Program Files
The code is subdivided into a set of files, mainly by physics
task. Each file typically contains one main class, but often
with a few related helper classes that are not used elsewhere in
the program. Normally the files come in pairs.
- A header file,
.h
in the include/Pythia8
subdirectory, where the public interface of the class is declared,
and inline methods are defined.
- A source code file,
.cc
in the src
subdirectory, where most of the methods are implemented.
During compilation, related dependency files, .d
, and
compiled code, .o
are created in the tmp
subdirectory.
In part the .xml
documentation files in the
xmldoc
subdirectory have matching names, but the match
is broken by the desire to group topics more by user interaction than
internal operation. On these pages the function of the different code
files is summarized. Currently, each .xml
file is also
translated into an .html
one in the
htmldoc
subdirectory, to allow easy viewing of the
contents in a web browser, and an .php
one in
phpdoc
, for more sophisticated interactivity
if that subdirectory is installed on a web server.
Here is the current list of files, ordered alphabetically, with a brief
description of contents.
file
Analysis
contains routines to analyze events. Currently it can do sphericity,
thrust, Lund/Jade/Durham jet clustering, cone-jet finding, and the
kT, anti-kT and Cambridge/Aachen algorithms for
hadron colliders.
file
Basics
contains some basic facilities of general use: a random number
generator Rndm
, a four-vector class Vec4
, and a
histogram class Hist
.
file
BeamParticle
contains information on all partons extracted from one of the two
beams. Defines modified parton distributions accordingly during the
showering and multiparton interactions processing, thereby extending on
the one-particle-inclusive distributions defined by the previous class.
Finds the internal structure for a beam remnant.
file
BeamRemnants
adds primordial kT to the set of hard subsystems,
and combines these subsystems with the two beam remnants to provide
the overall energy-momentum picture. Also ties together all the
colour lines into consistent singlets.
file
BeamShape
generates momentum spread of beams, and spread of collision vertex
position.
file
BoseEinstein
provides a simple method to impose Bose-Einstein correlations on
pairs of identical mesons.
file
ColourReconnection
implements several models that describe how the colour flow between
outgoing partons can be changed by nonperturbative effects.
file
ColourTracing
finds out how partons are colour-connected in (more or less long) chains.
file
Event
contains the event record, which basically is a vector of particles.
This file also contains the Particle
class, used by
Event
. Pythia
uses two Event
objects, one for the process-level record (process
) and
one for the complete event (event
).
file
FJcore
contains the external FJcore package, providing the coure functionality
of the FastJet jet fiding package.
file
FragmentationFlavZpT
contains the classes for describing the fragmentation steps in
flavour and in longitudinal and transverse momentum.
file
FragmentationSystems
defines some containers of parton systems, for use in
the fragmentation routines.
file
HadronLevel
turns the parton-level event above into a set of outgoing particles,
by applying string fragmentation (with special treatment for low-mass
systems) and secondary decays, and optionally Bose-Einstein corrections.
file
HadronScatter
contains the beginning of a machinery for final state hadronic
rescattering.
file
HelicityBasics
basic classes for the handling of helicities in tau lepton decays.
file
HelicityMatrixElements
helicity-dependent decay matrix elements for the tau lepton.
file
HiddenValleyFragmentation
hadronization in models with a hidden sector that contains an unbroken
SU(N), which gives confinement. The model and code is largely
derived from the normal fragmentation classes.
file
History
methods to reconstruct the imagined shower history of a
matrix-element-generated multiparton configuration, as part of
the CKKW-L matrix element merging.
file
Info
is a simple container that gives access to some information on the
nature of the current process, such as Mandelstam variables.
Also contains a small database for errors and warnings encountered
during program execution.
file
JunctionSplitting
processes a colour singlet system containing several (anti)junctions
such that it can be split into several systems each containing
(at most) one junction.
file
LesHouches
gives the possibility to feed in parton configurations for the
subsequent event generation. One base class is defined, with containers
for initialization and event information, that can be read from
Pythia
. Derived classes allow for a few different cases.
file
LHAFortran
is a header file only, for a class derived from the above LesHouches
one, to be used for runtime interfacing to Fortran programs, such as
PYTHIA 6.
file
Merging
Wpapper class to interface matrix element merging schemes with Pythia.
file
MergingHooks
intercede in the normal shower evolution to construct the relevant
Sudakov form factor suppressions as part of the CKKW-L matrix element
merging.
file
MiniStringFragmentation
performs string fragmentation in cases where the colour singlet
subsystem mass is so small that one or at most two primary hadrons
should be produced from it.
file
MultipartonInteractions
performs multiparton interactions.
file
ParticleData
contains a database of all necessary particle data (masses, names, ..)
and decay channels.
file
ParticleDecays
performs the decays of all normal unstable hadrons and leptons, i.e.
in mass up to and including b bbar systems. It is not
intended for decays of electroweak resonances, like Z^0.
file
PartonDistributions
contains parton distribution functions for the proton and electron.
