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diff --git a/EvtGenModels/EvtEta2MuMuGamma.hh b/EvtGenModels/EvtEta2MuMuGamma.hh
deleted file mode 100644
--- a/EvtGenModels/EvtEta2MuMuGamma.hh
+++ /dev/null
@@ -1,39 +0,0 @@
-
-/***********************************************************************
-* Copyright 1998-2020 CERN for the benefit of the EvtGen authors *
-* *
-* This file is part of EvtGen. *
-* *
-* EvtGen is free software: you can redistribute it and/or modify *
-* it under the terms of the GNU General Public License as published by *
-* the Free Software Foundation, either version 3 of the License, or *
-* (at your option) any later version. *
-* *
-* EvtGen is distributed in the hope that it will be useful, *
-* but WITHOUT ANY WARRANTY; without even the implied warranty of *
-* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the *
-* GNU General Public License for more details. *
-* *
-* You should have received a copy of the GNU General Public License *
-* along with EvtGen. If not, see <https://www.gnu.org/licenses/>. *
-***********************************************************************/
-
-#ifndef EVTETA2MUMUGAMMA_HH
-#define EVTETA2MUMUGAMMA_HH
-
-#include "EvtGenBase/EvtDecayProb.hh"
-
-class EvtParticle;
-
-class EvtEta2MuMuGamma : public EvtDecayProb {
- public:
- std::string getName() override;
- EvtDecayBase* clone() override;
-
- void init() override;
- void initProbMax() override;
-
- void decay( EvtParticle* p ) override;
-};
-
-#endif
diff --git a/EvtGenModels/EvtPi0Dalitz.hh b/EvtGenModels/EvtPi0Dalitz.hh
--- a/EvtGenModels/EvtPi0Dalitz.hh
+++ b/EvtGenModels/EvtPi0Dalitz.hh
@@ -34,6 +34,14 @@
void initProbMax() override;
void decay( EvtParticle* p ) override;
+
+ private:
+ double m_poleSize{ 0.00000002 };
+
+ // Following are rho mass and width, but in order to keep consistency
+ // with what was done before do not use data from particle table.
+ const double m_m0Sq{ 0.768 * 0.768 };
+ const double m_m0SqG0Sq{ m_m0Sq * 0.151 * 0.151 };
};
#endif
diff --git a/src/EvtGenModels/EvtEta2MuMuGamma.cpp b/src/EvtGenModels/EvtEta2MuMuGamma.cpp
deleted file mode 100644
--- a/src/EvtGenModels/EvtEta2MuMuGamma.cpp
+++ /dev/null
@@ -1,107 +0,0 @@
-
-/***********************************************************************
-* Copyright 1998-2020 CERN for the benefit of the EvtGen authors *
-* *
-* This file is part of EvtGen. *
-* *
-* EvtGen is free software: you can redistribute it and/or modify *
-* it under the terms of the GNU General Public License as published by *
-* the Free Software Foundation, either version 3 of the License, or *
-* (at your option) any later version. *
-* *
-* EvtGen is distributed in the hope that it will be useful, *
-* but WITHOUT ANY WARRANTY; without even the implied warranty of *
-* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the *
-* GNU General Public License for more details. *
-* *
-* You should have received a copy of the GNU General Public License *
