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25 // 25 //
>> 26 //
>> 27 //
>> 28 //
26 // G4 Model: Charge and strangness exchange ba 29 // G4 Model: Charge and strangness exchange based on G4LightMedia model
27 // 28 May 2006 V.Ivanchenko 30 // 28 May 2006 V.Ivanchenko
28 // 31 //
29 // Modified: 32 // Modified:
30 // 07-Jun-06 V.Ivanchenko fix problem of rotat 33 // 07-Jun-06 V.Ivanchenko fix problem of rotation of final state
31 // 25-Jul-06 V.Ivanchenko add 19 MeV low energ 34 // 25-Jul-06 V.Ivanchenko add 19 MeV low energy, below which S-wave is sampled
32 // 12-Jun-12 A.Ribon fix warnings of shadowed 35 // 12-Jun-12 A.Ribon fix warnings of shadowed variables
33 // 06-Aug-15 A.Ribon migrating to G4Exp, G4Log 36 // 06-Aug-15 A.Ribon migrating to G4Exp, G4Log and G4Pow
34 // 37 //
35 38
36 #include "G4ChargeExchange.hh" 39 #include "G4ChargeExchange.hh"
37 #include "G4ChargeExchangeXS.hh" <<
38 #include "G4PhysicalConstants.hh" 40 #include "G4PhysicalConstants.hh"
39 #include "G4SystemOfUnits.hh" 41 #include "G4SystemOfUnits.hh"
40 #include "G4ParticleTable.hh" 42 #include "G4ParticleTable.hh"
41 #include "G4ParticleDefinition.hh" 43 #include "G4ParticleDefinition.hh"
42 #include "G4IonTable.hh" 44 #include "G4IonTable.hh"
43 #include "Randomize.hh" 45 #include "Randomize.hh"
44 #include "G4NucleiProperties.hh" 46 #include "G4NucleiProperties.hh"
45 #include "G4DecayTable.hh" <<
46 #include "G4VDecayChannel.hh" <<
47 #include "G4DecayProducts.hh" <<
48 #include "G4NistManager.hh" <<
49 #include "G4Fragment.hh" <<
50 #include "G4ExcitationHandler.hh" <<
51 #include "G4ReactionProductVector.hh" <<
52 47
53 #include "G4Exp.hh" 48 #include "G4Exp.hh"
54 #include "G4Log.hh" 49 #include "G4Log.hh"
55 #include "G4Pow.hh" 50 #include "G4Pow.hh"
56 51
57 #include "G4HadronicParameters.hh" 52 #include "G4HadronicParameters.hh"
58 #include "G4PhysicsModelCatalog.hh" <<
59 53
60 namespace <<
61 { <<
62 constexpr G4int maxN = 1000; <<
63 constexpr G4double emin = 2*136.9*CLHEP::MeV <<
64 } <<
65 54
66 G4ChargeExchange::G4ChargeExchange(G4ChargeExc << 55 G4ChargeExchange::G4ChargeExchange() : G4HadronicInteraction("Charge Exchange")
67 : G4HadronicInteraction("ChargeExchange"), <<
68 fXSection(ptr), fXSWeightFactor(1.0) <<
69 { 56 {
70 lowEnergyLimit = 1.*CLHEP::MeV; << 57 SetMinEnergy( 0.0*GeV );
71 secID = G4PhysicsModelCatalog::GetModelID( " << 58 SetMaxEnergy( G4HadronicParameters::Instance()->GetMaxEnergy() );
72 nist = G4NistManager::Instance(); << 59
73 fHandler = new G4ExcitationHandler(); << 60 lowestEnergyLimit = 1.*MeV;
74 if (nullptr != fXSection) { << 61
75 fXSWeightFactor = 1.0/fXSection->GetCrossS << 62 theProton = G4Proton::Proton();
76 } << 63 theNeutron = G4Neutron::Neutron();
>> 64 theAProton = G4AntiProton::AntiProton();
>> 65 theANeutron = G4AntiNeutron::AntiNeutron();
>> 66 thePiPlus = G4PionPlus::PionPlus();
>> 67 thePiMinus = G4PionMinus::PionMinus();
>> 68 thePiZero = G4PionZero::PionZero();
>> 69 theKPlus = G4KaonPlus::KaonPlus();
>> 70 theKMinus = G4KaonMinus::KaonMinus();
