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c9a8628a | 1 | /************************************************************************** |
2 | * Copyright(c) 1998-1999, ALICE Experiment at CERN, All rights reserved. * | |
3 | * * | |
4 | * Author: The ALICE Off-line Project. * | |
5 | * Contributors are mentioned in the code where appropriate. * | |
6 | * * | |
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 | **************************************************************************/ | |
15 | ||
88cb7938 | 16 | /* $Id$ */ |
c9a8628a | 17 | |
f687abfe | 18 | // |
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> | |
25 | // | |
c9a8628a | 26 | |
27 | #include <TDatabasePDG.h> | |
28 | #include <TPDGCode.h> | |
29 | #include <TH2F.h> | |
c8f7f6f9 | 30 | #include <TCanvas.h> |
c9a8628a | 31 | |
32 | #include "AliCollisionGeometry.h" | |
33 | #include "AliGenSlowNucleons.h" | |
34 | #include "AliSlowNucleonModel.h" | |
35 | ||
36 | ClassImp(AliGenSlowNucleons) | |
37 | ||
38 | AliGenSlowNucleons::AliGenSlowNucleons():AliGenerator(-1) | |
39 | { | |
40 | // Default constructor | |
41 | fSlowNucleonModel = 0; | |
42 | fCollisionGeometry = 0; | |
43 | } | |
44 | ||
45 | AliGenSlowNucleons::AliGenSlowNucleons(Int_t npart) | |
46 | :AliGenerator(npart) | |
47 | { | |
48 | // Constructor | |
49 | fName = "SlowNucleons"; | |
50 | fTitle = "Generator for gray particles in pA collisions"; | |
51 | SetPmax(); | |
52 | SetTarget(); | |
53 | SetNominalCmsEnergy(); | |
54 | SetCharge(); | |
55 | SetTemperature(); | |
56 | SetBetaSource(); | |
57 | fSlowNucleonModel = new AliSlowNucleonModel(); | |
58 | fCollisionGeometry = 0; | |
59 | fDebug = 0; | |
60 | } | |
61 | ||
f687abfe | 62 | AliGenSlowNucleons::AliGenSlowNucleons(const AliGenSlowNucleons & sn): |
63 | AliGenerator(sn) | |
64 | { | |
65 | // Copy constructor | |
66 | sn.Copy(*this); | |
67 | } | |
68 | ||
c9a8628a | 69 | //____________________________________________________________ |
70 | AliGenSlowNucleons::~AliGenSlowNucleons() | |
71 | { | |
72 | // Destructor | |
73 | delete fSlowNucleonModel; | |
74 | } | |
75 | ||
83b3cd6c | 76 | void AliGenSlowNucleons::SetProtonDirection(Float_t dir) { |
77 | // Set direction of the proton to change between pA (1) and Ap (-1) | |
78 | fProtonDirection = dir / TMath::Abs(dir); | |
79 | } | |
c9a8628a | 80 | |
81 | void AliGenSlowNucleons::Init() | |
82 | { | |
83 | // | |
84 | // Initialization | |
85 | // | |
86 | Float_t kMass = TDatabasePDG::Instance()->GetParticle(kProton)->Mass(); | |
87 | fMomentum = fCMS/2. * fZTarget / fATarget; | |
88 | fBeta = fMomentum / TMath::Sqrt(kMass * kMass + fMomentum * fMomentum); | |
89 | if (fDebug) { | |
c8f7f6f9 | 90 | fDebugHist1 = new TH2F("DebugHist1", "nu vs N_slow", 100, 0., 100., 20, 0., 20.); |
91 | fDebugHist2 = new TH2F("DebugHist2", "b vs N_slow", 100, 0., 100., 15, 0., 15.); | |
c9a8628a | 92 | } |
93 | } | |
94 | ||
95 | void AliGenSlowNucleons::FinishRun() | |
96 | { | |
f687abfe | 97 | // End of run action |
98 | // Show histogram for debugging if requested. | |
c9a8628a | 99 | if (fDebug) { |