-* along with EvtGen. If not, see <https://www.gnu.org/licenses/>. *
-***********************************************************************/
-
-#include "EvtGenModels/EvtEta2MuMuGamma.hh"
-
-#include "EvtGenBase/EvtDiracSpinor.hh"
-#include "EvtGenBase/EvtGenKine.hh"
-#include "EvtGenBase/EvtPDL.hh"
-#include "EvtGenBase/EvtParticle.hh"
-#include "EvtGenBase/EvtPatches.hh"
-#include "EvtGenBase/EvtReport.hh"
-#include "EvtGenBase/EvtTensor4C.hh"
-#include "EvtGenBase/EvtVector4C.hh"
-
-#include <fstream>
-#include <stdio.h>
-#include <stdlib.h>
-#include <string>
-using std::fstream;
-
-std::string EvtEta2MuMuGamma::getName()
-{
- return "ETA2MUMUGAMMA";
-}
-
-EvtDecayBase* EvtEta2MuMuGamma::clone()
-{
- return new EvtEta2MuMuGamma;
-}
-
-void EvtEta2MuMuGamma::initProbMax()
-{
- setProbMax( 3.5 );
-}
-
-void EvtEta2MuMuGamma::init()
-{
- // check that there are 0 arguments
- checkNArg( 0 );
- checkNDaug( 3 );
-
- checkSpinParent( EvtSpinType::SCALAR );
-
- checkSpinDaughter( 0, EvtSpinType::DIRAC );
- checkSpinDaughter( 1, EvtSpinType::DIRAC );
- checkSpinDaughter( 2, EvtSpinType::PHOTON );
-}
-
-void EvtEta2MuMuGamma::decay( EvtParticle* p )
-{
- EvtParticle *ep, *em, *gamma;
- setWeight( p->initializePhaseSpace( getNDaug(), getDaugs(), false,
- 0.00000002, 0, 1 ) );
-
- ep = p->getDaug( 0 );
- em = p->getDaug( 1 );
- gamma = p->getDaug( 2 );
-
- // the next four lines generates events with a weight such that
- // the efficiency for selecting them is good. The parameter below of
- // 0.1 is the size of the peak at low q^2 (in arbitrary units).
- // The value of 0.1 is appropriate for muons.
- // when you use this remember to remove the cut on q^2!
-
- //ep em invariant mass^2
- double m2 = ( ep->getP4() + em->getP4() ).mass2();
- EvtVector4R q = ep->getP4() + em->getP4();
- //Just use the prob summed over spins...
-
- EvtTensor4C w, v;
-
- v = 2.0 * ( gamma->getP4() * q ) *
- EvtGenFunctions::directProd( q, gamma->getP4() ) -
- ( gamma->getP4() * q ) * ( gamma->getP4() * q ) * EvtTensor4C::g() -
- m2 * EvtGenFunctions::directProd( gamma->getP4(), gamma->getP4() );
-
- w = 4.0 * ( EvtGenFunctions::directProd( ep->getP4(), em->getP4() ) +
- EvtGenFunctions::directProd( em->getP4(), ep->getP4() ) -
- EvtTensor4C::g() *
- ( ep->getP4() * em->getP4() - ep->getP4().mass2() ) );
-
- double prob = ( real( cont( v, w ) ) ) / ( m2 * m2 );
- prob *= ( 1.0 / ( ( 0.768 * 0.768 - m2 ) * ( 0.768 * 0.768 - m2 ) +
- 0.768 * 0.768 * 0.151 * 0.151 ) );
-
- // EvtGenReport(EVTGEN_INFO,"EvtGen") << "prob is "<<prob<<endl;
- setProb( prob );
-
- return;
-}
diff --git a/src/EvtGenModels/EvtModelReg.cpp b/src/EvtGenModels/EvtModelReg.cpp
--- a/src/EvtGenModels/EvtModelReg.cpp
+++ b/src/EvtGenModels/EvtModelReg.cpp
@@ -60,7 +60,6 @@
#include "EvtGenModels/EvtDDalitz.hh"
#include "EvtGenModels/EvtDMix.hh"
#include "EvtGenModels/EvtDToKpienu.hh"
-#include "EvtGenModels/EvtEta2MuMuGamma.hh"
#include "EvtGenModels/EvtEtaDalitz.hh"
