1 /**************************************************************************
2 * Copyright(c) 1998-1999, 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 **************************************************************************/
19 // Generator for slow nucleons in pA interactions.
20 // Source is modelled by a relativistic Maxwell distributions.
21 // This class cooparates with AliCollisionGeometry if used inside AliGenCocktail.
22 // In this case the number of slow nucleons is determined from the number of wounded nuclei
23 // using a realisation of AliSlowNucleonModel.
24 // Original code by Ferenc Sikler <sikler@rmki.kfki.hu>
27 #include <TDatabasePDG.h>
33 #include <TParticle.h>
36 #include "AliCollisionGeometry.h"
40 #include "AliGenSlowNucleons.h"
41 #include "AliSlowNucleonModel.h"
43 ClassImp(AliGenSlowNucleons)
46 AliGenSlowNucleons::AliGenSlowNucleons()
68 fBeamCrossingAngle(0.),
73 // Default constructor
74 fCollisionGeometry = 0;
77 AliGenSlowNucleons::AliGenSlowNucleons(Int_t npart)
99 fBeamCrossingAngle(0.),
102 fSlowNucleonModel(new AliSlowNucleonModel())
106 fName = "SlowNucleons";
107 fTitle = "Generator for gray particles in pA collisions";
108 fCollisionGeometry = 0;
111 //____________________________________________________________
112 AliGenSlowNucleons::~AliGenSlowNucleons()
115 delete fSlowNucleonModel;
118 void AliGenSlowNucleons::SetProtonDirection(Float_t dir) {
119 // Set direction of the proton to change between pA (1) and Ap (-1)
120 fProtonDirection = dir / TMath::Abs(dir);
123 void AliGenSlowNucleons::Init()
128 Double_t kMass = TDatabasePDG::Instance()->GetParticle(kProton)->Mass();
129 fMomentum = fCMS/2. * Float_t(fZTarget) / Float_t(fATarget);
130 fBeta = fMomentum / TMath::Sqrt(kMass * kMass + fMomentum * fMomentum);
131 //printf(" fMomentum %f fBeta %1.10f\n",fMomentum, fBeta);
133 fDebugHist1 = new TH2F("DebugHist1", "nu vs N_slow", 100, 0., 100., 20, 0., 20.);
134 fDebugHist2 = new TH2F("DebugHist2", "b vs N_slow", 100, 0., 100., 15, 0., 15.);
135 fCosThetaGrayHist = new TH1F("fCosThetaGrayHist", "Gray particles angle", 100, -1., 1.);
138 // non-uniform cos(theta) distribution
140 if(fThetaDistribution != 0) {
141 fCosTheta = new TF1("fCosTheta",
142 "(2./3.14159265358979312)/(exp(2./3.14159265358979312)-exp(-2./3.14159265358979312))*exp(2.*x/3.14159265358979312)",
146 printf("\n AliGenSlowNucleons: applying crossing angle %f mrad to slow nucleons\n",fBeamCrossingAngle*1000.);
149 void AliGenSlowNucleons::FinishRun()
152 // Show histogram for debugging if requested.
154 TCanvas *c = new TCanvas("c","Canvas 1",400,10,600,700);
157 fDebugHist1->Draw("colz");
161 fCosThetaGrayHist->Draw();
166 void AliGenSlowNucleons::Generate()
169 // Generate one event
172 // Communication with Gray Particle Model
174 if (fCollisionGeometry) {
175 Float_t b = fCollisionGeometry->ImpactParameter();
176 // Int_t nn = fCollisionGeometry->NN();
177 // Int_t nwn = fCollisionGeometry->NwN();
178 // Int_t nnw = fCollisionGeometry->NNw();
179 // Int_t nwnw = fCollisionGeometry->NwNw();
181 //fSlowNucleonModel->GetNumberOfSlowNucleons(fCollisionGeometry, fNgp, fNgn, fNbp, fNbn);
182 fSlowNucleonModel->GetNumberOfSlowNucleons2(fCollisionGeometry, fNgp, fNgn, fNbp, fNbn);
184 //printf("Collision Geometry %f %d %d %d %d\n", b, nn, nwn, nnw, nwnw);
185 printf("Slow nucleons: %d grayp %d grayn %d blackp %d blackn \n", fNgp, fNgn, fNbp, fNbn);
186 fDebugHist1->Fill(Float_t(fNgp + fNgn + fNbp + fNbn), fCollisionGeometry->NNw(), 1.);
187 fDebugHist2->Fill(Float_t(fNgp + fNgn + fNbp + fNbn), b, 1.);
193 Float_t p[3] = {0., 0., 0.}, theta=0;
