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25 //
26 // INCL++ intra-nuclear cascade model
27 // Alain Boudard, CEA-Saclay, France
28 // Joseph Cugnon, University of Liege, Belgium
29 // Jean-Christophe David, CEA-Saclay, France
30 // Pekka Kaitaniemi, CEA-Saclay, France, and Helsinki Institute of Physics, Finland
31 // Sylvie Leray, CEA-Saclay, France
32 // Davide Mancusi, CEA-Saclay, France
33 //
34 #define INCLXX_IN_GEANT4_MODE 1
35
36 #include "globals.hh"
37
38 #include "G4INCLPiNToEtaChannel.hh"
39 #include "G4INCLKinematicsUtils.hh"
40 #include "G4INCLBinaryCollisionAvatar.hh"
41 #include "G4INCLRandom.hh"
42 #include "G4INCLGlobals.hh"
43 #include "G4INCLLogger.hh"
44
45 namespace G4INCL {
46
47 PiNToEtaChannel::PiNToEtaChannel(Particle *p1, Particle *p2)
48 : particle1(p1), particle2(p2)
49 {
50
51 }
52
53 PiNToEtaChannel::~PiNToEtaChannel(){
54
55 }
56
57 void PiNToEtaChannel::fillFinalState(FinalState *fs) {
58 Particle * nucleon;
59 Particle * pion;
60 if(particle1->isNucleon()) {
61 nucleon = particle1;
62 pion = particle2;
63 } else {
64 nucleon = particle2;
65 pion = particle1;
66 }
67
68 G4int iso=ParticleTable::getIsospin(nucleon->getType())+ParticleTable::getIsospin(pion->getType());
69 // assert(iso == 1 || iso == -1);
70 if (iso == 1) {
71 nucleon->setType(Proton);
72 }
73 else if (iso == -1) {
74 nucleon->setType(Neutron);
75 }
76 pion->setType(Eta);
77 #ifdef INCLXX_IN_GEANT4_MODE
78 // Erase the parent resonance information of the nucleon and pion
79 nucleon->setParentResonancePDGCode(0);
80 nucleon->setParentResonanceID(0);
81 pion->setParentResonancePDGCode(0);
82 pion->setParentResonanceID(0);
83 #endif
84 G4double sh=nucleon->getEnergy()+pion->getEnergy();
85 G4double mn=nucleon->getMass();
86 G4double me=pion->getMass();
87 G4double en=(sh*sh+mn*mn-me*me)/(2*sh);
88 nucleon->setEnergy(en);
89 G4double ee=std::sqrt(en*en-mn*mn+me*me);
90 pion->setEnergy(ee);
91 G4double pn=std::sqrt(en*en-mn*mn);
92
93 // real distribution (from PRC 78, 025204 (2008))
94
95 G4double ECM=G4INCL::KinematicsUtils::totalEnergyInCM(particle1,particle2);
96
97 const G4double pi=std::acos(-1.0);
98 G4double x1;
99 G4double u1;
100 G4double fteta;
101 G4double teta;
102 G4double fi;
103
104 if (ECM < 1650.) {
105 // below 1650 MeV - angular distribution (x=cos(theta): ax^2+bx+c
106
107 G4double f1= -0.0000288627*ECM*ECM+0.09155289*ECM-72.25436; // f(1) that is the maximum (fit on experimental data)
108 G4double b1=(f1-(f1/(1.5-0.5*std::pow((ECM-1580.)/95.,2))))/2.; // ideas: 1) f(-1)=0.5f(1); 2) "power term" flattens the distribution away from ECM=1580 MeV
109 G4double a1=2.5*b1; // minimum at cos(theta) = -0.2
110 G4double c1=f1-3.5*b1;
111
112 G4double interg1=2.*a1/3. +2.*c1; // (integral to normalize)
113
114 G4int passe1=0;
115 while (passe1==0) {
116 // Sample x from -1 to 1
117 x1=Random::shoot();
118 if (Random::shoot() > 0.5) x1=-x1;
119
120 // Sample u from 0 to 1
121 u1=Random::shoot();
122 fteta=(a1*x1*x1+b1*x1+c1)/interg1;
123 // The condition
124 if (u1*f1/interg1 < fteta) {
125 teta=std::acos(x1);
126 passe1=1;
127 }
128 }
129 }
130 else {
131 // above 1650 MeV - angular distribution (x=cos(theta): (ax^2+bx+c)*(0.5+(arctan(10*(x+dev)))/pi) + vert
132
133 G4double a2=-0.29;
134 G4double b2=0.348; // ax^2+bx+c: around cos(theta)=0.6 with maximum at 0.644963 (value = 0.1872666)
135 G4double c2=0.0546;
136 G4double dev=-0.2; // tail close to zero from "dev" down to -1
137 G4double vert=0.04; // to avoid negative differential cross sections
138
139 G4double interg2=0.1716182902205207; // with the above given parameters! (integral to normalize)
140 const G4double f2=1.09118088; // maximum (integral taken into account)
141
142 G4int passe2=0;
143 while (passe2==0) {
144 // Sample x from -1 to 1
145 x1=Random::shoot();
146 if (Random::shoot() > 0.5) x1=-x1;
147
148 // Sample u from 0 to 1
149 u1=Random::shoot();
150 fteta=((a2*x1*x1+b2*x1+c2)*(0.5+(std::atan(10*(x1+dev)))/pi) + vert)/interg2;
151 // The condition
152 if (u1*f2 < fteta) {
153 teta=std::acos(x1);
154 passe2=1;
155 }
156 }
157 }
158
159 fi=(2.0*pi)*Random::shoot();
160
161 ThreeVector mom_nucleon(
162 pn*std::sin(teta)*std::cos(fi),
163 pn*std::sin(teta)*std::sin(fi),
164 pn*std::cos(teta)
165 );
166 // end real distribution
167
168 nucleon->setMomentum(-mom_nucleon);
169 pion->setMomentum(mom_nucleon);
170
171 fs->addModifiedParticle(nucleon);
172 fs->addModifiedParticle(pion);
173 }
174
175 }
176