c8f7f6f9 | 100 | TCanvas *c = new TCanvas("c","Canvas 1",400,10,600,700); |
101 | c->Divide(2,1); | |
102 | c->cd(1); | |
103 | fDebugHist1->Draw(); | |
104 | c->cd(2); | |
105 | fDebugHist2->Draw(); | |
c9a8628a | 106 | } |
107 | } | |
108 | ||
109 | ||
110 | void AliGenSlowNucleons::Generate() | |
111 | { | |
112 | // | |
113 | // Generate one event | |
114 | // | |
115 | // | |
116 | // Communication with Gray Particle Model | |
117 | // | |
1c22a81e | 118 | if (fCollisionGeometry) { |
119 | Float_t b = fCollisionGeometry->ImpactParameter(); | |
120 | Int_t nn = fCollisionGeometry->NN(); | |
121 | Int_t nwn = fCollisionGeometry->NwN(); | |
122 | Int_t nnw = fCollisionGeometry->NNw(); | |
123 | Int_t nwnw = fCollisionGeometry->NwNw(); | |
124 | ||
99f5114f | 125 | fSlowNucleonModel->GetNumberOfSlowNucleons(fCollisionGeometry, fNgp, fNgn, fNbp, fNbn); |
1c22a81e | 126 | if (fDebug) { |
127 | printf("Nucleons %d %d %d %d \n", fNgp, fNgn, fNbp, fNbn); | |
c8f7f6f9 | 128 | fDebugHist1->Fill(Float_t(fNgp + fNgn + fNbp + fNbn), fCollisionGeometry->NwN(), 1.); |
129 | fDebugHist2->Fill(Float_t(fNgp + fNgn + fNbp + fNbn), b, 1.); | |
1c22a81e | 130 | printf("AliGenSlowNucleons: Impact parameter from Collision Geometry %f %d %d %d %d\n", |
131 | b, nn, nwn, nnw, nwnw); | |
132 | } | |
133 | } | |
c9a8628a | 134 | |
135 | // | |
136 | Float_t p[3]; | |
137 | Float_t origin[3] = {0., 0., 0.}; | |
138 | Float_t polar [3] = {0., 0., 0.}; | |
99f5114f | 139 | Int_t nt, i, j; |
c9a8628a | 140 | Int_t kf; |
99f5114f | 141 | |
142 | if(fVertexSmear == kPerEvent) { | |
143 | Vertex(); | |
144 | for (j=0; j < 3; j++) origin[j] = fVertex[j]; | |
145 | } // if kPerEvent | |
c9a8628a | 146 | // |
147 | // Gray protons | |
148 | // | |
149 | fCharge = 1; | |
150 | kf = kProton; | |
1c22a81e | 151 | for(i = 0; i < fNgp; i++) { |
c9a8628a | 152 | GenerateSlow(fCharge, fTemperatureG, fBetaSourceG, p); |
642f15cf | 153 | PushTrack(fTrackIt, -1, kf, p, origin, polar, |
c9a8628a | 154 | 0., kPNoProcess, nt, 1.); |
155 | KeepTrack(nt); | |
156 | } | |
157 | // | |
158 | // Gray neutrons | |
159 | // | |
160 | fCharge = 0; | |
161 | kf = kNeutron; | |
1c22a81e | 162 | for(i = 0; i < fNgn; i++) { |
c9a8628a | 163 | GenerateSlow(fCharge, fTemperatureG, fBetaSourceG, p); |
642f15cf | 164 | PushTrack(fTrackIt, -1, kf, p, origin, polar, |
c9a8628a | 165 | 0., kPNoProcess, nt, 1.); |
166 | KeepTrack(nt); | |
167 | } | |
168 | // | |
169 | // Black protons | |
170 | // | |
171 | fCharge = 1; | |
172 | kf = kProton; | |
1c22a81e | 173 | for(i = 0; i < fNbp; i++) { |
c9a8628a | 174 | GenerateSlow(fCharge, fTemperatureB, fBetaSourceB, p); |
642f15cf | 175 | PushTrack(fTrackIt, -1, kf, p, origin, polar, |
c9a8628a | 176 | 0., kPNoProcess, nt, 1.); |
177 | KeepTrack(nt); | |
178 | } | |
179 | // | |
180 | // Black neutrons | |
181 | // | |
182 | fCharge = 0; | |
183 | kf = kNeutron; | |
1c22a81e | 184 | for(i = 0; i < fNbn; i++) { |
c9a8628a | 185 | GenerateSlow(fCharge, fTemperatureB, fBetaSourceB, p); |
642f15cf | 186 | PushTrack(fTrackIt, -1, kf, p, origin, polar, |
c9a8628a | 187 | 0., kPNoProcess, nt, 1.); |
188 | KeepTrack(nt); | |
