/usr/include/Pythia8/Pythia8/HelicityMatrixElements.h is in libpythia8-dev 8.1.80-1.
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// Copyright (C) 2013 Philip Ilten, Torbjorn Sjostrand.
// PYTHIA is licenced under the GNU GPL version 2, see COPYING for details.
// Please respect the MCnet Guidelines, see GUIDELINES for details.
// Header file for a number of physics classes used in tau decays.
#ifndef Pythia8_HelicityMatrixElements_H
#define Pythia8_HelicityMatrixElements_H
#include "Pythia8/Basics.h"
#include "Pythia8/Event.h"
#include "Pythia8/HelicityBasics.h"
#include "Pythia8/PythiaComplex.h"
#include "Pythia8/PythiaStdlib.h"
#include "Pythia8/StandardModel.h"
namespace Pythia8 {
//==========================================================================
// The helicity matrix element class.
class HelicityMatrixElement {
public:
// Constructor and destructor.
HelicityMatrixElement() {};
virtual ~HelicityMatrixElement() {};
// Initialize the physics matrices and pointers.
virtual void initPointers(ParticleData*, Couplings*);
// Initialize the channel.
virtual HelicityMatrixElement* initChannel(vector<HelicityParticle>&);
// Calculate the matrix element weight for a decay.
virtual double decayWeight(vector<HelicityParticle>&);
// Calculate the maximum matrix element decay weight.
virtual double decayWeightMax(vector<HelicityParticle>&)
{return DECAYWEIGHTMAX;}
// Calculate the helicity matrix element.
virtual complex calculateME(vector<int>){return complex(0,0);}
// Calculate the decay matrix for a particle.
virtual void calculateD(vector<HelicityParticle>&);
// Calculate the density matrix for a particle.
virtual void calculateRho(unsigned int, vector<HelicityParticle>&);
// Set a fermion line.
void setFermionLine(int, HelicityParticle&, HelicityParticle&);
// Calculate Breit-Wigner's with running widths and fixed.
virtual complex breitWigner(double s, double M, double G);
virtual complex sBreitWigner(double m0, double m1, double s,
double M, double G);
virtual complex pBreitWigner(double m0, double m1, double s,
double M, double G);
virtual complex dBreitWigner(double m0, double m1, double s,
double M, double G);
protected:
// Maximum decay weight. WARNING: hardcoded constant.
double DECAYWEIGHTMAX;
// Physics matrices.
vector< GammaMatrix > gamma;
// Particle map vector.
vector< int > pMap;
// Particle ID vector.
vector< int > pID;
// Particle mass vector.
vector< double > pM;
// Wave functions.
vector< vector< Wave4 > > u;
// Initialize the constants for the matrix element (called by initChannel).
virtual void initConstants() {};
// Initialize the wave functions (called by decayWeight and calculateRho/D).
virtual void initWaves(vector<HelicityParticle>&) {};
// Pointer to particle data.
ParticleData* particleDataPtr;
// Pointer to Standard Model constants.
Couplings* couplingsPtr;
private:
// Recursive sub-method to calculate the density matrix for a particle.
void calculateRho(unsigned int, vector<HelicityParticle>&,
vector<int>&, vector<int>&, unsigned int);
// Recursive sub-method to calculate the decay matrix for a particle.
void calculateD(vector<HelicityParticle>&, vector<int>&, vector<int>&,
unsigned int);
// Recursive sub-method to calculate the matrix element weight for a decay.
void decayWeight(vector<HelicityParticle>&, vector<int>&, vector<int>&,
complex&, unsigned int);
// Calculate the product of the decay matrices for a hard process.
complex calculateProductD(unsigned int, unsigned int,
vector<HelicityParticle>&, vector<int>&, vector<int>&);
// Calculate the product of the decay matrices for a decay process.
complex calculateProductD(vector<HelicityParticle>&,
vector<int>&, vector<int>&);
};
//==========================================================================
// Helicity matrix element for the hard process of two fermions -> W ->
// two fermions.
