Equivalent photon approximation for sampling with external photon flux. More...

#include <PartonDistributions.h>

Inheritance diagram for EPAexternal:

Public Member Functions
	EPAexternal (int idBeamIn, double m2In, PDFPtr gammaFluxPtrIn, PDFPtr gammaPDFPtrIn, Info infoPtrIn, Logger loggerPtrIn=0)
	Constructor.

void	xfUpdate (int, double x, double Q2) override
	Update PDFs. More...

double	xfFlux (int id, double x, double Q2=1.) override
	External flux and photon PDFs, and approximated flux for sampling. More...

double	xfGamma (int id, double x, double Q2) override
	Photon PDFs used for the convolution with the flux. More...

double	xfApprox (int id, double x, double Q2) override
	The approximated photon flux x*f^{gamma}(x,Q2). More...

double	intFluxApprox () override

bool	hasApproxGammaFlux () override
	This derived class use approximated flux for sampling.

double	getXmin () override
	Kinematics.

double	getXhadr () override

double	sampleXgamma (double xMinIn) override
	Sampling of the x and Q2 according to differential flux. More...

double	sampleQ2gamma (double Q2minIn) override

Public Member Functions inherited from PDF
	PDF (int idBeamIn=2212)
	Constructor.

virtual	~PDF ()
	Virtual destructor.

virtual bool	init (int, string, int, Logger *)

bool	isSetup ()
	Confirm that PDF has been set up (important for LHAPDF and H1 Pomeron).

virtual void	setBeamID (int idBeamIn)
	Switch to new beam particle identities; for similar hadrons only.

void	resetValenceContent ()
	Set valence content. More...

void	setValenceContent (int idVal1In, int idVal2In, int idVal3In)

virtual void	setExtrapolate (bool)
	Allow extrapolation beyond boundaries. This is optional.

double	xf (int id, double x, double Q2)
	Read out parton density. More...

double	xfVal (int id, double x, double Q2)
	Read out valence and sea part of parton densities. More...

double	xfSea (int id, double x, double Q2)
	Only sea part of parton densities. More...

virtual bool	insideBounds (double, double)
	Check whether x and Q2 values fall inside the fit bounds (LHAPDF6 only).

virtual double	alphaS (double)
	Access the running alpha_s of a PDF set (LHAPDF6 only).

virtual double	mQuarkPDF (int)
	Return quark masses used in the PDF fit (LHAPDF6 only).

virtual int	nMembers ()
	Return number of members of this PDF family (LHAPDF6 only).

virtual void	calcPDFEnvelope (int, double, double, int)
	Calculate PDF envelope.

virtual void	calcPDFEnvelope (pair< int, int >, pair< double, double >, double, int)

virtual PDFEnvelope	getPDFEnvelope ()

virtual double	gammaPDFxDependence (int, double)
	Approximate photon PDFs by decoupling the scale and x-dependence.

virtual double	gammaPDFRefScale (int)
	Provide the reference scale for logarithmic Q^2 evolution for photons.

virtual int	sampleGammaValFlavor (double)
	Sample the valence content for photons.

virtual double	xfIntegratedTotal (double)
	The total x-integrated PDFs. Relevant for MPIs with photon beams.

virtual double	xGamma ()
	Return the sampled value for x_gamma.

virtual void	xPom (double=-1.0)
	Keep track of pomeron momentum fraction.

virtual double	fluxQ2dependence (double)

virtual double	xfMax (int id, double x, double Q2)
	Normal PDFs unless gamma inside lepton -> an overestimate for sampling.

virtual double	xfSame (int id, double x, double Q2)
	Normal PDFs unless gamma inside lepton -> Do not sample x_gamma.

virtual void	setVMDscale (double=1.)
	Allow for new scaling factor for VMD PDFs.

bool	sSymmetric () const
	Return if s/sbar, c/cbar, and b/bbar PDFs are symmetric.

bool	cSymmetric () const

bool	bSymmetric () const

void	sSymmetric (bool sSymmetricIn)
	Set s/sbar, c/cbar, and b/bbar PDFs symmetric.

void	cSymmetric (bool cSymmetricIn)

void	bSymmetric (bool bSymmetricIn)

Additional Inherited Members
Protected Member Functions inherited from PDF
void	printErr (string loc, string errMsg, Logger *loggerPtr=nullptr)
	Small routine for error printout, depending on loggerPtr existing or not.

double	xfRaw (int id) const
	Get the raw stored value for the quark variable corresponding to the id. More...

bool	isValence (int id) const
	Check whether the specified id is a valence quark.