189 | } | |
190 | } | |
191 | ||
192 | ||
193 | ||
194 | ||
195 | void AliGenSlowNucleons::GenerateSlow(Int_t charge, Double_t T, Double_t beta, Float_t* q) | |
f687abfe | 196 | |
197 | { | |
c9a8628a | 198 | /* |
199 | Emit a slow nucleon with "temperature" T [GeV], | |
200 | from a source moving with velocity beta | |
201 | Three-momentum [GeV/c] is given back in q[3] | |
202 | */ | |
203 | ||
c9a8628a | 204 | Double_t m, pmax, p, f, theta, phi; |
c9a8628a | 205 | TDatabasePDG * pdg = TDatabasePDG::Instance(); |
206 | const Double_t kMassProton = pdg->GetParticle(kProton) ->Mass(); | |
207 | const Double_t kMassNeutron = pdg->GetParticle(kNeutron)->Mass(); | |
208 | ||
209 | /* Select nucleon type */ | |
210 | if(charge == 0) m = kMassNeutron; | |
211 | else m = kMassProton; | |
212 | ||
213 | /* Momentum at maximum of Maxwell-distribution */ | |
214 | ||
215 | pmax = TMath::Sqrt(2*T*(T+sqrt(T*T+m*m))); | |
216 | ||
217 | /* Try until proper momentum */ | |
218 | /* for lack of primitive function of the Maxwell-distribution */ | |
219 | /* a brute force trial-accept loop, normalized at pmax */ | |
220 | ||
221 | do | |
222 | { | |
223 | p = Rndm() * fPmax; | |
224 | f = Maxwell(m, p, T) / Maxwell(m , pmax, T); | |
225 | } | |
226 | while(f < Rndm()); | |
227 | ||
228 | /* Spherical symmetric emission */ | |
229 | theta = TMath::ACos(2. * Rndm() - 1.); | |
230 | phi = 2. * TMath::Pi() * Rndm(); | |
231 | ||
232 | /* Determine momentum components in system of the moving source */ | |
233 | q[0] = p * TMath::Sin(theta) * TMath::Cos(phi); | |
234 | q[1] = p * TMath::Sin(theta) * TMath::Sin(phi); | |
235 | q[2] = p * TMath::Cos(theta); | |
236 | ||
237 | /* Transform to system of the target nucleus */ | |
238 | /* beta is passed as negative, because the gray nucleons are slowed down */ | |
239 | Lorentz(m, -beta, q); | |
240 | ||
241 | /* Transform to laboratory system */ | |
242 | Lorentz(m, fBeta, q); | |
83b3cd6c | 243 | q[2] *= fProtonDirection; |
c9a8628a | 244 | } |
245 | ||
246 | Double_t AliGenSlowNucleons::Maxwell(Double_t m, Double_t p, Double_t T) | |
247 | { | |
248 | /* Relativistic Maxwell-distribution */ | |
249 | Double_t ekin; | |
250 | ekin = TMath::Sqrt(p*p+m*m)-m; | |
251 | return (p*p * exp(-ekin/T)); | |
252 | } | |
253 | ||
254 | ||
255 | void AliGenSlowNucleons::Lorentz(Double_t m, Double_t beta, Float_t* q) | |
256 | { | |
257 | /* Lorentz transform in the direction of q[2] */ | |
258 | ||
259 | Double_t gamma = 1/sqrt(1-beta*beta); | |
260 | Double_t energy = sqrt(m*m + q[0]*q[0] + q[1]*q[1] + q[2]*q[2]); | |
261 | q[2] = gamma * (q[2] + beta*energy); | |
262 | } | |
263 | ||
f687abfe | 264 | |
265 | AliGenSlowNucleons& AliGenSlowNucleons::operator=(const AliGenSlowNucleons& rhs) | |
266 | { | |
267 | // Assignment operator | |
268 | rhs.Copy(*this); | |
269 | return *this; | |
270 | } | |
271 | ||
dc1d768c | 272 | void AliGenSlowNucleons::Copy(TObject&) const |
f687abfe | 273 | { |
274 | // | |
275 | // Copy | |
276 | // | |
277 | Fatal("Copy","Not implemented!\n"); | |
278 | } | |
279 | ||
c9a8628a | 280 | |
281 | ||
282 | ||
283 | ||
284 | ||
285 |