This is the class definition for the UA5Handler. More...

#include <UA5Handler.h>

Inheritance diagram for Herwig::UA5Handler:

Public Member Functions
virtual void	handle (EventHandler &eh, const tPVector &tagged, const Hint &hint)
	This is the routine that starts the algorithm.
Standard constructors and destructors.
	UA5Handler ()
	The default constructor.
Functions used by the persistent I/O system.
void	persistentOutput (PersistentOStream &os) const
	Function used to write out object persistently.
void	persistentInput (PersistentIStream &is, int version)
	Function used to read in object persistently.
Static Public Member Functions
static void	Init ()
	The standard Init function used to initialize the interfaces.
Protected Member Functions
Clone Methods.
virtual IBPtr	clone () const
	Make a simple clone of this object.
virtual IBPtr	fullclone () const
	Make a clone of this object, possibly modifying the cloned object to make it sane.
Private Member Functions
LorentzRotation	rotate (const LorentzMomentum &p) const
	This returns the rotation matrix needed to rotate p into the z axis.
UA5Handler &	operator= (const UA5Handler &)
	This is never defined and since it can never be called it isn't needed.

void	performDecay (PPtr parent, int &totalcharge, int &numbercharge) const
	Members to decay the clusters and hadrons produced in their decay, and insert the output in the event record.
void	decayCluster (ClusterPtr cluster, bool single) const
	Decay a cluster to two hadrons is sufficiently massive and to one if not.
void	insertParticle (PPtr particle, StepPtr step, bool all) const
	Recursively add particle and decay products to the step.

double	negativeBinomial (int N, double mean, double ek) const
	Members to generate the multiplicity according to a negative binomial distribution.
double	meanMultiplicity (Energy E) const
	The value of the mean multiplicity for a given energy E.
unsigned int	multiplicity (Energy E) const
	Generates a multiplicity for the energy E according to the negative binomial distribution.

void	generateMomentum (tClusterPtr clu1, tClusterPtr clu2, const ClusterVector &clusters, Energy CME, const Lorentz5Momentum &cm) const
	Members to generate the momenta of the clusters.
void	generateCylindricalPS (const ClusterVector &clusters, Energy CME) const
	The implementation of the cylindrical phase space.

template<typename T >
T	gaussDistribution (T mean, T stdev) const
	Various methods to generate random distributions.
double	randUng (double A, double B) const
	This returns a random number with a flat distribution [-A,A] plus gaussian tail with stdev B TODO: Should move this to Utilities.
template<typename T >
void	randAzm (T pt, T &px, T &py) const
	Generates a random azimuthal angle and puts x onto px and py TODO: Should move this to Utilities.
Energy	randExt (Energy AM0, InvEnergy B) const
	This returns random number from $dN/dp_T^2=exp(-p_{1,2,3}m_T$ distribution, where $m_T=\sqrt{p_T^2+M^2}$ .
Private Attributes
ClusterFissionerPtr	clusterFissioner
	Reference to the ClusterFissioner object.
ClusterDecayerPtr	clusterDecayer
	Reference to the cluster decayer object.
double	_probSoft
	This is the probability of having a soft underlying event.
double	_enhanceCM
	This is a parameter used to enhance the CM energy used to generate the multiplicity distribution.
unsigned int	_maxtries
	The maximum number of attempts to generate the distribution.
bool	_needWarning
	Whether to warn about using UA5 and MPI simultaneously.

double	_n1
	Parameters for the mean multiplicity $\bar n =n_1s^{n_2}+n_3$ .
double	_n2
	The parameter .
double	_n3
	The parameter .

double	_k1
	Parameters for in the negative binomial distribution given by $1/k =k_1\ln s+k_2$ .
double	_k2
	The parameter .

Energy	_m1
	Parameters for the cluster mass distribution, $M = m_{q1}+m_{q2}+m_1-\log(r_1 r_2)/m_2$ .
InvEnergy	_m2
	The parameter .

