PYTHIA  8.303
Public Member Functions | Protected Member Functions | List of all members
ProcessLevel Class Reference

#include <ProcessLevel.h>

Inheritance diagram for ProcessLevel:

Public Member Functions

 ProcessLevel ()=default
 ~ProcessLevel ()
 Destructor to delete processes in containers. More...
bool init (bool doLHAin, SLHAinterface *slhaInterfacePtrIn, vector< SigmaProcess * > &sigmaPtrs, vector< PhaseSpace * > &phaseSpacePtrs)
 Initialization. More...
void setLHAPtr (LHAupPtr lhaUpPtrIn)
 Store or replace Les Houches pointer.
bool next (Event &process)
 Generate the next "hard" process. More...
bool nextLHAdec (Event &process)
 Special case: LHA input of resonance decay only. More...
void accumulate (bool doAccumulate=true)
 Accumulate and update statistics (after possible user veto). More...
void statistics (bool reset=false)
 Print statistics on cross sections and number of events. More...
void resetStatistics ()
 Reset statistics. More...
void findJunctions (Event &junEvent)
 Add any junctions to the process event record list. More...
void initDecays (LHAupPtr lhaUpPtrIn)
 Initialize and call resonance decays separately.
bool nextDecays (Event &process)
- Public Member Functions inherited from PhysicsBase
void initInfoPtr (Info &infoPtrIn)
 This function is called from above for physics objects used in a run. More...
virtual ~PhysicsBase ()
 Empty virtual destructor.
bool flag (string key) const
 Shorthand to read settings values.
int mode (string key) const
double parm (string key) const
string word (string key) const

Protected Member Functions

virtual void onInitInfoPtr () override
- Protected Member Functions inherited from PhysicsBase
 PhysicsBase ()
 Default constructor.
virtual void onBeginEvent ()
 This function is called in the very beginning of each Pythia::next call.
virtual void onEndEvent (Status)
virtual void onStat ()
 This function is called from the Pythia::stat() call.
void registerSubObject (PhysicsBase &pb)
 Register a sub object that should have its information in sync with this.

Additional Inherited Members

- Public Types inherited from PhysicsBase
enum  Status {
 Enumerate the different status codes the event generation can have.
- Protected Attributes inherited from PhysicsBase
InfoinfoPtr = {}
SettingssettingsPtr = {}
 Pointer to the settings database.
ParticleDataparticleDataPtr = {}
 Pointer to the particle data table.
HadronWidthshadronWidthsPtr = {}
 Pointer to the hadron widths data table.
RndmrndmPtr = {}
 Pointer to the random number generator.
CoupSMcoupSMPtr = {}
 Pointers to SM and SUSY couplings.
CoupSUSYcoupSUSYPtr = {}
BeamParticlebeamAPtr = {}
BeamParticlebeamBPtr = {}
BeamParticlebeamPomAPtr = {}
BeamParticlebeamPomBPtr = {}
BeamParticlebeamGamAPtr = {}
BeamParticlebeamGamBPtr = {}
BeamParticlebeamVMDAPtr = {}
BeamParticlebeamVMDBPtr = {}
PartonSystemspartonSystemsPtr = {}
 Pointer to information on subcollision parton locations.
SigmaTotalsigmaTotPtr = {}
 Pointer to the total/elastic/diffractive cross sections.
set< PhysicsBase * > subObjects
UserHooksPtr userHooksPtr

Detailed Description

The ProcessLevel class contains the top-level routines to generate the characteristic "hard" process of an event.

Constructor & Destructor Documentation

Destructor to delete processes in containers.


Run through list of first hard processes and delete them.

Run through list of second hard processes and delete them.

Member Function Documentation

void accumulate ( bool  doAccumulate = true)

Accumulate and update statistics (after possible user veto).

Increase number of accepted events.

Provide current generated cross section estimate.

Normally only one hard interaction. Then store info and done.

Increase counter for a second hard interaction.

Cross section estimate for second hard process.

Average impact-parameter factor.

Cross section estimate for combination of first and second process. Combine two possible ways and take average.

Store info and done.

void findJunctions ( Event junEvent)

Add any junctions to the process event record list.

Add any junctions to the process event record list. Also check that do not doublebook if called repeatedly.

Check all hard vertices for BNV

Ignore colorless particles and stages before hard-scattering final state.

