StringEnd Class Reference

#include <StringFragmentation.h>

Public Member Functions
	StringEnd ()
	Constructor.
void	init (ParticleData *particleDataPtrIn, StringFlav *flavSelPtrIn, StringPT *pTSelPtrIn, StringZ *zSelPtrIn, Settings &settings)
	Save pointers.
void	setUp (bool fromPosIn, int iEndIn, int idOldIn, int iMaxIn, double pxIn, double pyIn, double GammaIn, double xPosIn, double xNegIn, int colIn)
	Set up initial endpoint values from input. More...
void	newHadron (double kappaRatio, bool forbidPopcornNow=false, bool allowPop=true, double strangeFac=0., double probQQmod=1.)
	Fragment off one hadron from the string system, in flavour and pT. More...
void	pearlHadron (StringSystem &system, int idPearlIn, Vec4 pPearlIn)
	Creation of pearl hadron. More...
Vec4	kinematicsHadron (StringSystem &system, StringVertex &newVertex, bool useInputZ=false, double zHadIn=0., bool pearlIn=false, Vec4 pPearlIn={0., 0., 0., 0.})
Vec4	kinematicsHadronTmp (StringSystem system, Vec4 pRem, double phi, double mult)
void	update ()
	Update string end information after a hadron has been removed.
void	storePrev ()
	Store old string end information.
void	updateToPrev ()
	Update string end information to previous string break.

Public Attributes
ParticleData *	particleDataPtr
	Pointer to the particle data table.
StringFlav *	flavSelPtr
	Pointers to classes for flavour, pT and z generation.
StringPT *	pTSelPtr
StringZ *	zSelPtr
StringFlav	flavSelNow
	Local copy of flavSelPtr for modified flavour selection.
bool	fromPos
	Data members.
bool	thermalModel
bool	mT2suppression
bool	closePacking
int	iEnd
int	iMax
int	idHad
int	iPosOld
int	iNegOld
int	iPosNew
int	iNegNew
int	hadSoFar
int	colOld
int	colNew
double	pxOld
double	pyOld
double	pxNew
double	pyNew
double	pxHad
double	pyHad
double	mHad
double	mT2Had
double	zHad
double	GammaOld
double	GammaNew
double	xPosOld
double	xPosNew
double	xPosHad
double	xNegOld
double	xNegNew
double	xNegHad
double	aLund
double	bLund
int	iPosOldPrev
int	iNegOldPrev
int	colOldPrev
double	pxOldPrev
double	pyOldPrev
double	GammaOldPrev
double	xPosOldPrev
double	xNegOldPrev
FlavContainer	flavOld
FlavContainer	flavNew
FlavContainer	flavOldPrev
Vec4	pHad
Vec4	pSoFar

Static Public Attributes
static const double	TINY = 1e-6
	Constants: could only be changed in the code itself. More...
static const double	PT2SAME = 0.01
	Assume two (eX, eY) regions are related if pT2 differs by less.
static const double	MEANMMIN = 0.2
static const double	MEANM = 0.8
static const double	MEANPT = 0.4

Detailed Description

The StringEnd class contains the information related to one of the current endpoints of the string system. Only to be used inside StringFragmentation, so no private members.

Member Function Documentation

Vec4 kinematicsHadron	(	StringSystem &	system,
		StringVertex &	newVertex,
		bool	useInputZ = false,
		double	zHadIn = 0.,
		bool	pearlIn = false,
		Vec4	pPearlIn = { 0., 0., 0., 0.}
	)

Fragment off one hadron from the string system, in momentum space, by taking steps either from positive or from negative end.

Fragment off one hadron from the string system, in momentum space, by taking steps from positive end.

Ensure pearl momentum is not used if pearlIn = false.

Pick fragmentation step z and calculate new Gamma.

Set up references that are direction-neutral; ...Dir for direction of iteration and ...Inv for its inverse.

Start search for new breakup in the old region.

Each step corresponds to trying a new string region.

Referance to current string region.

Now begin special section for rapid processing of low region.

A first step within a low region is easy.

Translate into x coordinates.

Store breakup vertex information from the fragmentation process.

Find and return four-momentum of the produced particle.

A first step out of a low region also OK, if there are more regions. Negative energy signals failure, i.e. in last region.

Momentum taken by stepping out of region. Continue to next region.

Else, for first step, take into account starting pT.

Now begin normal treatment of nontrivial regions. Set up four-vectors in a region not visited before.

If new region is vanishingly small, continue immediately to next. Negative energy signals failure to do this, i.e. moved too low.

Reexpress pTNew w.r.t. base vectors in new region, if possible. Recall minus sign from normalization e_x^2 = e_y^2 = -1.

