Sample Main Programs

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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:

main00.cc : does not exist, but it has been defined in the Makefile, so this name could be used for a simple first test run.
main01.cc : a simple study of the charged multiplicity for jet events at the LHC. (Brief example fitting on one slide.)
main01.py : a Python interface equivalent of main01.cc.
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 study of several different kinds of events, with the choice to be made in the main03.cmnd "cards file".
main04.cc : tests of cross sections, multiplicities and average transverse momenta for elastic, diffractive and nondiffractive topologies, using main04.cmnd to pick processes.
main05.cc : generation of QCD jet events at the LHC, with jet analysis using the SlowJet inclusive anti-kT sequential-recombination finder and the CellJet cone-jet finder.
main06.cc : generation of LEP1 hadronic events, i.e. e^+e^- → gamma*/Z^0 → q qbar, with charged multiplicity, sphericity, thrust and jet analysis.
main07.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.
main08.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 main08.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.
main09.cc : generation of two predetermined hard interactions in each event.
main10.cc : illustration how userHooks can be used interact directly with the event-generation process.
main10.py : a Python interface equivalent of main10.cc. Provides an example of how to derive PYTHIA classes in Python.
main11.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.
main12.cc : a more sophisticated variant of main11.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.
main13.cc : a streamlined version of main12.cc, where two Les Houches Event Files (ttbar.lhe and ttbar2.lhe) successively are used as input in main13.cmnd file.
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. Also exemplifies how Higgs mass, width and branching ratios can be set by hand.
main17.cc : shows (a) how to use UserHooks to regularize onium cross section for pT → 0, and (b) how decays could be handled externally.
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. Illustrates how new Pythia instances can copy existing settings and particle data.
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. See also main64.cc.
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. Can also be used for single-resonance decays, with showers.
main22.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.
main23.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. Also how to use an external random-number generator and an external parton distribution set.
main24.cc : tests of internally implemented cross sections for Supersymmetric particle production, with SUSY spectrum defined in cmssm.spc and settings in main24.cmnd. For illustration, an alternative example spectrum is also available, sps1aWithDecays.spc, which contains a decay table in SLHA format.
main25.cc : input RPV-SUSY events from an LHEF file that contains an SLHA spectrum inside its header. The event file, main25.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.
main26.cc : test program for processes in scenarios with large extra dimensions or unparticles.
main27.cc : production of Kaluza-Klein gamma/Z states in TeV-sized extra dimensions.
main28.cc : production of long-lived R-hadrons, that are forced to decay at a separate vertices and possibly with changed momenta.
main29.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.
main30.cc : example how to create a tailormade copy of the ordinary event record, here with hard-process history tracing closer to the PYTHIA 6 conventions.
main31.cc : exemplifies an improved matching of parton showers to LHEF-style input based on the ";?>POWHEG approach. The main31.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.
main32.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 main32.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 main32.unw and the parameters to go with it in main32_unw.par. Madgraph events are taken from the w+_production_lhc_2.lhe file in this case.
main33.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 main33.cmnd contains the commands needed for POWHEGBOX to run the example.
main34.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.
main34.py : a Python interface equivalent of main34.cc. Demonstrates usage of a PYTHIA plugin within the Python interface.
main35.cc : demonstrates how to generate quarkonia events with the external HelacOnia package interfaced to Pythia, and compare results with the internal implementation.
main37.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.
main38.cc : an extended version of main37.cc, where additionally it is shown how to extract many different kinds of LHEF version 3.0 information.
main41.cc : similar to main01, except that the event record is output in the HepMC event record format. Requires that HepMC is properly linked. Note that the hepmcout41.dat output file can become quite big; so no example is included in this distribution.
main42.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. main42.cmnd) and output HepMC event file (e.g. hepmcout42.dat) are to be provided as command-line arguments. Requires that HepMC is properly linked. Note that the HepMC output file can become quite big; so no example is included in this distribution.
main43.cc : a further extension of main42.cc, where subruns are used to process several consecutive LHEF, as in main13.cc, with information stored e.g in main43.cmnd. Other comments as for main42.cc.
main46.cc : illustrated how the ProMC library can be used to store Pythia events in a compact format.