InvEnergy	_p1
	Parameters for the transverpse momentum of the soft distribution, $P(p_T) \propto p_T*exp(-p_i\sqrt{p_T^2+M^2}$ .
InvEnergy	_p2
	The parameter for strange and charm quarks.
InvEnergy	_p3
	The parameter for diquarks.
Static Private Attributes
static ClassDescription < UA5Handler >	initUA5Handler
	The static object used to initialize the description of this class.

Detailed Description

This is the class definition for the UA5Handler.

This class is designed to generate an underlying event based on the UA5 model. This is intended as a basic underlying event model which will be superceded by a new model in Herwig++.

This class interfaces with the cluster hadronization. To that end there is an interface set up with the ClusterFissioner class and with the ClusterDecayer class.

The Hadronization is responsible for the formation of the beam clusters. In this step the colour connection between the spectators and the initial-state parton showers is cut by the forced emission of a soft quark-antiquark pair. The underlying soft event in a hard hadron-hadron collision is then assumed to be a soft collision between these two beam clusters.

The model used for the underlying event is based on the minimum-bias $p\bar{p}$ event generator of the UA5 Collaboration, UA5 Collaboration, G.J. Alner et al., Nucl. Phys. B291 (1987) 445, modified to make use of our cluster fragmentation algorithm.

The parameter ProbSoft enables one to produce an underlying event in only a fraction ProbSoft of events (default=1.0).

The UA5 model starts from a parametrization of the $p\bar{p}$ inelastic charged multiplicity distribution as a negative binomial distribution,

$P(n) = \frac{\Gamma(n+k)}{n!\,\Gamma(k)} \frac{(\bar n/k)^n}{(1+\bar n/k)^{n+k}}\;.$

The parameter $k$ is given by

$1/k =k_1\ln s+k_2,$

and $\bar n$ is given by

$\bar n =n_1s^{n_2}+n_3$

As an option, for underlying events the value of $\sqrt{s}$ used to choose the multiplicity $n$ may be increased by a factor EnhanceCM to allow for an enhanced underlying activity in hard events.

Once a charged multiplicity has been selected from the above distribution, `softclusters' are generated with flavours $(f_1,f_2) = (q_{n-1},\bar q_n)$ by drawing $q_n\bar q_n = u\bar u$ or $d\bar d$ randomly from the vacuum. Soft cluster masses are assigned as

$M = m_{q1}+m_{q2}+m_1-\log(r_1 r_2)/m_2$

where $r_{1,2}$ are random numbers, which gives a (shifted) exponential distribution of $M^2$ . The parameters $m_1$ and $m_2$ control the distribution and $m_{q1,2}$ are the masses of the quarks in the cluster.

As each soft cluster is generated, it is decayed to stable hadrons using the cluster hadronization model (without cluster fission) and the accumulated charged multiplicity is computed. Once the preselected charged multiplicity is exactly reached, cluster generation is stopped. If it is exceeded, all clusters are rejected and new ones are generated until the exact value is reached. In this way the multiplicity distribution of stable charged hadrons is generated exactly as prescribed.

At this stage (to save time) the kinematic distribution of the soft clusters has not yet been generated. The decay products of each cluster are stored in its rest frame. Now the transverse momenta of the clusters are generated with the distribution

$P(p_t)\propto p_t\exp\left(-p_{1,2,3}\sqrt{p_t^2+M^2}\right)$

where the slope parameter $p_{1,2,3}$ depends as indicated on the flavour of the quark or diquark pair created in the primary cluster decay, $p_1$ for light quarks, $p_2$ for the strange and charm quarks and $p_3$ for diquarks. Next the clusters are given a flat rapidity distribution with Gaussian shoulders. The `reduced rapidities' $\xi_i$ are generated first by drawing from a distribution

$P(\xi) = N\;\;\;\mbox{for}\;|\xi|<0.6$

$P(\xi) = N\,e^{-(\xi-0.6)^2/2} \;\;\;\mbox{for}\;\xi>0.6$

$P(\xi) = N\,e^{-(\xi+0.6)^2/2} \;\;\;\mbox{for}\;\xi<-0.6$

where $N=1/(1.2+\sqrt{2\pi})$ is the normalization. Next a scaling factor $Y$ is computed such that the scaled cluster rapidities $y_i=Y\xi_i$ , their masses and transverse momenta satisfy momentum conservation when compared to the total energy of the underlying event. Thus the soft cluster rapidity distribution retains its overall shape but becomes higher and wider as the energy of the underlying event increases.