194 Float_t origin[3] = {0., 0., 0.};
196 Float_t polar [3] = {0., 0., 0.};
200 // Extracting 1 value per event for the divergence angle
201 Double_t rvec = gRandom->Gaus(0.0, 1.0);
202 fBeamDivEvent = fBeamDivergence * TMath::Abs(rvec);
203 printf("\n AliGenSlowNucleons: applying beam divergence %f mrad to slow nucleons\n",fBeamDivEvent*1000.);
205 if(fVertexSmear == kPerEvent) {
207 for (j=0; j < 3; j++) origin[j] = fVertex[j];
215 for(i = 0; i < fNgp; i++) {
216 GenerateSlow(fCharge, fTemperatureG, fBetaSourceG, p, theta);
217 if (fDebug) fCosThetaGrayHist->Fill(TMath::Cos(theta));
218 PushTrack(fTrackIt, -1, kf, p, origin, polar,
219 time, kPNoProcess, nt, 1.,-2);
221 SetProcessID(nt,kGrayProcess);
228 for(i = 0; i < fNgn; i++) {
229 GenerateSlow(fCharge, fTemperatureG, fBetaSourceG, p, theta);
230 if (fDebug) fCosThetaGrayHist->Fill(TMath::Cos(theta));
231 PushTrack(fTrackIt, -1, kf, p, origin, polar,
232 time, kPNoProcess, nt, 1.,-2);
234 SetProcessID(nt,kGrayProcess);
241 for(i = 0; i < fNbp; i++) {
242 GenerateSlow(fCharge, fTemperatureB, fBetaSourceB, p, theta);
243 PushTrack(fTrackIt, -1, kf, p, origin, polar,
244 time, kPNoProcess, nt, 1.,-1);
246 SetProcessID(nt,kBlackProcess);
253 for(i = 0; i < fNbn; i++) {
254 GenerateSlow(fCharge, fTemperatureB, fBetaSourceB, p, theta);
255 PushTrack(fTrackIt, -1, kf, p, origin, polar,
256 time, kPNoProcess, nt, 1.,-1);
258 SetProcessID(nt,kBlackProcess);
265 void AliGenSlowNucleons::GenerateSlow(Int_t charge, Double_t T,
266 Double_t beta, Float_t* q, Float_t &theta)
270 Emit a slow nucleon with "temperature" T [GeV],
271 from a source moving with velocity beta
272 Three-momentum [GeV/c] is given back in q[3]
275 //printf("Generating slow nuc. with: charge %d. temp. %1.4f, beta %f \n",charge,T,beta);
277 Double_t m, pmax, p, f, phi;
278 TDatabasePDG * pdg = TDatabasePDG::Instance();
279 const Double_t kMassProton = pdg->GetParticle(kProton) ->Mass();
280 const Double_t kMassNeutron = pdg->GetParticle(kNeutron)->Mass();
282 /* Select nucleon type */
283 if(charge == 0) m = kMassNeutron;
284 else m = kMassProton;
286 /* Momentum at maximum of Maxwell-distribution */
288 pmax = TMath::Sqrt(2*T*(T+TMath::Sqrt(T*T+m*m)));
290 /* Try until proper momentum */
291 /* for lack of primitive function of the Maxwell-distribution */
292 /* a brute force trial-accept loop, normalized at pmax */
297 f = Maxwell(m, p, T) / Maxwell(m , pmax, T);
301 /* Spherical symmetric emission for black particles (beta=0)*/
302 if(beta==0 || fThetaDistribution==0) theta = TMath::ACos(2. * Rndm() - 1.);
303 /* cos theta distributed according to experimental results for gray particles (beta=0.05)*/
304 else if(fThetaDistribution!=0){
305 Double_t costheta = fCosTheta->GetRandom();
306 theta = TMath::ACos(costheta);
309 phi = 2. * TMath::Pi() * Rndm();
312 /* Determine momentum components in system of the moving source */
313 q[0] = p * TMath::Sin(theta) * TMath::Cos(phi);
314 q[1] = p * TMath::Sin(theta) * TMath::Sin(phi);
315 q[2] = p * TMath::Cos(theta);
316 //if(fDebug==1) printf("\n Momentum in RS of the moving source: p = (%f, %f, %f)\n",q[0],q[1],q[2]);
319 /* Transform to system of the target nucleus */
320 /* beta is passed as negative, because the gray nucleons are slowed down */
321 Lorentz(m, -beta, q);
322 //if(fDebug==1) printf(" Momentum in RS of the target nucleus: p = (%f, %f, %f)\n",q[0],q[1],q[2]);
324 /* Transform to laboratory system */
325 Lorentz(m, fBeta, q);
326 q[2] *= fProtonDirection;
327 if(fDebug==1)printf("\n Momentum after LHC boost: p = (%f, %f, %f)\n",q[0],q[1],q[2]);
329 if(fBeamCrossingAngle>0.) BeamCrossDivergence(1, q); // applying crossing angle