main48.cc : demonstrates how to use the EvtGenDecays class provided by include/Pythia8Plugins/EvtGen.h to perform decays with the EvtGen package. The main48.cc header contains special instructions how to configure PYTHIA for use with EvtGen.
main51.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.
main52.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.
main53.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.
main54.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.
main55.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.
main61.cc : exemplifies the generation of hard diffractive processes.
main62.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 main62.cmnd.
main63.cc : exemplifies how a user hook can be used to enhance the rate of rare emissions in the shower.
main64.cc : examplifies how LHEF version 3 events can be written on an external file.
main65.cc : exemplifies how a user hook can set space-time vertex information.
main69.cc : examplifies how to generate all relevant contributions for charged particle spectra in photon-photon and photon-proton collisions.
main71.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.
main72.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.
main73.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.
main74.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.
main80.cc : do CKKW-L merging with a merging scale defined in kT. Input is provided by the main80.cmnd file and input LHE files. Very basic and pedagogical setup, suitable for tutorials.
main81.cc : do CKKW-L merging with a merging scale defined in kT. Input is provided by the main81.cmnd file and the three data files w+_production_lhc_0.lhe, w+_production_lhc_1.lhe and w+_production_lhc_2.lhe.
main82.cc : do CKKW-L merging with a user-defined merging scale function. Input is provided by the main82.cmnd file and the three data files w+_production_lhc_0.lhe, w+_production_lhc_1.lhe and w+_production_lhc_2.lhe.
main83.cc : as main82.cc but with an additional cut on the lowest multiplicity allowed for the reclustered state. The same input as for main82.cc can be used.
main84.cc : do CKKW-L merging with output in such a way that it can be used in subsequent RIVET analyses. Input is provided by the main84.cmnd file and the three data files w+_production_lhc_0.lhe, w+_production_lhc_1.lhe and w+_production_lhc_2.lhe.
main85.cc : do CKKW-L merging, with HepMC event output. Input settings are provided by the main85.cmnd file. This example program allows the use of input Les Houches events that are regularised with only very minimal cuts, and on which Pythia itself should enforce the more restrictive merging scale cut. The example program can be used with the input files w_production_tree_0.lhe, w_production_tree_1.lhe and w_production_tree_2.lhe.
main86.cc : do unitarised ME+PS (UMEPS) merging, with HepMC event output. Input settings are provided by the main86.cmnd file. This example program allows the consistent use of input Les Houches events that are regularised with only very minimal cuts, similar to main85.cc. The example program can be used with the input files w_production_tree_0.lhe, w_production_tree_1.lhe and w_production_tree_2.lhe. The program will produce positively and negatively weighted events. See ";?>UMEPS Merging for further details.
main87.cc : do NL³ NLO merging, with inclusive NLO input, and with HepMC event output. Input settings are provided by the main87.cmnd file. This example program allows the consistent use of input Les Houches events that are regularised with only very minimal cuts, similar to main85.cc. The example program can be used with the tree-level input files w_production_tree_0.lhe, w_production_tree_1.lhe, w_production_tree_2.lhe and the inclusive POWHEG input files w_production_powheg_0.lhe, w_production_powheg_1.lhe. The program will produce positively and negatively weighted events. See ";?>NLO Merging (NL³ section) for further details.
main88.cc : do unitarised NLO+PS (UNLOPS) merging, with inclusive NLO input, and with HepMC event output. Input settings are provided by the main88.cmnd file. This example program allows the consistent use of input Les Houches events that are regularised with only very minimal cuts, similar to main85.cc. The example program can be used with the tree-level input files w_production_tree_0.lhe, w_production_tree_1.lhe, w_production_tree_2.lhe and the inclusive POWHEG input files w_production_powheg_0.lhe, w_production_powheg_1.lhe. The program will produce positively and negatively weighted events. See ";?>NLO Merging (UNLOPS section) for further details.
main89.cc : do matching/merging according to five alternative methods, simply by choosing which .cmnd file to read: main89ckkwl.cmnd for CKKW-L, main89fxfx.cmnd for FxFx, main89mlm.cmnd for MLM, main89umeps.cmnd for UMEPS, and main89unlops.cmnd for UNLOPS.
main91.cc : shows how ROOT can be used for histogramming in a program that for the rest is structured like a normal PYTHIA run.
main92.cc : shows how PYTHIA events can be stored as ROOT trees.