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.