Protected Attributes inherited from PDF
int	idBeam
	Store relevant quantities.

int	idBeamAbs

int	idSav

int	idVal1

int	idVal2

int	idVal3

double	xSav

double	Q2Sav

double	xu
	Stored quantities.

double	xd

double	xs

double	xubar

double	xdbar

double	xsbar

double	xc

double	xb

double	xcbar

double	xbbar

double	xg

double	xlepton

double	xgamma

bool	isSet

bool	isInit

int	beamType

bool	hasGammaInLepton
	True if a photon beam inside a lepton beam, otherwise set false.

bool	sSymmetricSave = false
	Whether to treat flavoured PDFs as symmetric, for efficiency.

bool	cSymmetricSave = true

bool	bSymmetricSave = true

Detailed Description

Equivalent photon approximation for sampling with external photon flux.

Member Function Documentation

double intFluxApprox ( )

overridevirtual

Return integrated over-estimate for photon flux to approximate soft cross sections.

Check the used approximation and return the integral.

Reimplemented from PDF.

double sampleQ2gamma ( double Q2minIn )

overridevirtual

Sample the virtuality for the photon, either based on the estimate to be corrected later, or for integrated flux (accepted events) where oversampling has already been corrected.

Sample value for the intermediate photon according to the flux. If externally generated (LHE) event, use the approximation. Notice that in the former case sample from the whole phase space but in the latter start with lower limit provided as an argument.

Sample from 1./Q^2 to start with, correct for actual Q2 dependence.

Check first that a finite value obtained, then check whether value to be accepted and exit.

Check number of tries.

Reimplemented from PDF.

double sampleXgamma ( double xMinIn )

overridevirtual

Sampling of the x and Q2 according to differential flux.

Sample the x_gamma value according to given photon flux approximation.

Sample with lepton-type flux.

Sample with photon flux for nuclei.

Calculate the integrals of over estimates, either only above the cut value or with both contributions.

Select the sampling region.

Sample x value according to the selected approximation region.

Return zero for undefined cases.

Reimplemented from PDF.

double xfApprox	(	int	id,
		double	x,
		double	Q2
	)

overridevirtual

The approximated photon flux x*f^{gamma}(x,Q2).

Differential in Q2 for leptons.

Piece-wise approximation for heavy ions.

Reimplemented from PDF.

double xfFlux	(	int	id,
		double	x,
		double	Q2 = `1.`
	)

overridevirtual

External flux and photon PDFs, and approximated flux for sampling.

Accurate flux, provided externally.

The external flux, check that pointer exists.

Reimplemented from PDF.

double xfGamma	(	int	id,
		double	x,
		double	Q2
	)

overridevirtual

Photon PDFs used for the convolution with the flux.

Return xf from the photon PDF.

Reimplemented from PDF.

void xfUpdate	(	int	,
		double	x,
		double	Q2
	)

overridevirtual

Update PDFs.

Approximate the differential photon flux with alphaEM/PI/x/Q2. Derived from EPA for leptons but provides leading (small-x) behaviour for hadrons as well.

Calculate (Q2-integrated) approximation for xfGamma.

Integrated in Q2, to be used for direct process sampling.

Approximate the convolution with photon PDFs.

To preserve x/xGamma < 1.

Integrals for the overestimates.

Multiply the approximated flux with PDFs.

idSav = 9 to indicate that all flavours reset.

Implements PDF.

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

include/Pythia8/PartonDistributions.h
src/PartonDistributions.cc

Public Member Functions

Additional Inherited Members

Detailed Description

Member Function Documentation