1 /**************************************************************************
2 * Copyright(c) 2009-2010, ALICE Experiment at CERN, All rights reserved. *
4 * Author: The ALICE Off-line Project. *
5 * Contributors are mentioned in the code where appropriate. *
7 * Permission to use, copy, modify and distribute this software and its *
8 * documentation strictly for non-commercial purposes is hereby granted *
9 * without fee, provided that the above copyright notice appears in all *
10 * copies and that both the copyright notice and this permission notice *
11 * appear in the supporting documentation. The authors make no claims *
12 * about the suitability of this software for any purpose. It is *
13 * provided "as is" without express or implied warranty. *
14 **************************************************************************/
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.
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.
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.
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 //////////////////////////////////////////////////////////////////////////
35 // Author: Eulogio Serradilla <eulogio.serradilla@ciemat.es>,
36 // Arturo Menchaca <menchaca@fisica.unam.mx>
39 #include "Riostream.h"
40 #include "TParticle.h"
44 #include "TMCProcess.h"
49 #include "AliCollisionGeometry.h"
50 #include "AliGenCocktailEventHeader.h"
51 #include "AliGenCocktailEntry.h"
52 #include "AliGenCocktailAfterBurner.h"
53 #include "AliGenDeuteron.h"
56 ClassImp(AliGenDeuteron)
58 AliGenDeuteron::AliGenDeuteron(Int_t sign, Double_t pmax, Double_t rmax, Int_t cluster)
63 ,fClusterType(cluster)
75 fSign = sign > 0 ? 1:-1;
79 AliGenDeuteron::~AliGenDeuteron()
86 void AliGenDeuteron::Init()
89 // Standard AliGenerator initializer
93 void AliGenDeuteron::Generate()
96 // Look for coalescence of (anti)nucleons in the nucleon source
97 // provided by the generator cocktail
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));
102 AliGenCocktailAfterBurner* gener = (AliGenCocktailAfterBurner*)gAlice->GetMCApp()->Generator();
104 // find nuclear radius, only for first generator and projectile=target
105 Bool_t collisionGeometry=0;
106 if(fModel != kNone && gener->FirstGenerator()->Generator()->ProvidesCollisionGeometry())
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;
117 for(Int_t ns = 0; ns < gener->GetNumberOfEvents(); ++ns)
119 gener->SetActiveEventNumber(ns);
121 if(fModel != kNone && collisionGeometry)
123 fPsiR = (gener->GetCollisionGeometry(ns))->ReactionPlaneAngle();
124 fB = (gener->GetCollisionGeometry(ns))->ImpactParameter();
126 if(fB >= 2.*fR) continue; // no collision
129 fCurStack = gener->GetStack(ns);
132 AliWarning("no event stack");
136 TList* protons = new TList();
137 protons->SetOwner(kFALSE);
138 TList* neutrons = new TList();
139 neutrons->SetOwner(kFALSE);
141 // particles produced by the generator
142 for (Int_t i=0; i < fCurStack->GetNprimary(); ++i)
144 TParticle* iParticle = fCurStack->Particle(i);
146 if(iParticle->GetStatusCode() != 1) continue;
148 Int_t pdgCode = iParticle->GetPdgCode();
149 if(pdgCode == fSign*2212)// (anti)proton
151 FixProductionVertex(iParticle);
152 protons->Add(iParticle);
154 else if(pdgCode == fSign*2112) // (anti)neutron
156 FixProductionVertex(iParticle);
157 neutrons->Add(iParticle);
162 if(fClusterType==kFirstPartner)
164 FirstPartner(protons, neutrons);
168 WeightMatrix(protons, neutrons);
