EvtGenDecays Class Reference

A class to perform decays via the external EvtGen decay program, see http://evtgen.warwick.ac.uk/, the program manual provided with the EvtGen distribution, and D. More...

#include <EvtGenDecays.h>

Collaboration diagram for EvtGenDecays:

Classes
struct	Signal
	Map of signal particle info. More...

Public Member Functions
	EvtGenDecays (Pythia8::Pythia *pythiaPtrIn, EvtGen *evtGen, bool limit=true)
	Expert constructor which takes an already initialized EvtGen instance.
	EvtGenDecays (Pythia8::Pythia *pythiaPtrIn, std::string decayFile, std::string particleDataFile, EvtExternalGenList *extPtrIn=0, EvtAbsRadCorr *fsrPtrIn=0, int mixing=1, bool xml=false, bool limit=true, bool extUse=true, bool fsrUse=true)
	Constructor.
	~EvtGenDecays ()
	Destructor.
	EvtGenDecays (const EvtGenDecays &)=delete
	forbid copy
EvtGenDecays &	operator= (const EvtGenDecays &)=delete
	forbid assignment
void	getDecayLimits (bool limit)
	Get the Decay limits from Pythia.
double	decay ()
	Perform all decays and return the event weight.
void	exclude (int id)
	Stop EvtGen decaying a particle.
void	updatePythia ()
	Update the Pythia particle database from EvtGen.
void	updateEvtGen ()
	Update the EvtGen particle database from Pythia.
void	readDecayFile (std::string decayFile, bool xml=false)
	Read an EvtGen user decay file.

Public Attributes
bool	extOwner
	bool has external model
bool	fsrOwner
	bool has FSR model
EvtExternalGenList *	extPtr
	External model pointer.
EvtAbsRadCorr *	fsrPtr
	FSR model pointer.
std::list< EvtDecayBase * >	models
	list of model pointers
std::map< int, Signal >	signals
	signal particles and statuses
std::string	signalSuffix
	The suffix indicating an EvtGen particle or alias is signal.

Protected Member Functions
void	updateData (bool final=false)
	Update the particles to decay with EvtGen, and the selected signals.
void	updateEvent (Pythia8::Particle *pyPro, EvtParticle *egPro, std::vector< int > *pySigs=0, std::vector< EvtParticle * > *egSigs=0, std::vector< double > *bfs=0, double *wgt=0)
	Update the Pythia event record with an EvtGen decay tree.
bool	checkVertex (Pythia8::Particle *pyPro)
	Check if a particle can decay.
bool	checkSignal (Pythia8::Particle *pyPro)
	Check if a particle is signal.
bool	checkOsc (EvtParticle *egPro)
	Check if an EvtGen particle has oscillated.

Protected Attributes
Pythia8::Pythia *	pythiaPtr
	The pointer to the associated Pythia object.
EvtGenRandom	rndm
	Random number wrapper for EvtGen.
EvtGen *	evtgen
	The EvtGen object.
std::set< int >	incIds
	Set of particle IDs to include decays with EvtGen.
std::set< int >	excIds
	Set of particle IDs to exclude decays with EvtGen.
bool	updated
	Flag whether the final particle update has been performed.
std::map< int, Signal >::iterator	signal
	The selected signal iterator.
double	tau0Max
	Parameters used to check if a particle should decay (as set via Pythia). More...
double	tauMax
	the pythia parameter ParticleDecays:tauMax
double	rMax
	the pythia parameter ParticleDecays:rMax
double	xyMax
	the pythia parameter ParticleDecays:xyMax
double	zMax
	the pythia parameter ParticleDecays:zMax
bool	limitTau0
	the pythia parameter ParticleDecays:limitTau0
bool	limitTau
	the pythia parameter ParticleDecays:limitTau
bool	limitRadius
	the pythia parameter ParticleDecays:limitRadius
bool	limitCylinder
	the pythia parameter ParticleDecays:limitCylinder
bool	limitDecay
	is the decay limited

Static Protected Attributes
static constexpr int	NTRYDECAY = 1000
	Number of times to try a decay sampling (constant).

Detailed Description

A class to perform decays via the external EvtGen decay program, see http://evtgen.warwick.ac.uk/, the program manual provided with the EvtGen distribution, and D.

J. Lange, Nucl. Instrum. Meth. A462, 152 (2001) for details.

EvtGen performs a series of decays from some initial particle decay, rather than just a single decay, and so EvtGen cannot be interfaced through the standard external DecayHandler class without considerable complication. Consequently, EvtGen is called on the complete event record after all steps of Pythia are completed.

Oftentimes a specific "signal" decay is needed to occur once in an event, and all other decays performed normally. This is possible via reading in a user decay file (with readDecayFile) and creating aliased particles with names ending with signalSuffix. By default, this is "_SIGNAL". When decay() is called, all particles in the Pythia event record that are of the same types as the signal particles are collected. One is selected at random and decayed via the channel(s) defined for that aliased signal particle. All other particles are decayed normally. The weight for the event is calculated and returned.

It is also possible to specify a status needed to consider a particle as a signal candidate. This can be done by modifying the signals map, e.g. if the tau- is a signal candidate, then EvtGenDecays.signals[15].status = 201 will only only select as candidates any tau- with this status. This allows the event record to be changed before decays, so only certain particles are selected as possible signal candidates (e.g. passing kinematic requirements).

Please note that particles produced from a signal candidate decay are not searched for additional signal candidates. This means that if B0 and tau- have been designated as signal, then a tau- from a W- decay would be a signal candidate, while a tau- from a B0 decay would not. This restriction arises from the additional complexity of allowing recursive signal decays. The following statuses are used: 93 for particles decayed with EvtGen, 94 for particles oscillated with EvtGen, 95 for signal particles, and 96 for signal particles from an oscillation.

Definition at line 88 of file EvtGenDecays.h.

Member Data Documentation

tau0Max

double tau0Max

protected

Parameters used to check if a particle should decay (as set via Pythia).

http://home.thep.lu.se/Pythia/pythia82html/ParticleDecays.html the pythia parameter ParticleDecays:tau0Max

Definition at line 200 of file EvtGenDecays.h.

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

• generators/modules/fragmentation/include/EvtGenDecays.h