coverity fix
[u/mrichter/AliRoot.git] / EVGEN / AliGenDeuteron.cxx
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15
16 //////////////////////////////////////////////////////////////////////////
17 // Afterburner to generate (anti)deuterons simulating coalescence of
18 // (anti)nucleons as in A. J. Baltz et al., Phys. lett B 325(1994)7.
19 // If the nucleon generator does not provide a spatial description of 
20 // the source the afterburner can provide one.
21 //
22 // There two options for the source: a thermal picture where all nucleons
23 // are placed randomly and homogeneously in an spherical volume, or
24 // an expansion one where they are projected onto its surface.
25 //
26 // An (anti)deuteron will form if there is a pair of (anti)proton-(anti)neutron
27 // with momentum difference less than ~ 300MeV and relative distance less than
28 // ~ 2.1fm. Only 3/4 of these clusters are accepted due to the deuteron spin.
29 //
30 // When there are more than one pair fulfilling the coalescence conditions,
31 // the selected pair can be the one with the first partner, with
32 // the lowest relative momentum, the lowest relative distance or both.
33 //////////////////////////////////////////////////////////////////////////
34
35 // Author: Eulogio Serradilla <eulogio.serradilla@ciemat.es>,
36 //         Arturo Menchaca <menchaca@fisica.unam.mx>
37 //
38
39 #include "Riostream.h"
40 #include "TParticle.h"
41 #include "AliRun.h"
42 #include "AliStack.h"
43 #include "TMath.h"
44 #include "TMCProcess.h"
45 #include "TList.h"
46 #include "TVector3.h"
47 #include "AliMC.h"
48 #include "TArrayF.h"
49 #include "AliCollisionGeometry.h"
50 #include "AliGenCocktailEventHeader.h"
51 #include "AliGenCocktailEntry.h"
52 #include "AliGenCocktailAfterBurner.h"
53 #include "AliGenDeuteron.h"
54
55 ClassImp(AliGenDeuteron)
56
57 AliGenDeuteron::AliGenDeuteron(Int_t sign, Double_t pmax, Double_t rmax, Int_t cluster)
58  :fSign(1)
59  ,fPmax(pmax)
60  ,fRmax(rmax)
61  ,fSpinProb(0.75)
62  ,fMaxRadius(1000.)
63  ,fClusterType(cluster)
64  ,fModel(0)
65  ,fTimeLength(2.5)
66  ,fB(0)
67  ,fR(0)
68  ,fPsiR(0)
69  ,fCurStack(0)
70  ,fNtrk(0)
71 {
72 //
73 // constructor
74 //
75         fSign = sign > 0 ? 1:-1;
76         
77 }
78
79 AliGenDeuteron::~AliGenDeuteron()
80 {
81 //
82 // Default destructor
83 //
84 }
85
86 void AliGenDeuteron::Init()
87 {
88 //
89 // Standard AliGenerator initializer
90 //
91 }
92
93 void AliGenDeuteron::Generate()
94 {
95 //
96 // Look for coalescence of (anti)nucleons in the nucleon source
97 // provided by the generator cocktail
98 //
99         AliInfo(Form("sign: %d, Pmax: %g GeV/c, Rmax: %g fm, cluster: %d",fSign, fPmax, fRmax, fClusterType));
100         if(fModel!=kNone) AliInfo(Form("model: %d, time: %g fm/c", fModel, fTimeLength));
101         
102         AliGenCocktailAfterBurner* gener = (AliGenCocktailAfterBurner*)gAlice->GetMCApp()->Generator();
103         
104         // find nuclear radius, only for first generator and projectile=target
105         Bool_t collisionGeometry=0;
106         if(fModel != kNone && gener->FirstGenerator()->Generator()->ProvidesCollisionGeometry())
107         {
108                 TString name;
109                 Int_t ap, zp, at, zt;
110                 gener->FirstGenerator()->Generator()->GetProjectile(name,ap,zp);
111                 gener->FirstGenerator()->Generator()->GetTarget(name,at,zt);
112                 if(ap != at) AliWarning("projectile and target have different size");
113                 fR = 1.29*TMath::Power(at, 1./3.);
114                 collisionGeometry = 1;
115         }
116         
117         for(Int_t ns = 0; ns < gener->GetNumberOfEvents(); ++ns)
118         {
119                 gener->SetActiveEventNumber(ns);
120                 
121                 if(fModel != kNone && collisionGeometry)
122                 {
123                         fPsiR = (gener->GetCollisionGeometry(ns))->ReactionPlaneAngle();