171 protons->Clear("nodelete");
172 neutrons->Clear("nodelete");
181 Double_t AliGenDeuteron::GetCoalescenceProbability(const TParticle* nucleon1, const TParticle* nucleon2) const
184 // Coalescence conditions as in
185 // A. J. Baltz et al., Phys. lett B 325(1994)7
187 // returns < 0 if coalescence is not possible
188 // otherwise returns a coalescence probability
190 const Double_t kProtonMass = 0.938272013;
191 const Double_t kNeutronMass = 0.939565378;
193 TVector3 v1(nucleon1->Vx(), nucleon1->Vy(), nucleon1->Vz());
194 TVector3 p1(nucleon1->Px(), nucleon1->Py(), nucleon1->Pz());
196 TVector3 v2(nucleon2->Vx(), nucleon2->Vy(), nucleon2->Vz());
197 TVector3 p2(nucleon2->Px(), nucleon2->Py(), nucleon2->Pz());
199 Double_t deltaP = 2.*this->GetPcm(p1, kProtonMass, p2, kNeutronMass); // relative momentum in CM frame
200 if( deltaP >= fPmax) return -1.;
202 Double_t deltaR = (v2-v1).Mag(); // relative distance (cm)
203 if(deltaR >= fRmax*1.e-13) return -1.;
205 if(Rndm() > fSpinProb) return -1.; // spin
207 if(fClusterType == kLowestMomentum) return 1. - deltaP/fPmax;
208 if(fClusterType == kLowestDistance) return 1. - 1.e+13*deltaR/fRmax;
210 return 1. - 1.e+13*(deltaP*deltaR)/(fRmax*fPmax);
213 void AliGenDeuteron::FirstPartner(const TList* protons, TList* neutrons)
216 // Clusters are made with the first nucleon pair that fulfill
217 // the coalescence conditions, starting with the protons
219 TIter p_next(protons);
220 while(TParticle* n0 = (TParticle*) p_next())
222 TParticle* partner = 0;
223 TIter n_next(neutrons);
224 while(TParticle* n1 = (TParticle*) n_next() )
226 if(GetCoalescenceProbability(n0, n1) < 0 ) continue; // with next neutron
231 if(partner == 0) continue; // with next proton
233 PushDeuteron(n0, partner);
235 // Remove from the list for the next iteration
236 neutrons->Remove(partner);
240 void AliGenDeuteron::WeightMatrix(const TList* protons, const TList* neutrons)
243 // Build all possible nucleon pairs with their own probability
244 // and select only those with the highest coalescence probability
246 Int_t nMaxPairs = protons->GetSize()*neutrons->GetSize();
248 TParticle** cProton = new TParticle*[nMaxPairs];
249 TParticle** cNeutron = new TParticle*[nMaxPairs];
250 Double_t* cWeight = new Double_t[nMaxPairs];
252 // build all pairs with probability > 0
254 TIter p_next(protons);
255 while(TParticle* n1 = (TParticle*) p_next())
257 TIter n_next(neutrons);
258 while(TParticle* n2 = (TParticle*) n_next() )
260 Double_t weight = this->GetCoalescenceProbability(n1,n2);
261 if(weight < 0) continue;
265 cWeight[cIdx] = weight;
271 Int_t nPairs = cIdx + 1;
273 // find the interacting pairs:
274 // remove repeated pairs and select only
275 // the pair with the highest coalescence probability
277 Int_t nMaxIntPair = TMath::Min(protons->GetSize(), neutrons->GetSize());
279 TParticle** iProton = new TParticle*[nMaxIntPair];
280 TParticle** iNeutron = new TParticle*[nMaxIntPair];
281 Double_t* iWeight = new Double_t[nMaxIntPair];
288 for(Int_t i=0; i < nPairs; ++i)
290 if(cWeight[i] > wMax)
297 if(j == -1 ) break; // end
299 // Save the interacting pair
301 iProton[iIdx] = cProton[j];
302 iNeutron[iIdx] = cNeutron[j];
303 iWeight[iIdx] = cWeight[j];
305 // invalidate all combinations with these pairs for the next iteration
306 for(Int_t i=0; i < nPairs; ++i)
308 if(cProton[i] == iProton[iIdx]) cWeight[i] = -1.;
309 if(cNeutron[i] == iNeutron[iIdx]) cWeight[i] = -1.;
313 Int_t nIntPairs = iIdx + 1;