class HMETwoFermions2W2TwoFermions : public HelicityMatrixElement {
public:
void initWaves(vector<HelicityParticle>&);
complex calculateME(vector<int>);
};
//==========================================================================
// Helicity matrix element for the hard process of two fermions ->
// photon -> two fermions.
class HMETwoFermions2Gamma2TwoFermions : public HelicityMatrixElement {
public:
void initWaves(vector<HelicityParticle>&);
complex calculateME(vector<int>);
private:
// Fermion line charge and interaction energy.
double p0Q, p2Q, s;
};
//==========================================================================
// Helicity matrix element for the hard process of two fermions ->
// Z -> two fermions.
class HMETwoFermions2Z2TwoFermions : public HelicityMatrixElement {
public:
void initConstants();
void initWaves(vector<HelicityParticle>&);
complex calculateME(vector<int>);
private:
// Vector and axial couplings.
double p0CA, p2CA, p0CV, p2CV;
// Weinberg angle, Z width (on-shell), Z mass (on-shell), and s.
double cos2W, sin2W, zG, zM, s;
// Bool whether the incoming fermions are oriented with the z-axis.
bool zaxis;
};
//==========================================================================
// Helicity matrix element for the hard process of two fermions ->
// photon/Z -> two fermions with full interference.
// In general the initPointers and initChannel methods should not need to be
// redeclared, but in this case each matrix element needs to be initialized.
class HMETwoFermions2GammaZ2TwoFermions : public HelicityMatrixElement {
public:
HelicityMatrixElement* initChannel(vector<HelicityParticle>&);
void initPointers(ParticleData*, Couplings*);
void initWaves(vector<HelicityParticle>&);
complex calculateME(vector<int>);
private:
HMETwoFermions2Z2TwoFermions zHME;
HMETwoFermions2Gamma2TwoFermions gHME;
};
//==========================================================================
// Helicity matrix element for the hard process of Z -> two fermions.
class HMEZ2TwoFermions : public HelicityMatrixElement {
public:
void initConstants();
void initWaves(vector<HelicityParticle>&);
complex calculateME(vector<int>);
private:
// Vector and axial couplings.
double p2CA, p2CV;
};
//==========================================================================
// Helicity matrix element for the decay of a CP even Higgs -> two fermions.
// Because the Higgs is spin zero the Higgs production mechanism is not
// needed for calculating helicity density matrices.
class HMEHiggsEven2TwoFermions : public HelicityMatrixElement {
public:
void initWaves(vector<HelicityParticle>&);
complex calculateME(vector<int>);
private:
// Coupling constants of the fermions with the Higgs.
double p2CA, p2CV;
};
//==========================================================================
// Helicity matrix element for the decay of a CP odd Higgs -> two fermions.
class HMEHiggsOdd2TwoFermions : public HelicityMatrixElement {
public:
void initWaves(vector<HelicityParticle>&);
complex calculateME(vector<int>);
private:
// Coupling constants of the fermions with the Higgs.
double p2CA, p2CV;
};
//==========================================================================
// Helicity matrix element for the decay of a charged Higgs -> two fermions.
class HMEHiggsCharged2TwoFermions : public HelicityMatrixElement {
public:
void initWaves(vector<HelicityParticle>&);
complex calculateME(vector<int>);
private:
// Coupling constants of the fermions with the Higgs.
double p2CA, p2CV;
};
//==========================================================================
// Helicity matrix element which provides an unpolarized on-diagonal helicity
// density matrix. Used for unknown hard processes.
class HMEUnpolarized : public HelicityMatrixElement {
public:
void calculateRho(unsigned int, vector<HelicityParticle>&);
};
//==========================================================================
// Base class for all tau decay helicity matrix elements.
class HMETauDecay : public HelicityMatrixElement {
public:
virtual void initWaves(vector<HelicityParticle>&);
virtual complex calculateME(vector<int>);
virtual double decayWeightMax(vector<HelicityParticle>&);
protected:
virtual void initHadronicCurrent(vector<HelicityParticle>&) {};
virtual void calculateResonanceWeights(vector<double>&, vector<double>&,
vector<complex>&);
};
//==========================================================================
// Helicity matrix element for a tau decaying into a single scalar meson.