330 if(fBeamDivergence>0.) BeamCrossDivergence(2, q); // applying divergence
334 Double_t AliGenSlowNucleons::Maxwell(Double_t m, Double_t p, Double_t T)
336 /* Relativistic Maxwell-distribution */
338 ekin = TMath::Sqrt(p*p+m*m)-m;
339 return (p*p * exp(-ekin/T));
343 //_____________________________________________________________________________
344 void AliGenSlowNucleons::Lorentz(Double_t m, Double_t beta, Float_t* q)
346 /* Lorentz transform in the direction of q[2] */
348 Double_t gamma = 1./TMath::Sqrt((1.-beta)*(1.+beta));
349 Double_t energy = TMath::Sqrt(m*m + q[0]*q[0] + q[1]*q[1] + q[2]*q[2]);
350 q[2] = gamma * (q[2] + beta*energy);
351 //printf(" \t beta %1.10f gamma %f energy %f -> p_z = %f\n",beta, gamma, energy,q[2]);
354 //_____________________________________________________________________________
355 void AliGenSlowNucleons::BeamCrossDivergence(Int_t iwhat, Float_t *pLab)
357 // Applying beam divergence and crossing angle
359 Double_t pmod = TMath::Sqrt(pLab[0]*pLab[0]+pLab[1]*pLab[1]+pLab[2]*pLab[2]);
361 Double_t tetdiv = 0.;
364 tetdiv = fBeamCrossingAngle;
368 tetdiv = fBeamDivEvent;
369 fidiv = (gRandom->Rndm())*k2PI;
372 Double_t tetpart = TMath::ATan2(TMath::Sqrt(pLab[0]*pLab[0]+pLab[1]*pLab[1]), pLab[2]);
374 if(TMath::Abs(pLab[1])>0. || TMath::Abs(pLab[0])>0.) fipart = TMath::ATan2(pLab[1], pLab[0]);
375 if(fipart<0.) {fipart = fipart+k2PI;}
376 tetdiv = tetdiv*kRaddeg;
377 fidiv = fidiv*kRaddeg;
378 tetpart = tetpart*kRaddeg;
379 fipart = fipart*kRaddeg;
381 Double_t angleSum[2]={0., 0.};
382 AddAngle(tetpart,fipart,tetdiv,fidiv,angleSum);
384 Double_t tetsum = angleSum[0];
385 Double_t fisum = angleSum[1];
386 //printf("tetpart %f fipart %f tetdiv %f fidiv %f angleSum %f %f\n",tetpart,fipart,tetdiv,fidiv,angleSum[0],angleSum[1]);
387 tetsum = tetsum*kDegrad;
388 fisum = fisum*kDegrad;
390 pLab[0] = pmod*TMath::Sin(tetsum)*TMath::Cos(fisum);
391 pLab[1] = pmod*TMath::Sin(tetsum)*TMath::Sin(fisum);
392 pLab[2] = pmod*TMath::Cos(tetsum);
394 if(iwhat==1) printf(" Beam crossing angle %f mrad ", fBeamCrossingAngle*1000.);
395 else if(iwhat==2) printf(" Beam divergence %f mrad ", fBeamDivEvent*1000.);
396 printf(" p = (%f, %f, %f)\n",pLab[0],pLab[1],pLab[2]);
400 //_____________________________________________________________________________
401 void AliGenSlowNucleons::AddAngle(Double_t theta1, Double_t phi1,
402 Double_t theta2, Double_t phi2, Double_t *angleSum)
404 // Calculating the sum of 2 angles
406 Double_t conv = 180./TMath::ACos(temp);
408 Double_t ct1 = TMath::Cos(theta1/conv);
409 Double_t st1 = TMath::Sin(theta1/conv);
410 Double_t cp1 = TMath::Cos(phi1/conv);
411 Double_t sp1 = TMath::Sin(phi1/conv);
412 Double_t ct2 = TMath::Cos(theta2/conv);
413 Double_t st2 = TMath::Sin(theta2/conv);
414 Double_t cp2 = TMath::Cos(phi2/conv);
415 Double_t sp2 = TMath::Sin(phi2/conv);
416 Double_t cx = ct1*cp1*st2*cp2+st1*cp1*ct2-sp1*st2*sp2;
417 Double_t cy = ct1*sp1*st2*cp2+st1*sp1*ct2+cp1*st2*sp2;
418 Double_t cz = ct1*ct2-st1*st2*cp2;
420 Double_t rtetsum = TMath::ACos(cz);
421 Double_t tetsum = conv*rtetsum;
422 if(TMath::Abs(tetsum)<1e-4 || tetsum==180.) return;
424 temp = cx/TMath::Sin(rtetsum);
426 if(temp<-1.) temp=-1.;
427 Double_t fisum = conv*TMath::ACos(temp);
428 if(cy<0) {fisum = 360.-fisum;}
430 angleSum[0] = tetsum;
434 //_____________________________________________________________________________
435 void AliGenSlowNucleons::SetProcessID(Int_t nt, UInt_t process)
437 // Tag the particle as
440 fStack->Particle(nt)->SetUniqueID(process);
442 gAlice->GetMCApp()->Particle(nt)->SetUniqueID(process);