Currently very simple, with only two p parametrizations
and one e ditto available, but it is possible to link in
external sets.
file
PartonLevel
turns the (hard) process above into a complete set of partons, by
adding initial- and final-state radiation, multiparton
interactions, and beam remnants.
file
PartonSystems
keeps track of which partons belong to which partonic subsystem,
i.e. one of the multiparton (semi)hard interactions with associated
showers.
file
PhaseSpace
selects a point in phase space for the hard-process generation,
optimized separately for each process to give improved Monte Carlo
efficiency.
file
ProcessContainer
packages the information on a given subprocess, combining the
phase-space selection and cross-section evaluation machineries
with some statistics information. Also sets up the list of processes
to be studied in a run.
file
ProcessLevel
handles the generation of the (hard) process that sets the character
of the event. This involves either using internally implemented
processes or linking to Les Houches information. The latter can
be by runtime interfaces or by reading in a file. This step also
includes resonance decays.
file
Pythia
is the main class, that administrates the whole event generation
process by making use of all the others classes. Objects of most
other classes reside (directly or indirectly) inside Pythia
,
so only a Pythia
object needs to be explicitly instantiated
and addressed by the user.
file
PythiaComplex
is only a .h
file, containing a typedef
for
double precision complex numbers.
file
PythiaStdlib
contains most of the Stdlib
headers used in PYTHIA 8,
with using
directives. It defines M_PI
if
this is not already done. Also a few simple inline methods:
pow2(x)
, pow3(x)
, pow4(x)
,
pow5(x)
and pow6(x)
for small integer
powers, and sqrtpos(x)
where a max(0., x)
ensures that one does not take the square root of a negative number.
The non-inlined string toLower(const string, bool trim = true)
converts a strimg to lowercase, and by default also removes initial and
trailing blanks or escape characters. It returns a new string, while the
inlined extension void toLowerRep(string, bool trim = true)
replaces the string in place. Finally the non-inlined
GammaReal(x)
gives the Gamma function value of
a real argument.
file
ResonanceDecays
decays resonances as part of the hard-process stage, in many cases
(but not all) including angular correlations between the decay products.
file
ResonanceWidths
encodes some properties of resonances, in particular the dynamic
calculation of widths.
file
RHadrons
handles the production and decay of hadrons formed by long-lived
gluinos, stops or sbottoms.
file
Settings
contains a database of all flags, modes, parameters and words that
determine the performance of the generator. Initial values are obtained
from the contents of the .xml
files, but these values can
then be changed by the user.
file
SigmaCompositeness
contains the cross sections and matrix elements for production of
some particles in compositeness scenarios, specifically excited
fermions.
file
SigmaEW
contains the cross sections and matrix elements for electroweak
processes involving photons, Z^0's and W^+-'s.
file
SigmaExtraDim
contains the cross sections and matrix elements for processes in
scenarios involving extra dimensions.
file
SigmaGeneric
contains the cross sections and matrix elements for some generic
processes, to be used as building blocks for a few BSM scenarios.
file
SigmaHiggs
contains the cross sections and matrix elements for Higgs production.
file
SigmaLeftRightSym
contains the cross sections and matrix elements for particle production
in left-right-symmetry scenarios, specifically righthanded Z
and W bosons and doubly-charged Higgs bosons.
file
SigmaLeptoquark
contains the cross sections and matrix elements for leptoquark production.
file
SigmaNewGaugeBosons
contains the cross sections and matrix elements for a Z'^0,
a W^+- and a horizontal gauge boson R^0.
file
SigmaOnia
contains the cross sections and matrix elements for charmonium and
bottomonium production.
file
SigmaProcess
contains the base class and derived classes for the evaluation of
different matrix elements. Also keeps track of allowed incoming
parton configurations and their cross sections, including parton
densities. In order to keep this file from becoming too big, actual
cross sections are found in several separate files of derived classes:
SigmaQCD
, SigmaEW
, SigmaOnia
,
SigmaHiggs
, SigmaSUSY
,
SigmaNewGaugeBosons
, SigmaLeftRightSym
,
SigmaLeptoquark
, SigmaCompositeness
,
SigmaExtraDim
and SigmaGeneric
.
file
SigmaQCD
contains the cross sections and matrix elements for soft and hard
QCD processes.
file
SigmaSUSY
contains the cross sections and matrix elements for Supersymmetric
processes.
file
SigmaTotal
contains parametrizations of total, elastic and diffractive hadronic
cross sections.
file
SLHAinterface
handles the communication between the SusyLesHouches
classes and Pythia.
file
SpaceShower
performs spacelike initial-state transverse-momentum-ordered
shower evolution.
file
StandardModel
contains the running alpha_strong, with Lambda
matching at flavour thresholds, the running alpha_em,
CKM mixing matrices, and a few other parameters such as
sin^2(theta_W).
file
StringFragmentation
performs string fragmentation of a given set of partons.
file
StringLength
calculates the string-length lambda measure for various
colour topologies, including junction ones.
file
SusyCouplings
stores the various couplings used for SUSY cross sections and
decays, as calculated from input e.g. based on the SUSY Les Houches
Accord.
file
SusyLesHouches
contains information on SUSY parameters and particle data as specified
by the SUSY Les Houches Accord.
file
SusyResonanceWidths
encodes some properties of supersymmetric resonances, similar to
what ResonanceWidths
does for other resonances.
file
TauDecays
the main routines for handling tau lepton decays with helicity
information.
file
TimeShower
performs timelike final-state transverse-momentum-ordered
shower evolution.
file
UserHooks
Provides a way for a user to study the event at a few intermediate
stages of evolution, to reject the event as a whole or to modify
its cross-section weight.
file
WeakShowerMEs
provides some matrix elements used for ME corrections of W
and Z weak gauge boson emission in both initial- and final-state
parton showers.