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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 | ||
16 | /* | |
17 | $Log$ | |
18 | */ | |
19 | ||
20 | /* | |
21 | Generator for slow nucluons in pA interactions. | |
22 | Source is modelled by a relativistic Maxwell distributions. | |
23 | Original code by Ferenc Sikler <sikler@rmki.kfki.hu> | |
24 | */ | |
25 | ||
26 | #include <TDatabasePDG.h> | |
27 | #include <TPDGCode.h> | |
28 | #include <TH2F.h> | |
29 | ||
30 | #include "AliCollisionGeometry.h" | |
31 | #include "AliGenSlowNucleons.h" | |
32 | #include "AliSlowNucleonModel.h" | |
33 | ||
34 | ClassImp(AliGenSlowNucleons) | |
35 | ||
36 | AliGenSlowNucleons::AliGenSlowNucleons():AliGenerator(-1) | |
37 | { | |
38 | // Default constructor | |
39 | fSlowNucleonModel = 0; | |
40 | fCollisionGeometry = 0; | |
41 | } | |
42 | ||
43 | AliGenSlowNucleons::AliGenSlowNucleons(Int_t npart) | |
44 | :AliGenerator(npart) | |
45 | { | |
46 | // Constructor | |
47 | fName = "SlowNucleons"; | |
48 | fTitle = "Generator for gray particles in pA collisions"; | |
49 | SetPmax(); | |
50 | SetTarget(); | |
51 | SetNominalCmsEnergy(); | |
52 | SetCharge(); | |
53 | SetTemperature(); | |
54 | SetBetaSource(); | |
55 | fSlowNucleonModel = new AliSlowNucleonModel(); | |
56 | fCollisionGeometry = 0; | |
57 | fDebug = 0; | |
58 | } | |
59 | ||
60 | //____________________________________________________________ | |
61 | AliGenSlowNucleons::~AliGenSlowNucleons() | |
62 | { | |
63 | // Destructor | |
64 | delete fSlowNucleonModel; | |
65 | } | |
66 | ||
67 | ||
68 | void AliGenSlowNucleons::Init() | |
69 | { | |
70 | // | |
71 | // Initialization | |
72 | // | |
73 | Float_t kMass = TDatabasePDG::Instance()->GetParticle(kProton)->Mass(); | |
74 | fMomentum = fCMS/2. * fZTarget / fATarget; | |
75 | fBeta = fMomentum / TMath::Sqrt(kMass * kMass + fMomentum * fMomentum); | |
76 | if (fDebug) { | |
77 | fDebugHist = new TH2F("DebugHist", "N_heavy vs nu", 50, 0., 50., 50, 0., 50.); | |
78 | } | |
79 | } | |
80 | ||
81 | void AliGenSlowNucleons::FinishRun() | |
82 | { | |
83 | if (fDebug) { | |
84 | fDebugHist->Draw(); | |
85 | } | |
86 | } | |
87 | ||
88 | ||
89 | void AliGenSlowNucleons::Generate() | |
90 | { | |
91 | // | |
92 | // Generate one event | |
93 | // | |
94 | // | |
95 | // Communication with Gray Particle Model | |
96 | // | |
97 | Int_t ngp, ngn, nbp, nbn; | |
98 | ||
99 | Float_t b = fCollisionGeometry->ImpactParameter(); | |
100 | Int_t nn = fCollisionGeometry->NN(); | |
101 | Int_t nwn = fCollisionGeometry->NwN(); | |
102 | Int_t nnw = fCollisionGeometry->NNw(); | |
103 | Int_t nwnw = fCollisionGeometry->NwNw(); | |
104 | ||
105 | printf("AliGenSlowNucleons: Impact parameter from Collision Geometry %f %d %d %d %d\n", | |
106 | b, nn, nwn, nnw, nwnw); | |
107 | ||
108 | fSlowNucleonModel->GetNumberOfSlowNucleons(fCollisionGeometry, ngp, ngn, nbp, nbn); | |
109 | ||
110 | if (fDebug) { | |
111 | printf("nucleons %d %d %d %d \n", ngp, ngn, nbp, nbn); | |
112 | ||
113 | fDebugHist->Fill(Float_t(ngp + ngn + nbp + nbn), fCollisionGeometry->NwN(), 1.); | |
114 | } | |
115 | ||
116 | ||
117 | // | |
118 | Float_t p[3]; | |
119 | Float_t origin[3] = {0., 0., 0.}; | |
120 | Float_t polar [3] = {0., 0., 0.}; | |
121 | Int_t nt, i; | |
122 | Int_t kf; | |
123 | // | |
124 | // Gray protons | |
125 | // | |
126 | fCharge = 1; | |
127 | kf = kProton; | |
128 | for(i = 0; i < ngp; i++) { | |
129 | GenerateSlow(fCharge, fTemperatureG, fBetaSourceG, p); | |
130 | SetTrack(fTrackIt, -1, kf, p, origin, polar, | |
131 | 0., kPNoProcess, nt, 1.); | |
