]>
Commit | Line | Data |
---|---|---|
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 | |
18 | /* | |
19 | Generator for slow nucluons in pA interactions. | |
20 | Source is modelled by a relativistic Maxwell distributions. | |
21 | Original code by Ferenc Sikler <sikler@rmki.kfki.hu> | |
22 | */ | |
23 | ||
24 | #include <TDatabasePDG.h> | |
25 | #include <TPDGCode.h> | |
26 | #include <TH2F.h> | |
c8f7f6f9 | 27 | #include <TCanvas.h> |
c9a8628a | 28 | |
29 | #include "AliCollisionGeometry.h" | |
30 | #include "AliGenSlowNucleons.h" | |
31 | #include "AliSlowNucleonModel.h" | |
32 | ||
33 | ClassImp(AliGenSlowNucleons) | |
34 | ||
35 | AliGenSlowNucleons::AliGenSlowNucleons():AliGenerator(-1) | |
36 | { | |
37 | // Default constructor | |
38 | fSlowNucleonModel = 0; | |
39 | fCollisionGeometry = 0; | |
40 | } | |
41 | ||
42 | AliGenSlowNucleons::AliGenSlowNucleons(Int_t npart) | |
43 | :AliGenerator(npart) | |
44 | { | |
45 | // Constructor | |
46 | fName = "SlowNucleons"; | |
47 | fTitle = "Generator for gray particles in pA collisions"; | |
48 | SetPmax(); | |
49 | SetTarget(); | |
50 | SetNominalCmsEnergy(); | |
51 | SetCharge(); | |
52 | SetTemperature(); | |
53 | SetBetaSource(); | |
54 | fSlowNucleonModel = new AliSlowNucleonModel(); | |
55 | fCollisionGeometry = 0; | |
56 | fDebug = 0; | |
57 | } | |
58 | ||
59 | //____________________________________________________________ | |
60 | AliGenSlowNucleons::~AliGenSlowNucleons() | |
61 | { | |
62 | // Destructor | |
63 | delete fSlowNucleonModel; | |
64 | } | |
65 | ||
66 | ||
67 | void AliGenSlowNucleons::Init() | |
68 | { | |
69 | // | |
70 | // Initialization | |
71 | // | |
72 | Float_t kMass = TDatabasePDG::Instance()->GetParticle(kProton)->Mass(); | |
73 | fMomentum = fCMS/2. * fZTarget / fATarget; | |
74 | fBeta = fMomentum / TMath::Sqrt(kMass * kMass + fMomentum * fMomentum); | |
75 | if (fDebug) { | |
c8f7f6f9 | 76 | fDebugHist1 = new TH2F("DebugHist1", "nu vs N_slow", 100, 0., 100., 20, 0., 20.); |
77 | fDebugHist2 = new TH2F("DebugHist2", "b vs N_slow", 100, 0., 100., 15, 0., 15.); | |
c9a8628a | 78 | } |
79 | } | |
80 | ||
81 | void AliGenSlowNucleons::FinishRun() | |
82 | { | |
83 | if (fDebug) { | |
c8f7f6f9 | 84 | TCanvas *c = new TCanvas("c","Canvas 1",400,10,600,700); |
85 | c->Divide(2,1); | |
86 | c->cd(1); | |
87 | fDebugHist1->Draw(); | |
88 | c->cd(2); | |
89 | fDebugHist2->Draw(); | |
c9a8628a | 90 | } |
91 | } | |
92 | ||
93 | ||
94 | void AliGenSlowNucleons::Generate() | |
95 | { | |
96 | // | |
97 | // Generate one event | |
98 | // | |
99 | // | |
100 | // Communication with Gray Particle Model | |
101 | // | |
1c22a81e | 102 | if (fCollisionGeometry) { |
103 | Float_t b = fCollisionGeometry->ImpactParameter(); | |
104 | Int_t nn = fCollisionGeometry->NN(); | |
105 | Int_t nwn = fCollisionGeometry->NwN(); | |
106 | Int_t nnw = fCollisionGeometry->NNw(); | |
107 | Int_t nwnw = fCollisionGeometry->NwNw(); | |
108 | ||
99f5114f | 109 | fSlowNucleonModel->GetNumberOfSlowNucleons(fCollisionGeometry, fNgp, fNgn, fNbp, fNbn); |
1c22a81e | 110 | if (fDebug) { |
111 | printf("Nucleons %d %d %d %d \n", fNgp, fNgn, fNbp, fNbn); | |
c8f7f6f9 | 112 | fDebugHist1->Fill(Float_t(fNgp + fNgn + fNbp + fNbn), fCollisionGeometry->NwN(), 1.); |
113 | fDebugHist2->Fill(Float_t(fNgp + fNgn + fNbp + fNbn), b, 1.); | |
1c22a81e | 114 | printf("AliGenSlowNucleons: Impact parameter from Collision Geometry %f %d %d %d %d\n", |
115 | b, nn, nwn, nnw, nwnw); | |
116 | } | |
117 | } | |
c9a8628a | 118 | |
119 | // | |
120 | Float_t p[3]; | |
121 | Float_t origin[3] = {0., 0., 0.}; | |
122 | Float_t polar [3] = {0., 0., 0.}; | |
99f5114f | 123 | Int_t nt, i, j; |
c9a8628a | 124 | Int_t kf; |
99f5114f | 125 | |
126 | if(fVertexSmear == kPerEvent) { | |
127 | Vertex(); | |
128 | for (j=0; j < 3; j++) origin[j] = fVertex[j]; | |
129 | } // if kPerEvent | |
c9a8628a | 130 | // |
131 | // Gray protons | |
132 | // | |