124                         fB = (gener->GetCollisionGeometry(ns))->ImpactParameter();
125                         
126                         if(fB >= 2.*fR) continue; // no collision
127                 }
128                 
129                 // primary vertex
130                 TArrayF primVtx;
131                 gener->GetActiveEventHeader()->PrimaryVertex(primVtx);
132                 TVector3 r0(primVtx[0],primVtx[1],primVtx[2]);
133                 
134                 // emerging nucleons from the collision
135                 fCurStack = gener->GetStack(ns);
136                 if(!fCurStack)
137                 {
138                         AliWarning("no event stack");
139                         return;
140                 }
141                 
142                 TList* protons = new TList();
143                 protons->SetOwner(kFALSE);
144                 TList* neutrons = new TList();
145                 neutrons->SetOwner(kFALSE);
146                 
147                 for (Int_t i=0; i < fCurStack->GetNtrack(); ++i)
148                 {
149                         TParticle* iParticle = fCurStack->Particle(i);
150                         
151                         if(iParticle->TestBit(kDoneBit)) continue;
152                         
153                         // select only nucleons within the freeze-out volume
154                         TVector3 r(iParticle->Vx(),iParticle->Vy(),iParticle->Vz());
155                         if((r-r0).Mag() > fMaxRadius*1.e-13) continue;
156                         
157                         Int_t pdgCode = iParticle->GetPdgCode();
158                         if(pdgCode == fSign*2212)// (anti)proton
159                         {
160                                 FixProductionVertex(iParticle);
161                                 protons->Add(iParticle);
162                         }
163                         else if(pdgCode == fSign*2112) // (anti)neutron
164                         {
165                                 FixProductionVertex(iParticle);
166                                 neutrons->Add(iParticle);
167                         }
168                 }
169                 
170                 // look for clusters
171                 if(fClusterType==kFirstPartner)
172                 {
173                         FirstPartner(protons, neutrons);
174                 }
175                 else
176                 {
177                         WeightMatrix(protons, neutrons);
178                 }
179                 
180                 protons->Clear("nodelete");
181                 neutrons->Clear("nodelete");
182                 
183                 delete protons;
184                 delete neutrons;
185         }
186         
187         AliInfo("DONE");
188 }
189
190 Double_t AliGenDeuteron::GetCoalescenceProbability(const TParticle* nucleon1, const TParticle* nucleon2) const
191 {
192 //
193 // Coalescence conditions as in
194 // A. J. Baltz et al., Phys. lett B 325(1994)7
195 //
196 // returns < 0 if coalescence is not possible
197 // otherwise returns a coalescence probability
198 //
199         TVector3 v1(nucleon1->Vx(), nucleon1->Vy(), nucleon1->Vz());
200         TVector3 p1(nucleon1->Px(), nucleon1->Py(), nucleon1->Pz());
201         
202         TVector3 v2(nucleon2->Vx(), nucleon2->Vy(), nucleon2->Vz());
203         TVector3 p2(nucleon2->Px(), nucleon2->Py(), nucleon2->Pz());
204         
205         Double_t deltaP = (p2-p1).Mag();       // relative momentum
206         if( deltaP >= fPmax)       return -1.;
207         
208         Double_t deltaR = (v2-v1).Mag();       // relative distance (cm)
209         if(deltaR >= fRmax*1.e-13) return -1.;
210         
211         if(Rndm() > fSpinProb)    return -1.;  // spin
212         
213         if(fClusterType == kLowestMomentum) return 1. - deltaP/fPmax;
214         if(fClusterType == kLowestDistance) return 1. - 1.e+13*deltaR/fRmax;
