PEtaDoubleDalitz.cc

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//Eta double Dalitz decay
//
//References: ???
//
//                             Author:  I. Froehlich
//                             Written: 17.9.2009
//
 
#include "PEtaDoubleDalitz.h"
 
 
PDistribution* PEtaDoubleDalitz::Clone(const char*) const {
    //clone the object
    return new PEtaDoubleDalitz((const PEtaDoubleDalitz &)* this);
};
 
PEtaDoubleDalitz::PEtaDoubleDalitz(const Char_t *id, const Char_t *de, Int_t key) : PChannelModel(id, de, key) {
    //Constructor
    gRand = new TRandom2();
    dil1 = dil2 = parent = NULL;
};
 
Double_t PEtaDoubleDalitz::Gen2lepton1(Double_t m) {
    Double_t MEl  = PData::LMass("e+");
    Double_t MEl2 = 2*MEl;
    Double_t m2   = m*m;
    Double_t ARAND[2];
    Double_t WTD;
    Double_t AM;
    do {
        gRand->RndmArray(2, ARAND);
        AM = MEl2*TMath::Exp(TMath::Log(m/MEl2)*ARAND[0]);
        Double_t AM2 = AM*AM;
        Double_t RE  = MEl2*MEl2/AM2;
        WTD = TMath::Sqrt(1-RE)*(1+RE/2)*TMath::Power(1-AM2/m2,3);
    } while(ARAND[1]>WTD); // ???????????? while(ARAND[1]>WTD)
    return AM;
}
 
 
Bool_t PEtaDoubleDalitz::Init(void) {
 
    parent = GetParticle("parent");
    if (!parent) {
    Warning("Init", "Parent not found");
    return kFALSE;
    }
 
    dil1 = GetParticle("dilepton");
    dil2 = GetParticle("dilepton");
 
    if (!dil1 || !dil2) {
    Warning("Init", "Dileptons not found");
    return kFALSE;
    }
 
    formfactor_model =
    GetSecondaryModel("formfactor");
    if (formfactor_model)
    ff_w_max = formfactor_model->GetWeightMax();
    if (ff_w_max < 0) {
    Warning("Init", "Max value of the FF model not initialized, FF disabled");
    formfactor_model = NULL;
    }
    if (!formfactor_model) ff_w_max = 1.;
 
    return kTRUE;
}
 
Bool_t PEtaDoubleDalitz::SampleMass(void) {
 
    Double_t MEta = parent->M();
 
    Double_t weight = 1.;
    Double_t mVV[2];
    do {
    mVV[0] = Gen2lepton1(MEta);//IM of the 1-st pair e+e-
    mVV[1] = Gen2lepton1(MEta);//IM of the 2-nd pair e+e-
 
    if (formfactor_model && formfactor_model->GetVersionFlag(VERSION_SAMPLING)) {
        weight *= formfactor_model->GetWeight(mVV[0]);
        weight *= formfactor_model->GetWeight(mVV[1]);
    }
 
    } while((mVV[0]+mVV[1]>MEta) || ((weight/ff_w_max) < PUtils::sampleFlat())  );
 
 
    dil1->SetM(mVV[0]);
    dil2->SetM(mVV[1]);
 
    return kTRUE;
};
 
ClassImp(PEtaDoubleDalitz)