133 | fCharge = 1; | |
134 | kf = kProton; | |
1c22a81e | 135 | for(i = 0; i < fNgp; i++) { |
c9a8628a | 136 | GenerateSlow(fCharge, fTemperatureG, fBetaSourceG, p); |
137 | SetTrack(fTrackIt, -1, kf, p, origin, polar, | |
138 | 0., kPNoProcess, nt, 1.); | |
139 | KeepTrack(nt); | |
140 | } | |
141 | // | |
142 | // Gray neutrons | |
143 | // | |
144 | fCharge = 0; | |
145 | kf = kNeutron; | |
1c22a81e | 146 | for(i = 0; i < fNgn; i++) { |
c9a8628a | 147 | GenerateSlow(fCharge, fTemperatureG, fBetaSourceG, p); |
148 | SetTrack(fTrackIt, -1, kf, p, origin, polar, | |
149 | 0., kPNoProcess, nt, 1.); | |
150 | KeepTrack(nt); | |
151 | } | |
152 | // | |
153 | // Black protons | |
154 | // | |
155 | fCharge = 1; | |
156 | kf = kProton; | |
1c22a81e | 157 | for(i = 0; i < fNbp; i++) { |
c9a8628a | 158 | GenerateSlow(fCharge, fTemperatureB, fBetaSourceB, p); |
159 | SetTrack(fTrackIt, -1, kf, p, origin, polar, | |
160 | 0., kPNoProcess, nt, 1.); | |
161 | KeepTrack(nt); | |
162 | } | |
163 | // | |
164 | // Black neutrons | |
165 | // | |
166 | fCharge = 0; | |
167 | kf = kNeutron; | |
1c22a81e | 168 | for(i = 0; i < fNbn; i++) { |
c9a8628a | 169 | GenerateSlow(fCharge, fTemperatureB, fBetaSourceB, p); |
170 | SetTrack(fTrackIt, -1, kf, p, origin, polar, | |
171 | 0., kPNoProcess, nt, 1.); | |
172 | KeepTrack(nt); | |
173 | } | |
174 | } | |
175 | ||
176 | ||
177 | ||
178 | ||
179 | void AliGenSlowNucleons::GenerateSlow(Int_t charge, Double_t T, Double_t beta, Float_t* q) | |
180 | /* | |
181 | Emit a slow nucleon with "temperature" T [GeV], | |
182 | from a source moving with velocity beta | |
183 | Three-momentum [GeV/c] is given back in q[3] | |
184 | */ | |
185 | ||
186 | { | |
187 | Double_t m, pmax, p, f, theta, phi; | |
188 | ||
189 | TDatabasePDG * pdg = TDatabasePDG::Instance(); | |
190 | const Double_t kMassProton = pdg->GetParticle(kProton) ->Mass(); | |
191 | const Double_t kMassNeutron = pdg->GetParticle(kNeutron)->Mass(); | |
192 | ||
193 | /* Select nucleon type */ | |
194 | if(charge == 0) m = kMassNeutron; | |
195 | else m = kMassProton; | |
196 | ||
197 | /* Momentum at maximum of Maxwell-distribution */ | |
198 | ||
199 | pmax = TMath::Sqrt(2*T*(T+sqrt(T*T+m*m))); | |
200 | ||
201 | /* Try until proper momentum */ | |
202 | /* for lack of primitive function of the Maxwell-distribution */ | |
203 | /* a brute force trial-accept loop, normalized at pmax */ | |
204 | ||
205 | do | |
206 | { | |
207 | p = Rndm() * fPmax; | |
208 | f = Maxwell(m, p, T) / Maxwell(m , pmax, T); | |
209 | } | |
210 | while(f < Rndm()); | |
211 | ||
212 | /* Spherical symmetric emission */ | |
213 | theta = TMath::ACos(2. * Rndm() - 1.); | |
214 | phi = 2. * TMath::Pi() * Rndm(); | |
215 | ||
216 | /* Determine momentum components in system of the moving source */ | |
217 | q[0] = p * TMath::Sin(theta) * TMath::Cos(phi); | |
218 | q[1] = p * TMath::Sin(theta) * TMath::Sin(phi); | |
219 | q[2] = p * TMath::Cos(theta); | |
220 | ||
221 | /* Transform to system of the target nucleus */ | |
222 | /* beta is passed as negative, because the gray nucleons are slowed down */ | |
223 | Lorentz(m, -beta, q); | |
224 | ||
225 | /* Transform to laboratory system */ | |
226 | Lorentz(m, fBeta, q); | |
227 | } | |
228 | ||
229 | Double_t AliGenSlowNucleons::Maxwell(Double_t m, Double_t p, Double_t T) | |
230 | { | |
231 | /* Relativistic Maxwell-distribution */ | |
232 | Double_t ekin; | |
233 | ekin = TMath::Sqrt(p*p+m*m)-m; | |
234 | return (p*p * exp(-ekin/T)); | |
235 | } | |
236 | ||
237 | ||
238 | void AliGenSlowNucleons::Lorentz(Double_t m, Double_t beta, Float_t* q) | |
239 | { | |
240 | /* Lorentz transform in the direction of q[2] */ | |
241 | ||
242 | Double_t gamma = 1/sqrt(1-beta*beta); | |
243 | Double_t energy = sqrt(m*m + q[0]*q[0] + q[1]*q[1] + q[2]*q[2]); | |
244 | q[2] = gamma * (q[2] + beta*energy); | |
245 | } | |
246 | ||
247 | ||
248 | ||
249 | ||
250 | ||
251 | ||
252 |