215         
216         return 1. - 1.e+13*(deltaP*deltaR)/(fRmax*fPmax);
217 }
218
219 void AliGenDeuteron::FirstPartner(const TList* protons, TList* neutrons)
220 {
221 //
222 // Clusters are made with the first nucleon pair that fulfill
223 // the coalescence conditions, starting with the protons
224 //
225         TIter p_next(protons);
226         while(TParticle* n0 = (TParticle*) p_next())
227         {
228                 TParticle* partner = 0;
229                 TIter n_next(neutrons);
230                 while(TParticle* n1 = (TParticle*) n_next() )
231                 {
232                         if(GetCoalescenceProbability(n0, n1) < 0 ) continue; // with next neutron
233                         partner = n1;
234                         break;
235                 }
236                 
237                 if(partner == 0) continue; // with next proton
238                 
239                 PushDeuteron(n0, partner);
240                 
241                 // Remove from the list for the next iteration
242                 neutrons->Remove(partner);
243         }
244 }
245
246 void AliGenDeuteron::WeightMatrix(const TList* protons, const TList* neutrons)
247 {
248 //
249 // Build all possible nucleon pairs with their own probability
250 // and select only those with the highest coalescence probability
251 //
252         Int_t nMaxPairs = protons->GetSize()*neutrons->GetSize();
253         
254         TParticle** cProton = new TParticle*[nMaxPairs];
255         TParticle** cNeutron = new TParticle*[nMaxPairs];
256         Double_t*  cWeight = new Double_t[nMaxPairs];
257         
258         // build all pairs with probability > 0
259         Int_t cIdx = -1;
260         TIter p_next(protons);
261         while(TParticle* n1 = (TParticle*) p_next())
262         {
263                 TIter n_next(neutrons);
264                 while(TParticle* n2 = (TParticle*) n_next() )
265                 {
266                         Double_t weight = this->GetCoalescenceProbability(n1,n2);
267                         if(weight < 0) continue;
268                         ++cIdx;
269                         cProton[cIdx]  = n1;
270                         cNeutron[cIdx] = n2;
271                         cWeight[cIdx]  = weight;
272                 }
273                 n_next.Reset();
274         }
275         p_next.Reset();
276         
277         Int_t nPairs = cIdx + 1;
278         
279         // find the interacting pairs:
280         // remove repeated pairs and select only
281         // the pair with the highest coalescence probability
282         
283         Int_t nMaxIntPair = TMath::Min(protons->GetSize(), neutrons->GetSize());
284         
285         TParticle** iProton = new TParticle*[nMaxIntPair];
286         TParticle** iNeutron = new TParticle*[nMaxIntPair];
287         Double_t* iWeight = new Double_t[nMaxIntPair];
288         
289         Int_t iIdx = -1;
290         while(true)
291         {
292                 Int_t j = -1;
293                 Double_t wMax = 0;
294                 for(Int_t i=0; i < nPairs; ++i)
295                 {
296                         if(cWeight[i] > wMax)
297                         {
298                                 wMax=cWeight[i];
299                                 j = i;
300                         }
301                 }
302                 
303                 if(j == -1 ) break; // end
304                 
305                 // Save the interacting pair
306                 ++iIdx;
307                 iProton[iIdx]  = cProton[j];
308                 iNeutron[iIdx] = cNeutron[j];
309                 iWeight[iIdx]  = cWeight[j];
310                 
311                 // invalidate all combinations with these pairs for the next iteration
312                 for(Int_t i=0; i < nPairs; ++i)
313                 {
314                         if(cProton[i] == iProton[iIdx]) cWeight[i] = -1.;