class HMETau2Meson : public HMETauDecay {
public:
void initConstants();
void initHadronicCurrent(vector<HelicityParticle>&);
};
//==========================================================================
// Helicity matrix element for a tau decaying into two leptons.
class HMETau2TwoLeptons : public HMETauDecay {
public:
void initConstants();
void initWaves(vector<HelicityParticle>&);
complex calculateME(vector<int>);
};
//==========================================================================
// Helicity matrix element for a tau decaying into two mesons through a
// vector meson resonance.
class HMETau2TwoMesonsViaVector : public HMETauDecay {
public:
void initConstants();
void initHadronicCurrent(vector<HelicityParticle>&);
private:
// Resonance masses, widths, and weights.
vector<double> vecM, vecG, vecP, vecA;
vector<complex> vecW;
};
//==========================================================================
// Helicity matrix element for a tau decay into two mesons through a vector
// or scalar meson resonance.
class HMETau2TwoMesonsViaVectorScalar : public HMETauDecay {
public:
void initConstants();
void initHadronicCurrent(vector<HelicityParticle>&);
private:
// Coupling to vector and scalar resonances.
double scaC, vecC;
// Resonance masses, widths, and weights.
vector<double> scaM, scaG, scaP, scaA, vecM, vecG, vecP, vecA;
vector<complex> scaW, vecW;
};
//==========================================================================
// Helicity matrix element for a tau decay into three mesons (base class).
class HMETau2ThreeMesons : public HMETauDecay {
public:
void initConstants();
void initHadronicCurrent(vector<HelicityParticle>&);
protected:
// Decay mode of the tau.
enum Mode{Pi0Pi0Pim, PimPimPip, Pi0PimK0b, PimPipKm, Pi0PimEta, PimKmKp,
Pi0K0Km, KlPimKs, Pi0Pi0Km, KlKlPim, PimKsKs, PimK0bK0, Uknown};
Mode mode;
// Initialize decay mode and resonance constants (called by initConstants).
virtual void initMode();
virtual void initResonances() {;}
// Initialize the momenta.
virtual void initMomenta(vector<HelicityParticle>&);
// Center of mass energies and momenta.
double s1, s2, s3, s4;
Wave4 q, q2, q3, q4;
// Stored a1 Breit-Wigner (for speed).
complex a1BW;
// Form factors.
virtual complex F1() {return complex(0, 0);}
virtual complex F2() {return complex(0, 0);}
virtual complex F3() {return complex(0, 0);}
virtual complex F4() {return complex(0, 0);}
// Phase space and Breit-Wigner for the a1.
virtual double a1PhaseSpace(double);
virtual complex a1BreitWigner(double);
// Sum running p and fixed width Breit-Wigner resonances.
complex T(double m0, double m1, double s,
vector<double>& M, vector<double>& G, vector<double>& W);
complex T(double s, vector<double>& M, vector<double>& G, vector<double>& W);
};
//==========================================================================
// Helicity matrix element for a tau decay into three pions.
class HMETau2ThreePions : public HMETau2ThreeMesons {
private:
void initResonances();
// Resonance masses, widths, and weights.
vector<double> rhoM, rhoG, rhoPp, rhoAp, rhoPd, rhoAd;
double f0M, f0G, f0P, f0A, f2M, f2G, f2P, f2A;
double sigM, sigG, sigP, sigA;
vector<complex> rhoWp, rhoWd;
complex f0W, f2W, sigW;
// Form factors.
complex F1();
complex F2();
complex F3();
// Running width and Breit-Wigner for the a1.
double a1PhaseSpace(double);
complex a1BreitWigner(double);
};
//==========================================================================
// Helicity matrix element for a tau decay into three mesons with kaons.
class HMETau2ThreeMesonsWithKaons : public HMETau2ThreeMesons {
private:
void initResonances();
// Resonance masses, widths, and weights.
vector<double> rhoMa, rhoGa, rhoWa, rhoMv, rhoGv, rhoWv;
vector<double> kstarMa, kstarGa, kstarWa, kstarMv, kstarGv, kstarWv;
vector<double> k1Ma, k1Ga, k1Wa, k1Mb, k1Gb, k1Wb;
vector<double> omegaM, omegaG, omegaW;
double kM, piM, piW;
// Form factors.