Finally the decay products of each cluster are boosted from its rest frame into the lab frame and added to the event record.

See also:: The interfaces defined for UA5Handler..

Definition at line 109 of file UA5Handler.h.

Member Function Documentation

virtual IBPtr Herwig::UA5Handler::clone ( ) const [protected, virtual]

Make a simple clone of this object.

Returns:: a pointer to the new object.

Implements ThePEG::InterfacedBase.

void Herwig::UA5Handler::decayCluster	(	ClusterPtr	cluster,
		bool	single
	)		const `[private]`

Decay a cluster to two hadrons is sufficiently massive and to one if not.

Parameters:

cluster	The cluster to decay
single	Whether or not ot allow decays to

virtual IBPtr Herwig::UA5Handler::fullclone ( ) const [protected, virtual]

Make a clone of this object, possibly modifying the cloned object to make it sane.

Returns:: a pointer to the new object.

Reimplemented from ThePEG::InterfacedBase.

template<typename T >

T Herwig::UA5Handler::gaussDistribution	(	T	mean,
		T	stdev
	)		const `[inline, private]`

Various methods to generate random distributions.

Gaussian distribution

Parameters:

mean	the mean of the distribution
stdev	the standard deviation of the distribution

Returns:: Arandom value from the gaussian distribution

void Herwig::UA5Handler::generateCylindricalPS	(	const ClusterVector &	clusters,
		Energy	CME
	)		const `[private]`

The implementation of the cylindrical phase space.

Parameters:

clusters	The list of clusters to generate the momentum for
CME	The center of mass energy

void Herwig::UA5Handler::generateMomentum	(	tClusterPtr	clu1,
		tClusterPtr	clu2,
		const ClusterVector &	clusters,
		Energy	CME,
		const Lorentz5Momentum &	cm
	)		const `[private]`

Members to generate the momenta of the clusters.

This generates the momentum of the produced particles according to the cylindrical phase space algorithm given in Computer Physics Communications 9 (1975) 297-304 by S. Jadach.

Parameters:

clu1	The first incoming cluster
clu2	The second incoming cluster
clusters	The list of clusters produced
CME	The center of mass energy
cm	The center of mass momentum (of the underlying event)

virtual void Herwig::UA5Handler::handle	(	EventHandler &	eh,
		const tPVector &	tagged,
		const Hint &	hint
	)		`[virtual]`

This is the routine that starts the algorithm.

Parameters:

eh	the EventHandler in charge of the generation.
tagged	the vector of particles to consider. If empty, all final state particles in the current Step is considered.
hint	a possible Hint which is ignored in this implementation

Implements ThePEG::StepHandler.

static void Herwig::UA5Handler::Init ( ) [static]

The standard Init function used to initialize the interfaces.

Called exactly once for each class by the class description system before the main function starts or when this class is dynamically loaded.

Reimplemented from ThePEG::HadronizationHandler.

void Herwig::UA5Handler::insertParticle	(	PPtr	particle,
		StepPtr	step,
		bool	all
	)		const `[private]`

Recursively add particle and decay products to the step.

Parameters:

particle	The particle
step	The step
all	Insert this particle as well as children

double Herwig::UA5Handler::meanMultiplicity ( Energy E ) const [inline, private]

The value of the mean multiplicity for a given energy E.

This is $n_1E^{2n_2}+n_3$ wher $n_1$ , $n_2$ and $n_3$ are parameters.

Parameters:

E	the energy to calculate the mean multiplicity for

Returns:: the mean multiplicity

unsigned int Herwig::UA5Handler::multiplicity ( Energy E ) const [private]

Generates a multiplicity for the energy E according to the negative binomial distribution.

Parameters:

E	The energy to generate for

Returns:: the randomly generated multiplicity for the energy given

double Herwig::UA5Handler::negativeBinomial	(	int	N,
		double	mean,
		double	ek
	)		const `[inline, private]`

Members to generate the multiplicity according to a negative binomial distribution.

