Geant4  10.00.p02
G4SingleDiffractiveExcitation.cc
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27 // $Id: G4SingleDiffractiveExcitation.cc 69570 2013-05-08 13:23:39Z gcosmo $
28 // ------------------------------------------------------------
29 // GEANT 4 class implemetation file
30 //
31 // ---------------- G4SingleDiffractiveExcitation --------------
32 // by Gunter Folger, October 1998.
33 // diffractive Excitation used by strings models
34 // Take a projectile and a target
35 // excite the projectile and target
36 // ------------------------------------------------------------
37 
39 #include "globals.hh"
40 #include "G4PhysicalConstants.hh"
41 #include "G4SystemOfUnits.hh"
42 #include "Randomize.hh"
43 #include "G4LorentzRotation.hh"
44 #include "G4ThreeVector.hh"
45 #include "G4ParticleDefinition.hh"
46 #include "G4VSplitableHadron.hh"
47 #include "G4ExcitedString.hh"
48 
50 :
51 widthOfPtSquare(-2*sqr(sigmaPt)) , minExtraMass(minextraMass),
52 minmass(x0mass)
53 {}
54 
56 {}
57 
60 {
61 
62  G4LorentzVector Pprojectile=projectile->Get4Momentum();
63  G4double Mprojectile2=sqr(projectile->GetDefinition()->GetPDGMass() + minExtraMass);
64 
65  G4LorentzVector Ptarget=target->Get4Momentum();
66  G4double Mtarget2=sqr(target->GetDefinition()->GetPDGMass() + minExtraMass);
67  // G4cout << "E proj, target :" << Pprojectile.e() << ", " <<
68  // Ptarget.e() << G4endl;
69 
70  G4bool KeepProjectile= G4UniformRand() > 0.5;
71 
72  // reset the min.mass of the non diffractive particle to its value, ( minus a bit for rounding...)
73  if ( KeepProjectile )
74  {
75  // cout << " Projectile fix" << G4endl;
76  Mprojectile2 = sqr(projectile->GetDefinition()->GetPDGMass() * (1-perCent) );
77  } else {
78  // cout << " Target fix" << G4endl;
79  Mtarget2=sqr(target->GetDefinition()->GetPDGMass() * (1-perCent) );
80  }
81 
82  // Transform momenta to cms and then rotate parallel to z axis;
83 
84  G4LorentzVector Psum;
85  Psum=Pprojectile+Ptarget;
86 
87  G4LorentzRotation toCms(-1*Psum.boostVector());
88 
89  G4LorentzVector Ptmp=toCms*Pprojectile;
90 
91  if ( Ptmp.pz() <= 0. )
92  {
93  // "String" moving backwards in CMS, abort collision !!
94  // G4cout << " abort Collision!! " << G4endl;
95  return false;
96  }
97 
98  toCms.rotateZ(-1*Ptmp.phi());
99  toCms.rotateY(-1*Ptmp.theta());
100 
101  // G4cout << "Pprojectile be4 boost " << Pprojectile << G4endl;
102  // G4cout << "Ptarget be4 boost : " << Ptarget << G4endl;
103 
104 
105 
106  G4LorentzRotation toLab(toCms.inverse());
107 
108  Pprojectile.transform(toCms);
109  Ptarget.transform(toCms);
110 
111  G4LorentzVector Qmomentum;
112  G4int whilecount=0;
113  do {
114  // Generate pt
115 
116  G4double maxPtSquare=sqr(Ptarget.pz());
117  if (whilecount++ >= 500 && (whilecount%100)==0)
118  // G4cout << "G4SingleDiffractiveExcitation::ExciteParticipants possibly looping"
119  // << ", loop count/ maxPtSquare : "
120  // << whilecount << " / " << maxPtSquare << G4endl;
121  if (whilecount > 1000 )
122  {
123  Qmomentum=G4LorentzVector(0.,0.,0.,0.);
124  // G4cout << "G4SingleDiffractiveExcitation::ExciteParticipants: Aborting loop!" << G4endl;
125  return false; // Ignore this interaction
126  }
127  Qmomentum=G4LorentzVector(GaussianPt(widthOfPtSquare,maxPtSquare),0);
128 
129 
130  // Momentum transfer
131  G4double Xmin = minmass / ( Pprojectile.e() + Ptarget.e() );
132  G4double Xmax=1.;
133  G4double Xplus =ChooseX(Xmin,Xmax);
134  G4double Xminus=ChooseX(Xmin,Xmax);
135 
136  G4double pt2=G4ThreeVector(Qmomentum.vect()).mag2();
137  G4double Qplus =-1 * pt2 / Xminus/Ptarget.minus();
138  G4double Qminus= pt2 / Xplus /Pprojectile.plus();
139 
140  if ( KeepProjectile )
141  {
142  Qminus = (sqr(projectile->GetDefinition()->GetPDGMass()) + pt2 )
143  / (Pprojectile.plus() + Qplus )
144  - Pprojectile.minus();
145  } else
146  {
147  Qplus = Ptarget.plus()
148  - (sqr(target->GetDefinition()->GetPDGMass()) + pt2 )
149  / (Ptarget.minus() - Qminus );
150  }
151 
152  Qmomentum.setPz( (Qplus-Qminus)/2 );
153  Qmomentum.setE( (Qplus+Qminus)/2 );
154 
155  // G4cout << "Qplus / Qminus " << Qplus << " / " << Qminus<<G4endl;
156  // G4cout << "pt2 " << pt2 << G4endl;
157  // G4cout << "Qmomentum " << Qmomentum << G4endl;
158  // G4cout << " Masses (P/T) : " << (Pprojectile+Qmomentum).mag() <<
159  // " / " << (Ptarget-Qmomentum).mag() << G4endl;
160 
161  } while ( (Ptarget-Qmomentum).mag2() <= Mtarget2
162  || (Pprojectile+Qmomentum).mag2() <= Mprojectile2
163  || (Ptarget-Qmomentum).e() < 0.