complex F1();
complex F2();
complex F4();
};
//==========================================================================
// Helicity matrix element for a tau decay into generic three mesons.
class HMETau2ThreeMesonsGeneric : public HMETau2ThreeMesons {
private:
void initResonances();
// Resonance masses, widths, and weights.
vector<double> rhoMa, rhoGa, rhoWa, rhoMv, rhoGv, rhoWv;
vector<double> kstarM, kstarG, kstarW, k1M, k1G, k1W;
double kM, piM, piW;
// Form factors.
complex F1();
complex F2();
complex F4();
};
//==========================================================================
// Helicity matrix element for a tau decay into two pions and a photon.
class HMETau2TwoPionsGamma : public HMETauDecay {
public:
void initConstants();
void initWaves(vector<HelicityParticle>&);
complex calculateME(vector<int>);
protected:
// Resonance masses, widths, and weights.
vector<double> rhoM, rhoG, rhoW, omegaM, omegaG, omegaW;
double piM;
// Form factor.
complex F(double s, vector<double> M, vector<double> G, vector<double> W);
};
//==========================================================================
// Helicity matrix element for a tau decay into four pions.
class HMETau2FourPions : public HMETauDecay {
public:
void initConstants();
void initHadronicCurrent(vector<HelicityParticle>& p);
private:
// G-function form factors (fits).
double G(int i, double s);
// T-vector functions.
Wave4 t1(Wave4&, Wave4&, Wave4&, Wave4&, Wave4&);
Wave4 t2(Wave4&, Wave4&, Wave4&, Wave4&, Wave4&);
Wave4 t3(Wave4&, Wave4&, Wave4&, Wave4&, Wave4&);
// Breit-Wigner denominators for the intermediate mesons.
complex a1D(double s);
complex rhoD(double s);
complex sigD(double s);
complex omeD(double s);
// Form factors needed for the a1, rho, and omega.
double a1FormFactor(double s);
double rhoFormFactor1(double s);
double rhoFormFactor2(double s);
double omeFormFactor(double s);
// Masses and widths of the intermediate mesons.
double a1M, a1G, rhoM, rhoG, sigM, sigG, omeM, omeG;
// Masses for the pions (charged and neutral).
double picM, pinM;
// Amplitude, phases, and weights for mixing.
double sigA, sigP, omeA, omeP;
complex sigW, omeW;
// Cut-off for a1 form factor.
double lambda2;
};
//==========================================================================
// Helicity matrix element for a tau decaying into five pions.
class HMETau2FivePions : public HMETauDecay {
public:
void initConstants();
void initHadronicCurrent(vector<HelicityParticle>&);
private:
// Hadronic currents.
Wave4 Ja(Wave4 &q, Wave4 &q1, Wave4 &q2, Wave4 &q3, Wave4 &q4, Wave4 &q5);
Wave4 Jb(Wave4 &q, Wave4 &q1, Wave4 &q2, Wave4 &q3, Wave4 &q4, Wave4 &q5);
// Simplified s-wave Breit-Wigner assuming massless products.
complex breitWigner(double s, double M, double G);
// Masses and widths of intermediates.
double a1M, a1G, rhoM, rhoG, omegaM, omegaG, omegaW, sigmaM, sigmaG, sigmaW;
};
//==========================================================================
// Helicity matrix element for a tau decay into flat phase space.
class HMETau2PhaseSpace : public HMETauDecay {
public:
void initWaves(vector<HelicityParticle>&) {};
complex calculateME(vector<int>) {return 1;}
void calculateD(vector<HelicityParticle>&) {};
void calculateRho(unsigned int, vector<HelicityParticle>&) {};
double decayWeight(vector<HelicityParticle>&) {return 1.0;}
double decayWeightMax(vector<HelicityParticle>&) {return 1.0;}
};
//==========================================================================
} // end namespace Pythia8
#endif // end Pythia8_HelicityMatrixElements_H
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