DalitzMCMC Class Reference

#include <DalitzMCMC.h>

Public Member Functions
	DalitzMCMC (const DalitzEventPattern &pat, const unsigned int &seed=0)
void	FillEventList (DalitzEventList &evtList, const unsigned int &NEvents)
DalitzEvent	GetFlatEvent ()

Private Attributes
const DalitzEventPattern	_pat
const unsigned int	_nbody
MINT::MinuitParameterSet	_myOwnPSet
FitAmpSum	_pdf
TLorentzVector	_P
TGenPhaseSpace	_event

Detailed Description

Definition at line 12 of file DalitzMCMC.h.

Constructor & Destructor Documentation

DalitzMCMC()

DalitzMCMC::DalitzMCMC	(	const DalitzEventPattern &	pat,
		const unsigned int &	seed = 0
	)

Definition at line 8 of file DalitzMCMC.cpp.

  : _pat(pat)
  , _nbody(_pat.numDaughters())
  , _myOwnPSet()
  , _pdf(_pat, &_myOwnPSet)
{
  //Setup TGenPhaseSpace
  _P.SetXYZM( 0.0, 0.0, 0.0, _pat[0].mass() );

  std::vector<double> masses(_nbody);
  for( unsigned int i=0; i<_nbody; i++ )
    masses[i] = _pat[i+1].mass();

  gRandom->SetSeed(seed);
  _event.SetDecay(_P, _nbody, &masses[0]);
}

Member Function Documentation

FillEventList()

void DalitzMCMC::FillEventList	(	DalitzEventList &	evtList,
		const unsigned int &	NEvents
	)

Uses the Metropolis-Hastings algorithm (Markov Chain) to sample a Dalitz plot ampitude-squared probability density and fill a DalitzEventList.

Definition at line 26 of file DalitzMCMC.cpp.

{
  //Markov Chain
  double ratio;

  //Start event
  DalitzEvent candEvent_start = GetFlatEvent();

  //Next event
  DalitzEvent candEvent_next;

  for( unsigned int i=0; i<NEvents; i++ ){
    candEvent_next = GetFlatEvent();

    const double pdf_start = _pdf.Prob(candEvent_start);

    const double pdf_next = _pdf.Prob(candEvent_next);

    ratio = pdf_next/pdf_start;
    if( ratio >= 1.0 ){
      candEvent_start = candEvent_next;
      evtList.Add(candEvent_next);
    }else{
      const double height = gRandom->Rndm();
      if( height < ratio ){
    candEvent_start = candEvent_next;
    evtList.Add(candEvent_next);
      }else{
    evtList.Add(candEvent_start);
      }
    }
  }
}

GetFlatEvent()

DalitzEvent DalitzMCMC::GetFlatEvent

(

)

Performs hit-and-miss using TGenPhaseSpace to generate a uniformly distributed phase space event.

Definition at line 61 of file DalitzMCMC.cpp.

{
  std::vector<TLorentzVector> p4_mumAndDgtr(_nbody+1);

  //Fill mother momentum
  p4_mumAndDgtr[0] = _P;

  //Fill daughter momenta
  while(true){
    const double weight = _event.Generate();
    const double height = gRandom->Uniform(1.0/weight);

    if( height < 1.0 ){
      for( unsigned int i=0; i<_nbody; i++ )
    p4_mumAndDgtr[i+1] = *(_event.GetDecay(i));

      break;
    }
  }

  const DalitzEvent flatEvent(_pat, p4_mumAndDgtr);
  return flatEvent;
}

Member Data Documentation

_event

TGenPhaseSpace DalitzMCMC::_event

private

Definition at line 39 of file DalitzMCMC.h.

_myOwnPSet

MINT::MinuitParameterSet DalitzMCMC::_myOwnPSet

private

Definition at line 35 of file DalitzMCMC.h.

_nbody

const unsigned int DalitzMCMC::_nbody

private

Definition at line 33 of file DalitzMCMC.h.

_P

TLorentzVector DalitzMCMC::_P

private

Definition at line 38 of file DalitzMCMC.h.

_pat

const DalitzEventPattern DalitzMCMC::_pat

private

Definition at line 32 of file DalitzMCMC.h.

_pdf

FitAmpSum DalitzMCMC::_pdf

private

Definition at line 36 of file DalitzMCMC.h.

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

• Mint/DalitzMCMC.h
• src/Mojito/DalitzEventGeneration/DalitzMCMC.cpp