Calculate the negative binomial probability given the mean $\bar n$ , the multiplicity and $1/k$ .

Parameters:

N	The multplicity for which to calculate the probability
mean	The mean multiplicity $\bar n$
ek

Returns:: a value distributed according the negative binomial distribution

UA5Handler& Herwig::UA5Handler::operator= ( const UA5Handler & ) [private]

This is never defined and since it can never be called it isn't needed.

The prototype is defined so the compiler doesn't use the default = operator.

void Herwig::UA5Handler::performDecay	(	PPtr	parent,
		int &	totalcharge,
		int &	numbercharge
	)		const `[private]`

Members to decay the clusters and hadrons produced in their decay, and insert the output in the event record.

Perform the decay of an unstable hadron.

Parameters:

parent	the decaying particle
totalcharge	The totalcharge of the decay proiducts
numbercharge	The number of stabel charged decay products

void Herwig::UA5Handler::persistentInput	(	PersistentIStream &	is,
		int	version
	)

Function used to read in object persistently.

Parameters:

is	the persistent input stream read from.
version	the version number of the object when written.

Reimplemented from ThePEG::Interfaced.

void Herwig::UA5Handler::persistentOutput ( PersistentOStream & os ) const

Function used to write out object persistently.

Parameters:

os	the persistent output stream written to.

Reimplemented from ThePEG::Interfaced.

template<typename T >

void Herwig::UA5Handler::randAzm	(	T	pt,
		T &	px,
		T &	py
	)		const `[inline, private]`

Generates a random azimuthal angle and puts x onto px and py TODO: Should move this to Utilities.

Parameters:

pt	The magnitude of the transverse momentum
px	The x component after random rotation
py	The y component after random rotation

Energy Herwig::UA5Handler::randExt	(	Energy	AM0,
		InvEnergy	B
	)		const `[inline, private]`

This returns random number from $dN/dp_T^2=exp(-p_{1,2,3}m_T$ distribution, where $m_T=\sqrt{p_T^2+M^2}$ .

It uses Newton's method to solve $F-R=0$

Parameters:

AM0	The mass .
B	The slope

Returns:: the value distributed from $dN/dp_T^2=exp(-p_{1,2,3}m_T$ with mean av

double Herwig::UA5Handler::randUng	(	double	A,
		double	B
	)		const `[inline, private]`

This returns a random number with a flat distribution [-A,A] plus gaussian tail with stdev B TODO: Should move this to Utilities.

Parameters:

A	The width of the flat part
B	The standard deviation of the gaussian tail

Returns:: the randomly generated value

Member Data Documentation

double Herwig::UA5Handler::_k1 [private]

Parameters for $k$ in the negative binomial distribution given by $1/k =k_1\ln s+k_2$ .

The parameter $k_1$

Definition at line 371 of file UA5Handler.h.

Energy Herwig::UA5Handler::_m1 [private]

Parameters for the cluster mass distribution, $M = m_{q1}+m_{q2}+m_1-\log(r_1 r_2)/m_2$ .

The parameter $m_1$

Definition at line 387 of file UA5Handler.h.

double Herwig::UA5Handler::_n1 [private]

Parameters for the mean multiplicity $\bar n =n_1s^{n_2}+n_3$ .

The parameter $n_1$

Definition at line 350 of file UA5Handler.h.

InvEnergy Herwig::UA5Handler::_p1 [private]

Parameters for the transverpse momentum of the soft distribution, $P(p_T) \propto p_T*exp(-p_i\sqrt{p_T^2+M^2}$ .

The parameter $p_1$ for light quarks

Definition at line 403 of file UA5Handler.h.

ClassDescription<UA5Handler> Herwig::UA5Handler::initUA5Handler [static, private]

The static object used to initialize the description of this class.

Indicates that this is a concrete class with persistent data.

Definition at line 322 of file UA5Handler.h.

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

UA5Handler.h

Public Member Functions

Static Public Member Functions

Protected Member Functions

Private Member Functions

Private Attributes

Static Private Attributes

Detailed Description

Member Function Documentation

Member Data Documentation