PEtaPiPiDileptonMass.cc

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//
// Decay eta -> pi+ pi- dilepton
// Model to sample the dilepton mass
//
// References:
// [L1] Thimo Petri and Andreas Wirzba
//      Internal Report, Juelich
//
//                                  Author:  I. Froehlich
 
 
using namespace std;
#include <sstream>
#include <iostream>
#include <iomanip>
 
#include "PEtaPiPiDileptonMass.h"
 
 
ClassImp(PEtaPiPiDileptonMass)
 
PEtaPiPiDileptonMass::PEtaPiPiDileptonMass() {
};
 
PEtaPiPiDileptonMass::PEtaPiPiDileptonMass(const Char_t *id, const Char_t *de, Int_t key) :
    PChannelModel(id, de, key) {
 
    if (is_channel < 0)
    Warning("PEtaPiPiDileptonMass", "This model should be bound to CHANNELS only");
 
    m_pi    = makeStaticData()->GetParticleMass("pi+");
    mass_e  = makeStaticData()->GetParticleMass("e-");
    mass_ee = 2.*mass_e;
    vmd_formfactor_model = NULL;
 
    //it is important to avoid energy conservation violation, otherwise
    //genbod will be much slower:
    SetDynamicRange(mass_ee,makeStaticData()->GetParticleMass("eta")-2*m_pi);
} ;
 
PDistribution* PEtaPiPiDileptonMass::Clone(const char*) const {
    return new PEtaPiPiDileptonMass((const PEtaPiPiDileptonMass &)* this);
};
 
Bool_t PEtaPiPiDileptonMass::Init(void) {
    //Init function called once for each PChannel
 
    //looking for parent. This is mandatory
    parent = GetParticle("parent");
    if (!parent) {
    Warning("Init", "Parent not found");
    return kFALSE;
    }
    pip = GetParticle("pi+");
    if (!pip) {
    Warning("Init", "Pi+ not found");
    return kFALSE;
    }
    pim = GetParticle("pi-");
    if (!pim) {
    Warning("Init", "Pi- not found");
    return kFALSE;
    }
    ep = GetParticle("e+");
    if (!ep) {
    Warning("Init", "e+ not found");
    return kFALSE;
    }
    em = GetParticle("e-");
    if (!em) {
    Warning("Init", "e- not found");
    return kFALSE;
    }
 
    vmd_formfactor_model =
    GetSecondaryModel("formfactor");
 
    return kTRUE;
}
 
 
Double_t PEtaPiPiDileptonMass::GetWeight(Double_t *mass, Int_t *) {
 
    //This is the mass-dependent part of eqn. 64 of Wirzba's report
 
    return GetMassWeight(mass[0]);
}
 
Double_t PEtaPiPiDileptonMass::GetMassWeight(Double_t mass) const {
 
    //Mass-dependent part of the eqn. 64
 
    if (mass < mass_ee) return 0.;
 
    Double_t weight = 1./(8*mass*mass);
 
    if (vmd_formfactor_model) {
    weight *= vmd_formfactor_model->GetWeight(mass);
    }
 
    return weight;
 
}
 
Bool_t PEtaPiPiDileptonMass::SampleMass(Double_t *mass, Int_t *) {
 
    mass[0] = this->GetRandom();
    return kTRUE;
}
 
Double_t PEtaPiPiDileptonMass::Eval(Double_t x, Double_t, Double_t, Double_t) const {
    //return mass of the dilepton for GetRandom sampling
 
    return GetMassWeight(x);
}
 
// Double_t PEtaPiPiDileptonMass::GetWeight(void) {
 
//     return GetWeight(dilepton->M());
// }