This class defines a sequential 2-body decay tree and generates events using the ROOT class TGenPhaseSpace. More...

#include <TwoBodyDecayGen.hxx>

Collaboration diagram for TwoBodyDecayGen:

Public Types
typedef std::pair< std::vector < TwoBodyDecayGen * >, double >	DauNode
	Node with B.F.
typedef std::vector< DauNode >	DauNodeVec
	Vector of nodes (channels)
typedef std::pair< unsigned, double >	chBFpair
	Channel id and B.F.

Public Member Functions
	TwoBodyDecayGen (double mommass, double dau1mass, double dau2mass, TwoBodyDecayGen dau1=NULL, TwoBodyDecayGen dau2=NULL)
	Constructor 1.
	TwoBodyDecayGen (double mommass, double daumasses, TwoBodyDecayGen dau1=NULL, TwoBodyDecayGen *dau2=NULL)
	Constructor 2.
	TwoBodyDecayGen (double *masses, unsigned nparts)
	Constructor that takes an array with particle masses for the entire decay tree.
bool	add_decay_channel (double *masses, unsigned nparts, double brfr)
	Add a new decay channel.
TwoBodyDecayGen *	get_daughter (unsigned chid, unsigned dauid)
	Return requested daughter decay node.
double	get_brfr (unsigned chid)
	Return BF for decay channel.
int	find_leaf_nodes (std::vector< std::deque< chBFpair > > &brfrVec, std::deque< chBFpair > &brfrQ)
	Find leaf branches or decay nodes.
double	generate (TLorentzVector &momp, std::vector< TLorentzVector > &particle_lvs, std::deque< chBFpair > chQ)
	Generate one event at a time.
TTree *	get_event_tree (unsigned nevents, TH1 *hmomp)
	Generate arbitrary number of events.
void	print (unsigned indent=0)
	Print decay tree.

Private Member Functions
void	_printQ (std::string prefix, std::deque< chBFpair > queue)
	Print queue for debugging.
void	_printQ (std::string prefix, std::vector< std::deque< chBFpair > > queue)
	Print vector of queues for debugging.

Private Attributes
TGenPhaseSpace	_generator
	Generator for the current decay vertex.
double	_mommass
	Mother particle mass for the current decay vertex.
double	_daumasses [NDAUS]
	Array of the two daughter masses.
DauNodeVec	_dauchannels
	Decay channels with BF (stored as pointers)

Static Private Attributes
static unsigned long long	_count
	Debug message counter.

Detailed Description

This class defines a sequential 2-body decay tree and generates events using the ROOT class TGenPhaseSpace.

Note that this is a very simple phase space event generator and is not aware of any resonances. The decay tree is stored as an array with particle masses and pointers to TwoBodyDecayGen instances for subsequent decay vertices. These pointers are NULL for leaf nodes in the decay tree. There are several constructors to instantiate a TwoBodyDecayGen object; use of the constructor which takes an array with particle masses and length of the decay tree (also the length of the particle mass array) is recommended for simplicity of use. Look at the constructor documentation for more details on the format.

Author:: Suvayu Ali Suvay.nosp@m.u.Al.nosp@m.i@cer.nosp@m.nNOS.nosp@m.PAM.c.nosp@m.h

Date:: 2012-11-05 Mon

Member Typedef Documentation

typedef std::pair<unsigned, double> TwoBodyDecayGen::chBFpair

Channel id and B.F.

pair

typedef std::pair<std::vector<TwoBodyDecayGen*>, double> TwoBodyDecayGen::DauNode

Node with B.F.

Constructor & Destructor Documentation

TwoBodyDecayGen::TwoBodyDecayGen	(	double	mommass,
		double	dau1mass,
		double	dau2mass,
		TwoBodyDecayGen *	dau1 = `NULL`,
		TwoBodyDecayGen *	dau2 = `NULL`
	)

Constructor 1.

Parameters:

mommass	Mass of the mother in GeV/c²
dau1mass	Mass of the first daughter in GeV/c²
dau2mass	Mass of the second daughter in GeV/c²
dau1	Pointer to TwoBodyDecayGen object for first daughter
dau2	Pointer to TwoBodyDecayGen object for second daughter

TwoBodyDecayGen::TwoBodyDecayGen	(	double	mommass,
		double *	daumasses,
		TwoBodyDecayGen *	dau1 = `NULL`,
		TwoBodyDecayGen *	dau2 = `NULL`
	)

Constructor 2.