319 // Add the (anti)deuterons to the current event stack
320 for(Int_t i=0; i<nIntPairs; ++i)
322 TParticle* n1 = iProton[i];
323 TParticle* n2 = iNeutron[i];
332 void AliGenDeuteron::PushDeuteron(TParticle* parent1, TParticle* parent2)
335 // Create an (anti)deuteron from parent1 and parent2,
336 // add to the current stack and set kDoneBit for the parents
338 const Double_t kDeuteronMass = 1.87561282;
339 const Int_t kDeuteronPdg = 1000010020;
342 TVector3 p1(parent1->Px(), parent1->Py(), parent1->Pz());
343 TVector3 p2(parent2->Px(), parent2->Py(), parent2->Pz());
346 // production vertex same as the parent1's
347 TVector3 vN(parent1->Vx(), parent1->Vy(), parent1->Vz());
350 Double_t energy = TMath::Sqrt(pN.Mag2() + kDeuteronMass*kDeuteronMass);
352 // Add a new (anti)deuteron to current event stack
353 fCurStack->PushTrack(1, -1, fSign*kDeuteronPdg,
354 pN.X(), pN.Y(), pN.Z(), energy,
355 vN.X(), vN.Y(), vN.Z(), parent1->T(),
356 0., 0., 0., kPNCapture, fNtrk, 1., 0);
358 // Set kDoneBit for the parents
359 parent1->SetBit(kDoneBit);
360 parent2->SetBit(kDoneBit);
363 void AliGenDeuteron::FixProductionVertex(TParticle* i)
366 // Replace current generator nucleon spatial distribution
367 // with a custom distribution according to the selected model
369 if(fModel == kNone || fModel > kExpansion) return;
371 // semi-axis from collision geometry (fm)
372 Double_t a = fTimeLength + TMath::Sqrt(fR*fR - fB*fB/4.);
373 Double_t b = fTimeLength + fR - fB/2.;
374 Double_t c = fTimeLength;
380 if(fModel == kThermal)
382 // uniformly ditributed in the volume on an ellipsoid
383 // random (r,theta,phi) unit sphere
384 Double_t r = TMath::Power(Rndm(),1./3.);
385 Double_t theta = TMath::ACos(2.*Rndm()-1.);
386 Double_t phi = 2.*TMath::Pi()*Rndm();
388 // transform coordenates
389 xx = a*r*TMath::Sin(theta)*TMath::Cos(phi);
390 yy = b*r*TMath::Sin(theta)*TMath::Sin(phi);
391 zz = c*r*TMath::Cos(theta);
393 else if(fModel == kExpansion)
395 // project into the surface of an ellipsoid
396 xx = a*TMath::Sin(i->Theta())*TMath::Cos(i->Phi());
397 yy = b*TMath::Sin(i->Theta())*TMath::Sin(i->Phi());
398 zz = c*TMath::Cos(i->Theta());
401 // rotate by the reaction plane angle
402 Double_t x = xx*TMath::Cos(fPsiR)+yy*TMath::Sin(fPsiR);
403 Double_t y = -xx*TMath::Sin(fPsiR)+yy*TMath::Cos(fPsiR);
406 // translate by the production vertex (cm)
407 i->SetProductionVertex(i->Vx() + 1.e-13*x, i->Vy() + 1.e-13*y, i->Vz() + 1.e-13*z, i->T());
410 Double_t AliGenDeuteron::GetS(Double_t p1x, Double_t p1y, Double_t p1z, Double_t m1, Double_t p2x, Double_t p2y, Double_t p2z, Double_t m2) const
413 // square of the center of mass energy
415 Double_t E1 = TMath::Sqrt( p1x*p1x + p1y*p1y + p1z*p1z + m1*m1);
416 Double_t E2 = TMath::Sqrt( p2x*p2x + p2y*p2y + p2z*p2z + m2*m2);
418 return (E1+E2)*(E1+E2) - ((p1x+p2x)*(p1x+p2x) + (p1y+p2y)*(p1y+p2y) + (p1z+p2z)*(p1z+p2z));
421 Double_t AliGenDeuteron::GetPcm(Double_t p1x, Double_t p1y, Double_t p1z, Double_t m1, Double_t p2x, Double_t p2y, Double_t p2z, Double_t m2) const
424 // momentum in the CM frame
426 Double_t s = this->GetS(p1x, p1y, p1z, m1, p2x, p2y, p2z, m2);
428 return TMath::Sqrt( (s-(m1-m2)*(m1-m2))*(s-(m1+m2)*(m1+m2)) )/(2.*TMath::Sqrt(s));
431 Double_t AliGenDeuteron::GetPcm(const TVector3& p1, Double_t m1, const TVector3& p2, Double_t m2) const
434 // momentum in the CM frame
436 return this->GetPcm(p1.Px(),p1.Py(),p1.Pz(),m1,p2.Px(),p2.Py(),p2.Pz(),m2);