>> 71 theK0S = G4KaonZeroShort::KaonZeroShort();
>> 72 theK0L = G4KaonZeroLong::KaonZeroLong();
>> 73 theL = G4Lambda::Lambda();
>> 74 theAntiL = G4AntiLambda::AntiLambda();
>> 75 theSPlus = G4SigmaPlus::SigmaPlus();
>> 76 theASPlus = G4AntiSigmaPlus::AntiSigmaPlus();
>> 77 theSMinus = G4SigmaMinus::SigmaMinus();
>> 78 theASMinus = G4AntiSigmaMinus::AntiSigmaMinus();
>> 79 theS0 = G4SigmaZero::SigmaZero();
>> 80 theAS0 = G4AntiSigmaZero::AntiSigmaZero();
>> 81 theXiMinus = G4XiMinus::XiMinus();
>> 82 theXi0 = G4XiZero::XiZero();
>> 83 theAXiMinus = G4AntiXiMinus::AntiXiMinus();
>> 84 theAXi0 = G4AntiXiZero::AntiXiZero();
>> 85 theOmega = G4OmegaMinus::OmegaMinus();
>> 86 theAOmega = G4AntiOmegaMinus::AntiOmegaMinus();
>> 87 theD = G4Deuteron::Deuteron();
>> 88 theT = G4Triton::Triton();
>> 89 theA = G4Alpha::Alpha();
>> 90 theHe3 = G4He3::He3();
77 } 91 }
78 92
79 G4ChargeExchange::~G4ChargeExchange() 93 G4ChargeExchange::~G4ChargeExchange()
80 { << 94 {}
81 delete fHandler; <<
82 } <<
83 95
84 G4HadFinalState* G4ChargeExchange::ApplyYourse 96 G4HadFinalState* G4ChargeExchange::ApplyYourself(
85 const G4HadProjectile& aTrack, G4Nucleus& 97 const G4HadProjectile& aTrack, G4Nucleus& targetNucleus)
86 { 98 {
87 theParticleChange.Clear(); 99 theParticleChange.Clear();
88 auto part = aTrack.GetDefinition(); << 100 const G4HadProjectile* aParticle = &aTrack;
89 G4double ekin = aTrack.GetKineticEnergy(); << 101 G4double ekin = aParticle->GetKineticEnergy();
90 102
91 G4int A = targetNucleus.GetA_asInt(); 103 G4int A = targetNucleus.GetA_asInt();
92 G4int Z = targetNucleus.GetZ_asInt(); 104 G4int Z = targetNucleus.GetZ_asInt();
93 105
94 if (ekin <= lowEnergyLimit) { << 106 if(ekin <= lowestEnergyLimit || A < 3) {
>> 107 theParticleChange.SetEnergyChange(ekin);
>> 108 theParticleChange.SetMomentumChange(0.0,0.0,1.0);
95 return &theParticleChange; 109 return &theParticleChange;
96 } 110 }
97 theParticleChange.SetWeightChange(fXSWeightF <<
98 111
99 G4int projPDG = part->GetPDGEncoding(); << 112 G4double plab = aParticle->GetTotalMomentum();
100 113
101 // for hydrogen targets and positive project <<
102 // is not possible on proton, only on deuter <<
103 if (1 == Z && (211 == projPDG || 321 == proj <<
104 <<
105 if (verboseLevel > 1) 114 if (verboseLevel > 1)
106 G4cout << "G4ChargeExchange for " << part- << 115 G4cout << "G4ChargeExchange::DoIt: Incident particle plab="
>> 116 << plab/GeV << " GeV/c "
>> 117 << " ekin(MeV) = " << ekin/MeV << " "
>> 118 << aParticle->GetDefinition()->GetParticleName() << G4endl;
>> 119
>> 120 // Scattered particle referred to axis of incident particle
>> 121 const G4ParticleDefinition* theParticle = aParticle->GetDefinition();
>> 122
>> 123 G4int N = A - Z;
>> 124 G4int projPDG = theParticle->GetPDGEncoding();
>> 125 if (verboseLevel > 1)
>> 126 G4cout << "G4ChargeExchange for " << theParticle->GetParticleName()
107 << " PDGcode= " << projPDG << " on nucleu 127 << " PDGcode= " << projPDG << " on nucleus Z= " << Z
108 << " A= " << A << " N= " << A - Z << 128 << " A= " << A << " N= " << N
109 << G4endl; 129 << G4endl;
110 130
111 G4double mass1 = G4NucleiProperties::GetNucl << 131 const G4ParticleDefinition* theDef = nullptr;
112 G4LorentzVector lv0 = aTrack.Get4Momentum(); <<
113 G4double etot = mass1 + lv0.e(); <<
114 <<
115 // select final state <<
116 const G4ParticleDefinition* theSecondary = <<
117 fXSection->SampleSecondaryType(part, Z, A) <<
118 G4int pdg = theSecondary->GetPDGEncoding(); <<
119 <<
120 // omega(782) and f2(1270) <<
121 G4bool isShortLived = (pdg == 223 || pdg == <<
122 <<
123 // atomic number of the recoil nucleus <<
124 if (projPDG == -211) { --Z; } <<
125 else if (projPDG == 211) { ++Z; } <<
126 else if (projPDG == -321) { --Z; } <<
127 else if (projPDG == 321) { ++Z; } <<
128 else if (projPDG == 130) { <<
129 if (theSecondary->GetPDGCharge() > 0.0) { <<
130 else { ++Z; } <<
131 } else { <<
132 // not ready for other projectile <<
133 return &theParticleChange; <<
134 } <<
135 132
136 // recoil nucleus << 133 G4double mass2 = G4NucleiProperties::GetNuclearMass(A, Z);
>> 134 G4LorentzVector lv1 = aParticle->Get4Momentum();
>> 135 G4LorentzVector lv0(0.0,0.0,0.0,mass2);
>> 136
>> 137 G4LorentzVector lv = lv0 + lv1;
>> 138 G4ThreeVector bst = lv.boostVector();
>> 139 lv1.boost(-bst);
>> 140 lv0.boost(-bst);
>> 141
>> 142 // Sample final particles
>> 143 G4bool theHyperon = false;
137 const G4ParticleDefinition* theRecoil = null 144 const G4ParticleDefinition* theRecoil = nullptr;
138 if (Z == 0 && A == 1) { theRecoil = G4Neutro << 145 const G4ParticleDefinition* theSecondary = nullptr;
139 else if (Z == 1 && A == 1) { theRecoil = G4P <<
140 else if (Z == 1 && A == 2) { theRecoil = G4D <<
141 else if (Z == 1 && A == 3) { theRecoil = G4T <<
142 else if (Z == 2 && A == 3) { theRecoil = G4H <<
143 else if (Z == 2 && A == 4) { theRecoil = G4A <<
144 else if (nist->GetIsotopeAbundance(Z, A) > 0 <<
145 theRecoil = G4ParticleTable::GetParticleTa <<
146 ->GetIonTable()->GetIon(Z, A, 0.0); <<
147 } <<
148 146
149 // check if there is enough energy for the f << 147 if(theParticle == theProton) {
150 // and sample mass of produced state << 148 theSecondary = theNeutron;
151 const G4double mass0 = theSecondary->GetPDGM << 149 Z++;
152 G4double mass3 = (nullptr == theRecoil) ? << 150 } else if(theParticle == theNeutron) {
153 G4NucleiProperties::GetNuclearMass(A, Z) : << 151 theSecondary = theProton;
154 G4double mass2 = mass0; << 152 Z--;
155 if (isShortLived && << 153 } else if(theParticle == thePiPlus) {
156 !SampleMass(mass2, theSecondary->GetPDGW << 154 theSecondary = thePiZero;
157 return &theParticleChange; << 155 Z++;
>> 156 } else if(theParticle == thePiMinus) {
>> 157 theSecondary = thePiZero;
>> 158 Z--;
>> 159 } else if(theParticle == theKPlus) {
>> 160 if(G4UniformRand()<0.5) theSecondary = theK0S;
>> 161 else theSecondary = theK0L;
>> 162 Z++;
>> 163 } else if(theParticle == theKMinus) {
>> 164 if(G4UniformRand()<0.5) theSecondary = theK0S;
>> 165 else theSecondary = theK0L;
>> 166 Z--;
>> 167 } else if(theParticle == theK0S || theParticle == theK0L) {
>> 168 if(G4UniformRand()*A < G4double(Z)) {
>> 169 theSecondary = theKPlus;
>> 170 Z--;
>> 171 } else {
>> 172 theSecondary = theKMinus;
>> 173 Z++;
>> 174 }
>> 175 } else if(theParticle == theANeutron) {
>> 176 theSecondary = theAProton;
>> 177 Z++;
>> 178 } else if(theParticle == theAProton) {
>> 179 theSecondary = theANeutron;
>> 180 Z--;
>> 181 } else if(theParticle == theL) {
>> 182 G4double x = G4UniformRand();
>> 183 if(G4UniformRand()*A < G4double(Z)) {
>> 184 if(x < 0.2) {
>> 185 theSecondary = theS0;
>> 186 } else if (x < 0.4) {
>> 187 theSecondary = theSPlus;
>> 188 Z--;
>> 189 } else if (x < 0.6) {
>> 190 theSecondary = theProton;
>> 191 theRecoil = theL;
>> 192 theHyperon = true;
>> 193 A--;
>> 194 } else if (x < 0.8) {
>> 195 theSecondary = theProton;
>> 196 theRecoil = theS0;
>> 197 theHyperon = true;
>> 198 A--;
>> 199 } else {
>> 200 theSecondary = theNeutron;
>> 201 theRecoil = theSPlus;
>> 202 theHyperon = true;
>> 203 A--;
>> 204 }
>> 205 } else {
>> 206 if(x < 0.2) {
>> 207 theSecondary = theS0;
>> 208 } else if (x < 0.4) {
>> 209 theSecondary = theSMinus;
>> 210 Z++;
>> 211 } else if (x < 0.6) {
>> 212 theSecondary = theNeutron;
>> 213 theRecoil = theL;
>> 214 A--;
>> 215 theHyperon = true;
>> 216 } else if (x < 0.8) {
>> 217 theSecondary = theNeutron;
>> 218 theRecoil = theS0;
>> 219 theHyperon = true;
>> 220 A--;
>> 221 } else {
>> 222 theSecondary = theProton;
>> 223 theRecoil = theSMinus;
>> 224 theHyperon = true;
>> 225 A--;
>> 226 }
>> 227 }
158 } 228 }
159 229
160 // not possible kinematically << 230 if (Z == 1 && A == 2) theDef = theD;
161 if (etot <= mass2 + mass3) { << 231 else if (Z == 1 && A == 3) theDef = theT;
>> 232 else if (Z == 2 && A == 3) theDef = theHe3;
>> 233 else if (Z == 2 && A == 4) theDef = theA;
>> 234 else {
>> 235 theDef =
>> 236 G4ParticleTable::GetParticleTable()->GetIonTable()->GetIon(Z,A,0.0);
>> 237 }
>> 238 if(!theSecondary) { return &theParticleChange; }
>> 239
>> 240 G4double m11 = theSecondary->GetPDGMass();
>> 241 G4double m21 = theDef->GetPDGMass();
>> 242 if(theRecoil) { m21 += theRecoil->GetPDGMass(); }
>> 243 else { theRecoil = theDef; }
>> 244
>> 245 G4double etot = lv0.e() + lv1.e();
>> 246
>> 247 // kinematiacally impossible
>> 248 if(etot < m11 + m21) {
>> 249 theParticleChange.SetEnergyChange(ekin);
>> 250 theParticleChange.SetMomentumChange(0.0,0.0,1.0);
162 return &theParticleChange; 251 return &theParticleChange;
163 } 252 }
164 253
165 // sample kinematics << 254 G4ThreeVector p1 = lv1.vect();
166 G4LorentzVector lv1(0.0, 0.0, 0.0, mass1); << 255 G4double e1 = 0.5*etot*(1.0 - (m21*m21 - m11*m11)/(etot*etot));
167 G4LorentzVector lv = lv0 + lv1; << 256 // G4double e2 = etot - e1;
168 G4ThreeVector bst = lv.boostVector(); << 257 G4double ptot = std::sqrt(e1*e1 - m11*m11);
169 G4double ss = lv.mag2(); << 258
170 << 259 G4double tmax = 4.0*ptot*ptot;
171 // tmax = 4*momCMS^2 << 260 G4double g2 = GeV*GeV;
172 G4double e2 = ss + mass2*mass2 - mass3*mass3 << 261
173 G4double tmax = e2*e2/ss - 4*mass2*mass2; << 262 G4double t = g2*SampleT(tmax/g2, A);
174 << 263
175 G4double t = SampleT(theSecondary, A, tmax); << 264 if(verboseLevel>1) {
176 << 265 G4cout <<"## G4ChargeExchange t= " << t << " tmax= " << tmax
177 G4double phi = G4UniformRand()*CLHEP::twopi << 266 << " ptot= " << ptot << G4endl;
>> 267 }
>> 268 // Sampling in CM system
>> 269 G4double phi = G4UniformRand()*twopi;
178 G4double cost = 1. - 2.0*t/tmax; 270 G4double cost = 1. - 2.0*t/tmax;
>> 271 if(std::abs(cost) > 1.0) cost = 1.0;
>> 272 G4double sint = std::sqrt((1.0-cost)*(1.0+cost));
179 273
180 if (cost > 1.0) { cost = 1.0; } << 274 //if (verboseLevel > 1)
181 else if(cost < -1.0) { cost = -1.0; } << 275 // G4cout << "cos(t)=" << cost << " std::sin(t)=" << sint << G4endl;
182 276
183 G4double sint = std::sqrt((1.0-cost)*(1.0+co << 277 G4ThreeVector v1(sint*std::cos(phi),sint*std::sin(phi),cost);
>> 278 v1 *= ptot;
>> 279 G4LorentzVector nlv1(v1.x(),v1.y(),v1.z(),e1);
>> 280 G4LorentzVector nlv0 = lv0 + lv1 - nlv1;
184 281
185 if (verboseLevel>1) { << 282 nlv0.boost(bst);
186 G4cout << " t= " << t << " tmax(GeV^2)= " << 283 nlv1.boost(bst);
187 << " cos(t)=" << cost << " sin(t)=" << si <<
188 } <<
189 G4double momentumCMS = 0.5*std::sqrt(tmax); <<
190 G4LorentzVector lv2(momentumCMS*sint*std::co <<
191 momentumCMS*sint*std::sin(phi), <<
192 momentumCMS*cost, <<
193 std::sqrt(momentumCMS*momentumCMS + <<
194 <<
195 // kinematics in the final state, may be a w <<
196 lv2.boost(bst); <<
197 if (lv2.e() < mass2) { <<
198 lv2.setE(mass2); <<
199 } <<
200 lv -= lv2; <<
201 if (lv.e() < mass3) { <<
202 lv.setE(mass3); <<
203 } <<
204 284
205 // prepare secondary particles <<
206 theParticleChange.SetStatusChange(stopAndKil 285 theParticleChange.SetStatusChange(stopAndKill);
207 theParticleChange.SetEnergyChange(0.0); 286 theParticleChange.SetEnergyChange(0.0);
>> 287 G4DynamicParticle * aSec = new G4DynamicParticle(theSecondary, nlv1);
>> 288 theParticleChange.AddSecondary(aSec);
208 289
209 if (!isShortLived) { << 290 G4double erec = std::max(nlv0.e() - m21, 0.0);
210 auto aSec = new G4DynamicParticle(theSecon << 291
211 theParticleChange.AddSecondary(aSec, secID << 292 //G4cout << "erec= " <<erec << " Esec= " << aSec->GetKineticEnergy() << G4endl;
212 } else { <<
213 auto channel = theSecondary->GetDecayTable <<
214 auto products = channel->DecayIt(mass2); <<
215 G4ThreeVector bst1 = lv2.boostVector(); <<
216 G4int N = products->entries(); <<
217 for (G4int i=0; i<N; ++i) { <<
218 auto p = (*products)[i]; <<
219 auto lvp = p->Get4Momentum(); <<
220 lvp.boost(bst1); <<
221 p->Set4Momentum(lvp); <<
222 theParticleChange.AddSecondary(p, secID) <<
223 } <<
224 delete products; <<
225 } <<
226 293
227 // recoil is a stable isotope << 294 if(theHyperon) {
228 if (nullptr != theRecoil) { << 295 theParticleChange.SetLocalEnergyDeposit(erec);
229 auto aRec = new G4DynamicParticle(theRecoi << 296 aSec = new G4DynamicParticle();