Parameters:

mommass	Mass of the mother in GeV/c²
daumasses	Array of doubles with mass of the two daughters in GeV/c²
dau1	Pointer to TwoBodyDecayGen object for first daughter
dau2	Pointer to TwoBodyDecayGen object for second daughter

TwoBodyDecayGen::TwoBodyDecayGen	(	double *	masses,
		unsigned	nparts
	)

Constructor that takes an array with particle masses for the entire decay tree.

No need to create the different decay vertices in the right order any more. Instead, pass an array with all the particle masses and the number of particles (length of the array). The array should look something like these:

Bs → Ds*(Dsγ)ρ(ππ) double masses[7] = {Bs, Ds*, ρ, Ds, γ, π, π};
Bs → Ds*(Dsγ)π double masses[5] = {Bs, Ds*, π, Ds, γ};
Bs → Ds*(Dsπ)π double masses[5] = {Bs, Ds*, π, Ds, π};

NB: Only one level of decay vertices have been tested at the moment.

Parameters:

masses	Array of doubles with mass of all the particles in GeV/c²
nparts	Number of particles in the decay tree (length of the array)

Member Function Documentation

void TwoBodyDecayGen::_printQ	(	std::string	prefix,
		std::deque< chBFpair >	queue
	)

private

Print queue for debugging.

Parameters:

prefix	String prefix in output
queue	Queue to print

void TwoBodyDecayGen::_printQ	(	std::string	prefix,
		std::vector< std::deque< chBFpair > >	queue
	)

private

Print vector of queues for debugging.

Parameters:

prefix	String prefix in output
queue	Vector of queues to print

bool TwoBodyDecayGen::add_decay_channel	(	double *	masses,
		unsigned	nparts,
		double	brfr
	)

Add a new decay channel.

Parameters:

masses	Array of doubles with mass of all the particles in GeV/c²
nparts	Number of particles in the decay tree (length of the array)
brfr	Branching fraction for the channel

Returns:: Status

int TwoBodyDecayGen::find_leaf_nodes	(	std::vector< std::deque< chBFpair > > &	brfrVec,
		std::deque< chBFpair > &	brfrQ
	)

Find leaf branches or decay nodes.

This method traverses the decay tree and extracts the branching fraction and the channel id from each node into a double-ended queue. It stops the queue everytime a leaf node is encountered. The queue is then saved into a vector.

Implementation: Follow each daughter node, until a leaf node is found. Return the depth of the recursive call, so in the current function scope 0, increment it by 1 as we go up the tree. Once a leaf node is found, branch off the search to the other daughters one level above (recursion level = 1).

  (recursion depth)

  L3  - - -                     mother
                               /      \
                              /        \
  L2  - - -                  d1        d2 (leaf node)
                            /  \      /  \
                           /    \    /    \
  L1  - - -   (leaf node) d1    d2  d3    d4
                         /  \
                        /    \
  L0  - - -            d1    d2

NB: end points (d{2..4} @ L1 or d{1,2} @ L0) are stored as NULL pointers

Parameters:

brfrVec	Vector with deque for each leaf branch / decay node
brfrQ	Pointer to deque for each leaf branch / decay node

Returns:: Depth where leaf node was found (-ve numbers are invalid)

double TwoBodyDecayGen::generate	(	TLorentzVector &	momp,
		std::vector< TLorentzVector > &	particle_lvs,
		std::deque< chBFpair >	chQ
	)

Generate one event at a time.

Parameters:

momp	Mother 4-momentum
particle_lvs	std::vector used to return generated 4-momenta
chQ	Queue with channels to generate

Returns:: Event weight

double TwoBodyDecayGen::get_brfr ( unsigned chid )

Return BF for decay channel.

Parameters:

chid	Decay channel id

Returns:: Branching fraction for decay channel

TwoBodyDecayGen * TwoBodyDecayGen::get_daughter	(	unsigned	chid,
		unsigned	dauid
	)

Return requested daughter decay node.

Parameters:

chid	Decay channel id
dauid	Daughter number (0 or 1)

Returns:: Pointer to the daughter decay node

TTree * TwoBodyDecayGen::get_event_tree	(	unsigned	nevents,
		TH1 *	hmomp
	)

Generate arbitrary number of events.

Parameters:

nevents	Number of events to generate
hmomp	Histogram template for 3-momentum of the mother mother particle

Returns:: Generated event tree

void TwoBodyDecayGen::print ( unsigned indent = 0 )

Print decay tree.

Parameters:

indent Spaces to indent (to denote decay level)

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

Public Types

Public Member Functions

Private Member Functions

Private Attributes

Static Private Attributes

Detailed Description

Member Typedef Documentation

Constructor & Destructor Documentation

Member Function Documentation