164  || (Pprojectile+Qmomentum).e() < 0. );
165 
166 
167  // G4double Ecms=Pprojectile.e() + Ptarget.e();
168 
169  Pprojectile += Qmomentum;
170 
171  Ptarget -= Qmomentum;
172 
173  // G4cout << "Pprojectile.e() : " << Pprojectile.e() << G4endl;
174  // G4cout << "Ptarget.e() : " << Ptarget.e() << G4endl;
175 
176  // G4cout << "end event_______________________________________________"<<G4endl;
177  //
178 
179 
180  // G4cout << "Pprojectile with Q : " << Pprojectile << G4endl;
181  // G4cout << "Ptarget with Q : " << Ptarget << G4endl;
182  // G4cout << "Projectile back: " << toLab * Pprojectile << G4endl;
183  // G4cout << "Target back: " << toLab * Ptarget << G4endl;
184 
185  // Transform back and update SplitableHadron Participant.
186  Pprojectile.transform(toLab);
187  Ptarget.transform(toLab);
188 
189  // G4cout << "G4SingleDiffractiveExcitation- Target mass " << Ptarget.mag() << G4endl;
190  // G4cout << "G4SingleDiffractiveExcitation- Projectile mass " << Pprojectile.mag() << G4endl;
191 
192  target->Set4Momentum(Ptarget);
193  projectile->Set4Momentum(Pprojectile);
194 
195 
196  return true;
197 }
198 
199 
200 
201 
202 // --------- private methods ----------------------
203 
205 {
206  // choose an x between Xmin and Xmax with P(x) ~ 1/x
207 
208  // to be improved...
209 
210  G4double range=Xmax-Xmin;
211 
212  if ( Xmin <= 0. || range <=0. )
213  {
214  G4cout << " Xmin, range : " << Xmin << " , " << range << G4endl;
215  throw G4HadronicException(__FILE__, __LINE__, "G4SingleDiffractiveExcitation::ChooseX : Invalid arguments ");
216  }
217 
218  G4double x;
219  do {
220  x=Xmin + G4UniformRand() * range;
221  } while ( Xmin/x < G4UniformRand() );
222 
223  // cout << "DiffractiveX "<<x<<G4endl;
224  return x;
225 }
226 
228 { // @@ this method is used in FTFModel as well. Should go somewhere common!
229 
230  G4double pt2;
231 
232  do {
233  pt2=widthSquare * std::log( G4UniformRand() );
234  } while ( pt2 > maxPtSquare);
235 
236  pt2=std::sqrt(pt2);
237 
238  G4double phi=G4UniformRand() * twopi;
239 
240  return G4ThreeVector (pt2*std::cos(phi), pt2*std::sin(phi), 0.);
241 }
242 
243 
244 
245 
246 
G4bool ExciteParticipants(G4VSplitableHadron *aPartner, G4VSplitableHadron *bPartner) const
G4double ChooseX(G4double Xmin, G4double Xmax) const
CLHEP::Hep3Vector G4ThreeVector
CLHEP::HepLorentzRotation G4LorentzRotation
int G4int
Definition: G4Types.hh:78
G4ParticleDefinition * GetDefinition() const
#define G4UniformRand()
Definition: Randomize.hh:87
G4GLOB_DLL std::ostream G4cout
bool G4bool
Definition: G4Types.hh:79
static const double perCent
Definition: G4SIunits.hh:296
const G4LorentzVector & Get4Momentum() const
G4double GetPDGMass() const
G4SingleDiffractiveExcitation(G4double sigmaPt=0.6 *CLHEP::GeV, G4double minExtraMass=250 *CLHEP::MeV, G4double x0mass=250 *CLHEP::MeV)
G4ThreeVector GaussianPt(G4double widthSquare, G4double maxPtSquare) const
#define G4endl
Definition: G4ios.hh:61
void Set4Momentum(const G4LorentzVector &a4Momentum)
T sqr(const T &x)
Definition: templates.hh:145
double G4double
Definition: G4Types.hh:76
CLHEP::HepLorentzVector G4LorentzVector