Check baryon number of vertex.

Loop over mothers (enter with crossed colors and negative sign).

If unmatched (so far), add end. Else erase matching parton.

Loop over sisters.

If unmatched (so far), add end. Else erase matching parton.

Skip if baryon number conserved in this vertex.

Check and skip any junctions that have already been added.

Remove the tags corresponding to each of the 3 existing junction legs.

Skip if no junction colors remain.

If baryon number violated, is B = +1 or -1 (larger values not handled).

From now on, use colJun as shorthand for colVertex or acolVertex.

Order so incoming tags appear first in colVec, outgoing tags last.

Step across final-state gluons (if they come from ISR => kindJun += 2)

Check for matching initial-state (anti)colour

Step across final-state gluon

Check for infinite loop

Add junction with these tags.

Check if any junction colour lines appear both as incoming and outgoing E.g. MadGraph writes out 501 + 502 -> -503 -> 501 + 502. Repaint such cases so that the outgoing tags are different from the incoming ones.

Only consider junction-antijunction combinations

Check if all tags same

Decide which junction to repaint the final-state legs of (If both are types 3-4, arbitrarily decide to repaint iJun)

Find the corresponding decay vertex: repaint daughters recursively

Find a resonance with the right colour

Check if colour is conserved in decay

Encode new colour tag so last digit remains the same (That way, new CR type models would still allow reconnection)

Count up used colour tags until we reach colNew

Done (we found the right BNV vertex and acted recursively)

bool init ( bool  doLHAin,
SLHAinterface slhaInterfacePtrIn,
vector< SigmaProcess * > &  sigmaPtrs,
vector< PhaseSpace * > &  phaseSpacePtrs 


Main routine to initialize generation process.

Store other input pointers.

Reference to Settings.

Check whether photon inside lepton and save the mode.

initialize gammaKinematics when relevant.

Send on some input pointers.

Set up SigmaTotal. Store sigma_nondiffractive for future use.

Options to allow second hard interaction and resonance decays.

Check whether ISR or MPI applied. Affects processes with photon beams.

Second interaction not to be combined with biased phase space.

Mass and pT cuts for two hard processes.

Check whether mass and pT ranges agree or overlap.

Set up containers for all the internal hard processes.

Append containers for external hard processes, if any.

Append single container for Les Houches processes, if any.

Store location of this container, and send in LHA pointer.

If no processes found then refuse to do anything.

Check whether pT-based weighting in 2 -> 2 is requested.

Check that SUSY couplings were indeed initialized where necessary.

If SUSY processes requested but no SUSY couplings present

Fill SLHA blocks SMINPUTS and MASS from PYTHIA SM parameter values.

Initialize each process.

Sum maxima for Monte Carlo choice.

Option to pick a second hard interaction: repeat as above.

Check whether to create event weight from components.

Printout during initialization is optional.

Construct string with incoming beams and for cm energy.

Print initialization information: header.

Loop over existing processes: print individual process info.

Loop over second hard processes, if any, and repeat as above.

Listing finished.

If sum of maxima vanishes then refuse to do anything.

If two hard processes then check whether some (but not all) agree.

Check for each first process if matched in second.

Check for each second process if matched in first.

Concluding classification, including cuts.


bool next ( Event process)

Generate the next "hard" process.

Main routine to generate the hard process.

Generate the next event with two or one hard interactions.

Check that colour assignments make sense.


bool nextLHAdec ( Event process)

Special case: LHA input of resonance decay only.

Generate (= read in) LHA input of resonance decay only.

Read resonance decays from LHA interface.

Store LHA output in standard event record format.


virtual void onInitInfoPtr ( )

If an object needs to set up infoPtr for sub objects, override this and call registerSubObject for each object in question.

Reimplemented from PhysicsBase.

void resetStatistics ( )

Reset statistics.

Reset statistics on cross sections and number of events.

void statistics ( bool  reset = false)

Print statistics on cross sections and number of events.

Special processing if two hard interactions selected.


Reset sum counters.

Reset process maps.

Loop over existing processes.

Read info for process. Sum counters.

Skip Les Houches containers.

Internal process info.

Print internal process info.

Print Les Houches process info.

Print subdivision by user code for Les Houches process.

Print summed process info.

Listing finished.

Optionally reset statistics contants.

The documentation for this class was generated from the following files: