.
main13.cc : a more sophisticated variant of main12.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.
main14.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.
main15.cc : loop over several tries, either to redo B decays only or to redo the complete hadronization chain of an event. Since much of the generation process is only made once this is a way to increase efficiency.
main16.cc : put all user analysis code into a class of its own, separate from the main program; provide the "cards file" name as a command-line argument.
main17.cc : collect the Pythia calls in a wrapper class, thereby simplifying the main program; provide the "cards file" name as a command-line argument.
main18.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.
main19.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.
main20.cc : shows how PYTHIA 8 can write a Les Houches Event File, using facilities potentially useful also for other programs to write an LHEF.
main21.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.
main22.cc : tests of internally implemented cross sections for Supersymmetric particle production, with SYSY spectrum defined in sps1a.spc and settings in main22.cmnd.
main23.cc : shows how an external decay handler can be linked to handle the decays of some particles.
main24.cc : shows how an external random number generator can be linked to replace the internal one.
main25.cc : shows how an external process can be implemented as a new class derived from a PYTHIA base class, and then handed in for generation as with a normal internal process.
main26.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 which are then handed in for generation as with a normal internal resonance and process.
main27.cc : shows how an external beam momentum spread and vertex location generator can be implemented as a new class derived from a PYTHIA base class, and then handed in for internal use.
main28.cc : test program for processes in scenarios with large extra dimensions or unparticles.
main29.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.
main31.cc : similar to main01, except that the event record is output in the HepMC event record format. Requires that HepMC is properly linked.
main32.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. main32.cmnd) and output HepMC event file are to be provided as command-line arguments. Requires that HepMC is properly linked.
main41.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.
main42.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.
main43.cc : tests the possibility to do backwards evolution from an incoming photon at the hard interaction. Requires that you link to a LHAPDF set that includes the photon PDF.
main44.cc : exemplifies how you create your own PDF set and link it in for use in the process generation.
main51.cc : exemplifies how you can link in runtime generation of hard processes from PYTHIA 6, using the Les Houches Accord facilities. This example is deprecated, since PYTHIA 8 by now contains essentially all hard processes found in PYTHIA 6.
main61.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.