315                         if(cNeutron[i] == iNeutron[iIdx]) cWeight[i] = -1.;
316                 }
317         }
318         
319         Int_t nIntPairs = iIdx + 1;
320         
321         delete[] cProton;
322         delete[] cNeutron;
323         delete[] cWeight;
324         
325         // Add the (anti)deuterons to the current event stack
326         for(Int_t i=0; i<nIntPairs; ++i)
327         {
328                 TParticle* n1 = iProton[i];
329                 TParticle* n2 = iNeutron[i];
330                 PushDeuteron(n1,n2);
331         }
332         
333         delete[] iProton;
334         delete[] iNeutron;
335         delete[] iWeight;
336 }
337
338 void AliGenDeuteron::PushDeuteron(TParticle* parent1, TParticle* parent2)
339 {
340 //
341 // Create an (anti)deuteron from parent1 and parent2,
342 // add to the current stack and set kDoneBit for the parents
343 //
344         const Double_t kDeuteronMass = 1.87561282;
345         const Int_t kDeuteronPdg = 1000010020;
346         
347         // momentum
348         TVector3 p1(parent1->Px(), parent1->Py(), parent1->Pz());
349         TVector3 p2(parent2->Px(), parent2->Py(), parent2->Pz());
350         TVector3 pN = p1+p2;
351         
352         // production vertex same as the parent1's
353         TVector3 vN(parent1->Vx(), parent1->Vy(), parent1->Vz());
354         
355         // E^2 = p^2 + m^2
356         Double_t energy = TMath::Sqrt(pN.Mag2() + kDeuteronMass*kDeuteronMass);
357         
358         // Add a new (anti)deuteron to current event stack
359         fCurStack->PushTrack(1, fCurStack->Particles()->IndexOf(parent1), fSign*kDeuteronPdg,
360                          pN.X(), pN.Y(), pN.Z(), energy,
361                          vN.X(), vN.Y(), vN.Z(), parent1->T(),
362                          0., 0., 0., kPNCapture, fNtrk, 1., 0);
363         
364         // Set kDoneBit for the parents
365         parent1->SetBit(kDoneBit);
366         parent2->SetBit(kDoneBit);
367 }
368
369 void AliGenDeuteron::FixProductionVertex(TParticle* i)
370 {
371 //
372 // Replace current generator nucleon spatial distribution
373 // with a custom distribution according to the selected model
374 //
375         if(fModel == kNone || fModel > kExpansion) return;
376         
377         // semi-axis from collision geometry (fm)
378         Double_t a = fTimeLength + TMath::Sqrt(fR*fR - fB*fB/4.);
379         Double_t b = fTimeLength + fR - fB/2.;
380         Double_t c = fTimeLength;
381         
382         Double_t xx = 0;
383         Double_t yy = 0;
384         Double_t zz = 0;
385         
386         if(fModel == kThermal)
387         {
388                 // uniformly ditributed in the volume on an ellipsoid
389                 // random (r,theta,phi) unit sphere
390                 Double_t r = TMath::Power(Rndm(),1./3.);
391                 Double_t theta = TMath::ACos(2.*Rndm()-1.);
392                 Double_t phi = 2.*TMath::Pi()*Rndm();
393                 
394                 // transform coordenates
395                 xx = a*r*TMath::Sin(theta)*TMath::Cos(phi);
396                 yy = b*r*TMath::Sin(theta)*TMath::Sin(phi);
397                 zz = c*r*TMath::Cos(theta);
398         }
399         else if(fModel == kExpansion)
400         {
401                 // project into the surface of an ellipsoid
402                 xx = a*TMath::Sin(i->Theta())*TMath::Cos(i->Phi());
403                 yy = b*TMath::Sin(i->Theta())*TMath::Sin(i->Phi());
404                 zz = c*TMath::Cos(i->Theta());
405         }
406         
407         // rotate by the reaction plane angle
408         Double_t x = xx*TMath::Cos(fPsiR)+yy*TMath::Sin(fPsiR);
409         Double_t y = -xx*TMath::Sin(fPsiR)+yy*TMath::Cos(fPsiR);
410         Double_t z = zz;
411         
412         // translate by the production vertex (cm)
413         i->SetProductionVertex(i->Vx() + 1.e-13*x, i->Vy() + 1.e-13*y, i->Vz() + 1.e-13*z, i->T());
414 }
415