132 | KeepTrack(nt); | |
133 | } | |
134 | // | |
135 | // Gray neutrons | |
136 | // | |
137 | fCharge = 0; | |
138 | kf = kNeutron; | |
139 | for(i = 0; i < ngn; i++) { | |
140 | GenerateSlow(fCharge, fTemperatureG, fBetaSourceG, p); | |
141 | SetTrack(fTrackIt, -1, kf, p, origin, polar, | |
142 | 0., kPNoProcess, nt, 1.); | |
143 | KeepTrack(nt); | |
144 | } | |
145 | // | |
146 | // Black protons | |
147 | // | |
148 | fCharge = 1; | |
149 | kf = kProton; | |
150 | for(i = 0; i < nbp; i++) { | |
151 | GenerateSlow(fCharge, fTemperatureB, fBetaSourceB, p); | |
152 | SetTrack(fTrackIt, -1, kf, p, origin, polar, | |
153 | 0., kPNoProcess, nt, 1.); | |
154 | KeepTrack(nt); | |
155 | } | |
156 | // | |
157 | // Black neutrons | |
158 | // | |
159 | fCharge = 0; | |
160 | kf = kNeutron; | |
161 | for(i = 0; i < nbn; i++) { | |
162 | GenerateSlow(fCharge, fTemperatureB, fBetaSourceB, p); | |
163 | SetTrack(fTrackIt, -1, kf, p, origin, polar, | |
164 | 0., kPNoProcess, nt, 1.); | |
165 | KeepTrack(nt); | |
166 | } | |
167 | } | |
168 | ||
169 | ||
170 | ||
171 | ||
172 | void AliGenSlowNucleons::GenerateSlow(Int_t charge, Double_t T, Double_t beta, Float_t* q) | |
173 | /* | |
174 | Emit a slow nucleon with "temperature" T [GeV], | |
175 | from a source moving with velocity beta | |
176 | Three-momentum [GeV/c] is given back in q[3] | |
177 | */ | |
178 | ||
179 | { | |
180 | Double_t m, pmax, p, f, theta, phi; | |
181 | ||
182 | TDatabasePDG * pdg = TDatabasePDG::Instance(); | |
183 | const Double_t kMassProton = pdg->GetParticle(kProton) ->Mass(); | |
184 | const Double_t kMassNeutron = pdg->GetParticle(kNeutron)->Mass(); | |
185 | ||
186 | /* Select nucleon type */ | |
187 | if(charge == 0) m = kMassNeutron; | |
188 | else m = kMassProton; | |
189 | ||
190 | /* Momentum at maximum of Maxwell-distribution */ | |
191 | ||
192 | pmax = TMath::Sqrt(2*T*(T+sqrt(T*T+m*m))); | |
193 | ||
194 | /* Try until proper momentum */ | |
195 | /* for lack of primitive function of the Maxwell-distribution */ | |
196 | /* a brute force trial-accept loop, normalized at pmax */ | |
197 | ||
198 | do | |
199 | { | |
200 | p = Rndm() * fPmax; | |
201 | f = Maxwell(m, p, T) / Maxwell(m , pmax, T); | |
202 | } | |
203 | while(f < Rndm()); | |
204 | ||
205 | /* Spherical symmetric emission */ | |
206 | theta = TMath::ACos(2. * Rndm() - 1.); | |
207 | phi = 2. * TMath::Pi() * Rndm(); | |
208 | ||
209 | /* Determine momentum components in system of the moving source */ | |
210 | q[0] = p * TMath::Sin(theta) * TMath::Cos(phi); | |
211 | q[1] = p * TMath::Sin(theta) * TMath::Sin(phi); | |
212 | q[2] = p * TMath::Cos(theta); | |
213 | ||
214 | /* Transform to system of the target nucleus */ | |
215 | /* beta is passed as negative, because the gray nucleons are slowed down */ | |
216 | Lorentz(m, -beta, q); | |
217 | ||
218 | /* Transform to laboratory system */ | |
219 | Lorentz(m, fBeta, q); | |
220 | } | |
221 | ||
222 | Double_t AliGenSlowNucleons::Maxwell(Double_t m, Double_t p, Double_t T) | |
223 | { | |
224 | /* Relativistic Maxwell-distribution */ | |
225 | Double_t ekin; | |
226 | ekin = TMath::Sqrt(p*p+m*m)-m; | |
227 | return (p*p * exp(-ekin/T)); | |
228 | } | |
229 | ||
230 | ||
231 | void AliGenSlowNucleons::Lorentz(Double_t m, Double_t beta, Float_t* q) | |
232 | { | |
233 | /* Lorentz transform in the direction of q[2] */ | |
234 | ||
235 | Double_t gamma = 1/sqrt(1-beta*beta); | |
236 | Double_t energy = sqrt(m*m + q[0]*q[0] + q[1]*q[1] + q[2]*q[2]); | |
237 | q[2] = gamma * (q[2] + beta*energy); | |
238 | } | |
239 | ||
240 | ||
241 | ||
242 | ||
243 | ||
244 | ||
245 |