230 theParticleChange.AddSecondary(aRec, secID << 297 aSec->SetDefinition(theRecoil);
>> 298 aSec->SetKineticEnergy(0.0);
>> 299 } else if(erec > GetRecoilEnergyThreshold()) {
>> 300 aSec = new G4DynamicParticle(theRecoil, nlv0);
>> 301 theParticleChange.AddSecondary(aSec);
231 } else { 302 } else {
232 // recoil is an unstable fragment << 303 theParticleChange.SetLocalEnergyDeposit(erec);
233 G4Fragment frag(A, Z, lv); <<
234 auto products = fHandler->BreakItUp(frag); <<
235 for (auto & prod : *products) { <<
236 auto dp = new G4DynamicParticle(prod->Ge <<
237 theParticleChange.AddSecondary(dp, secID <<
238 delete prod; <<
239 } <<
240 delete products; <<
241 } 304 }
242 return &theParticleChange; 305 return &theParticleChange;
243 } 306 }
244 307
245 G4double G4ChargeExchange::SampleT(const G4Par << 308 G4double G4ChargeExchange::SampleT(G4double tmax, G4int A)
246 const G4int <<
247 { 309 {
248 G4double aa, bb, cc, dd; 310 G4double aa, bb, cc, dd;
249 G4Pow* g4pow = G4Pow::GetInstance(); 311 G4Pow* g4pow = G4Pow::GetInstance();
250 if (A <= 62.) { 312 if (A <= 62.) {
251 aa = g4pow->powZ(A, 1.63); 313 aa = g4pow->powZ(A, 1.63);
252 bb = 14.5*g4pow->powZ(A, 0.66); 314 bb = 14.5*g4pow->powZ(A, 0.66);
253 cc = 1.4*g4pow->powZ(A, 0.33); 315 cc = 1.4*g4pow->powZ(A, 0.33);
254 dd = 10.; 316 dd = 10.;
255 } else { 317 } else {
256 aa = g4pow->powZ(A, 1.33); 318 aa = g4pow->powZ(A, 1.33);
257 bb = 60.*g4pow->powZ(A, 0.33); 319 bb = 60.*g4pow->powZ(A, 0.33);
258 cc = 0.4*g4pow->powZ(A, 0.40); 320 cc = 0.4*g4pow->powZ(A, 0.40);
259 dd = 10.; 321 dd = 10.;
260 } 322 }
261 G4double x1 = (1.0 - G4Exp(-tmax*bb))*aa/bb; 323 G4double x1 = (1.0 - G4Exp(-tmax*bb))*aa/bb;
262 G4double x2 = (1.0 - G4Exp(-tmax*dd))*cc/dd; 324 G4double x2 = (1.0 - G4Exp(-tmax*dd))*cc/dd;
263 325
264 G4double t; 326 G4double t;
265 G4double y = bb; 327 G4double y = bb;
266 if(G4UniformRand()*(x1 + x2) < x2) y = dd; 328 if(G4UniformRand()*(x1 + x2) < x2) y = dd;
267 329
268 for (G4int i=0; i<maxN; ++i) { << 330 const G4int maxNumberOfLoops = 10000;
>> 331 G4int loopCounter = 0;
>> 332 do {
269 t = -G4Log(G4UniformRand())/y; 333 t = -G4Log(G4UniformRand())/y;
270 if (t <= tmax) { return t; } << 334 } while ( (t > tmax) &&
>> 335 ++loopCounter < maxNumberOfLoops ); /* Loop checking, 10.08.2015, A.Ribon */
>> 336 if ( loopCounter >= maxNumberOfLoops ) {
>> 337 t = 0.0;
271 } 338 }
272 return 0.0; << 339 return t;
273 } 340 }
274 341
275 G4bool G4ChargeExchange::SampleMass(G4double& <<
276 { <<
277 // +- 4 width but above 2 pion mass <<
278 const G4double e1 = std::max(M - 4*G, emin); <<
279 const G4double e2 = std::min(M + 4*G, elim) <<
280 if (e2 <= 0.0) { return false; } <<
281 const G4double M2 = M*M; <<
282 const G4double MG2 = M2*G*G; <<
283 <<
284 // sampling Breit-Wigner function <<
285 for (G4int i=0; i<maxN; ++i) { <<
286 G4double e = e1 + e2*G4UniformRand(); <<
287 G4double x = e*e - M2; <<
288 G4double y = MG2/(x*x + MG2); <<
289 if (y >= G4UniformRand()) { <<
290 M = e; <<
291 return true; <<
292 } <<
293 } <<
294 return false; <<
295 } <<
296 342