#include "EvtGenModels/EvtFlatQ2.hh"
#include "EvtGenModels/EvtFlatSqDalitz.hh"
@@ -286,7 +285,6 @@
modelist.registerModel( new EvtDMix );
modelist.registerModel( new EvtD0mixDalitz );
modelist.registerModel( new EvtD0gammaDalitz );
- modelist.registerModel( new EvtEta2MuMuGamma );
modelist.registerModel( new EvtbTosllAli );
modelist.registerModel( new EvtBaryonPCR );
diff --git a/src/EvtGenModels/EvtPi0Dalitz.cpp b/src/EvtGenModels/EvtPi0Dalitz.cpp
--- a/src/EvtGenModels/EvtPi0Dalitz.cpp
+++ b/src/EvtGenModels/EvtPi0Dalitz.cpp
@@ -47,7 +47,36 @@
void EvtPi0Dalitz::initProbMax()
{
- setProbMax( 3.5 );
+ // Search for maximum probability. In order to avoid setting up all
+ // particles with spinors and four-momenta, we use result after all
+ // contractions, which is:
+ // 1/((m_R^2-q^2)^2+m_R^2 Gamma_R^2) 1/(2q^2) (M^2-q^2)^2 beta_l
+ // (1+cos(theta)^2) where we set cos(theta)=1
+ auto daughter1 = getDaug( 0 );
+ auto daughter2 = getDaug( 1 );
+ double q2Min = EvtPDL::getMass( daughter1 ) + EvtPDL::getMass( daughter2 );
+ q2Min *= q2Min;
+ double q2Max = EvtPDL::getMass( getParentId() );
+ q2Max *= q2Max;
+ const int steps = 20000;
+ const double step = ( q2Max - q2Min ) / steps;
+ double maxProb = 0;
+ for ( int ii = 0; ii < steps; ++ii ) {
+ double q2 = q2Min + ii * step;
+ const double mSqDiff = m_m0Sq - q2;
+ const double q2Sq = q2 * q2;
+ double prob = ( q2Max - q2 ) * ( q2Max - q2 ) * ( q2 - q2Min ) /
+ ( q2Sq );
+ prob *= ( 1.0 / ( mSqDiff * mSqDiff + m_m0SqG0Sq ) );
+ // When generating events, we do not start from phase-space, but
+ // add some pole to it, weight of which is taken into account
+ // elsewhere
+ prob /= 1.0 + m_poleSize / ( q2Sq );
+ if ( prob > maxProb ) {
+ maxProb = prob;
+ }
+ }
+ setProbMax( maxProb * 1.05 );
}
void EvtPi0Dalitz::init()
@@ -61,14 +90,19 @@
checkSpinDaughter( 0, EvtSpinType::DIRAC );
checkSpinDaughter( 1, EvtSpinType::DIRAC );
checkSpinDaughter( 2, EvtSpinType::PHOTON );
+
+ // Rescale pole size to improve efficiency. Not sure about exact
+ // factor, but this seem to be best simple rescaling for
+ // eta-->e+e-gamma.
+ const double parentMass = EvtPDL::getMass( getParentId() );
+ m_poleSize *= parentMass * parentMass / ( 0.135 * 0.135 );
}
void EvtPi0Dalitz::decay( EvtParticle* p )
{
EvtParticle *ep, *em, *gamma;
setWeight( p->initializePhaseSpace( getNDaug(), getDaugs(), false,
- 0.00000002, 0, 1 ) );
-
+ m_poleSize, 0, 1 ) );
ep = p->getDaug( 0 );
em = p->getDaug( 1 );
gamma = p->getDaug( 2 );
@@ -97,8 +131,8 @@
( ep->getP4() * em->getP4() - ep->getP4().mass2() ) );
double prob = ( real( cont( v, w ) ) ) / ( m2 * m2 );
- prob *= ( 1.0 / ( ( 0.768 * 0.768 - m2 ) * ( 0.768 * 0.768 - m2 ) +
- 0.768 * 0.768 * 0.151 * 0.151 ) );
+ const double m2Diff = m_m0Sq - m2;
+ prob *= ( 1.0 / ( m2Diff * m2Diff + m_m0SqG0Sq ) );
// EvtGenReport(EVTGEN_INFO,"EvtGen") << "prob is "<<prob<<endl;
setProb( prob );

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