Four-momentum taken so far, including new pT.

Derive coefficients for m2 expression. cM2 * x+ + cM3 * x- + cM4 * x+ * x- = m^2 - cM1;

Derive coefficients for Gamma expression. cGam2 * x+ + cGam3 * x- + cGam4 * x+ * x- = Gamma_new - cGam1;

Solve (m2, Gamma) equation system => r2 * x-^2 + r1 * x- + r0 = 0.

Define position of new trial vertex.

Step up to new region if new x- > 1.

Step down to new region if new x+ < 0.

Store breakup vertex information from the fragmentation process.

Else we have found the correct region, and can set the new colour index and return four-momentum.

End of "infinite" loop of stepping to new region.

Vec4 kinematicsHadronTmp	(	StringSystem	system,
		Vec4	pRem,
		double	phi,
		double	mult
	)

Generate momentum for some possible next hadron, based on mean values to get an estimate for rapidity and pT.

Now estimate the energy the next hadron will take.

Modify Gamma value in case of earlier fails.

Special case of first hadron.

Negative energy signals failure.

First make a copy of all variables to not overwrite anything.

Set up references that are direction-neutral; ...Dir for direction of iteration and ...Inv for its inverse.

Start search for new breakup in the old region.

Each step corresponds to trying a new string region.

Referance to current string region.

Now begin special section for rapid processing of low region.

A first step within a low region is easy. Make sure we use this region in case it's the last one.

Translate into x coordinates.

Find and return four-momentum of the produced particle.

A first step out of a low region also OK, if there are more regions. Negative energy signals failure, i.e. in last region.

Should be covered by the above check.

Momentum taken by stepping out of region. Continue to next region.

Else, for first step, take into account starting pT.

Now begin normal treatment of nontrivial regions. Set up four-vectors in a region not visited before.

If new region is vanishingly small, continue immediately to next. Negative energy signals failure to do this, i.e. moved too low.

Reexpress pTNew w.r.t. base vectors in new region, if possible. Recall minus sign from normalization e_x^2 = e_y^2 = -1.

Four-momentum taken so far, including new pT.

Derive coefficients for m2 expression. cM2 * x+ + cM3 * x- + cM4 * x+ * x- = m^2 - cM1;

Derive coefficients for Gamma expression. cGam2 * x+ + cGam3 * x- + cGam4 * x+ * x- = Gamma_new - cGam1;

Solve (m2, Gamma) equation system => r2 * x-^2 + r1 * x- + r0 = 0.

Define position of new trial vertex.

Step up to new region if new x- > 1.

Step down to new region if new x+ < 0.

Else we have found the correct region, and can return four-momentum.

End of "infinite" loop of stepping to new region.

void newHadron	(	double	kappaRatio,
		bool	forbidPopcornNow = false,
		bool	allowPop = true,
		double	strangeFac = 0.,
		double	probQQmod = 1.
	)

Fragment off one hadron from the string system, in flavour and pT.

Avoid contradiction in allowPop and forbidPopcornNow.

In case we are using the thermal model or Gaussian with mT2 suppression we have to pick the pT first.

Pick its transverse momentum.

Pick new flavour and form a new hadron. For forbidPopcornNow == true it must be a baryon.

Get its mass and thereby define its transverse mass.

In case of the Gaussian without mT2 suppression we pick the new flavour first to make the width flavour dependent.

Pick new flavour and form a new hadron. For forbidPopcornNow == true it must be a baryon.

Reinitialise probabilities if close-packing.

Pick its transverse momentum.

Pick its mass and thereby define its transverse mass.

void pearlHadron	(	StringSystem &	system,
		int	idPearlIn,
		Vec4	pPearlIn
	)

Creation of pearl hadron.

Make (anti)baryon from stepping over pearl (anti)quark.

Find transverse momentum contribution of pearl in current region.

Define baryon including pearl.

void setUp	(	bool	fromPosIn,
		int	iEndIn,
		int	idOldIn,
		int	iMaxIn,
		double	pxIn,
		double	pyIn,
		double	GammaIn,
		double	xPosIn,
		double	xNegIn,
		int	colIn
	)

Set up initial endpoint values from input.

Simple transcription from input.

Member Data Documentation

const double MEANMMIN = 0.2

static

Fictitious typical mass and pT used to look ahead for approximately where the next hadron will be produced, to quantify string close-packing there.

const double TINY = 1e-6

static

Constants: could only be changed in the code itself.

The StringEnd class.

Constants: could be changed here if desired, but normally should not. Avoid unphysical solutions to equation system.

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

• include/Pythia8/StringFragmentation.h
• src/StringFragmentation.cc