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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 | $Log$ |
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18 | Revision 1.5 2003/01/07 14:11:43 morsch |
19 | Comminication with gray particle model and collision geometry added. |
20 | |
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21 | Revision 1.4 2003/01/06 10:09:57 morsch |
22 | Use AliGrayParticleModel. |
23 | |
c27c8b4d |
24 | Revision 1.3 2002/12/02 10:02:40 morsch |
25 | Corrections introduced by F. Silker: |
26 | - SetBetaSource |
27 | - Particle type according to charge. |
28 | |
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29 | Revision 1.2 2002/10/14 14:55:35 hristov |
30 | Merging the VirtualMC branch to the main development branch (HEAD) |
31 | |
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32 | Revision 1.1.2.1 2002/10/10 16:40:08 hristov |
33 | Updating VirtualMC to v3-09-02 |
34 | |
35 | Revision 1.1 2002/10/08 13:53:17 morsch |
36 | Gray particle generator, first commit. |
37 | |
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38 | */ |
39 | |
40 | /* |
41 | Generator for gray nucluons in pA interactions. |
42 | Source is modelled by a relativistic Maxwell distributions. |
43 | Original code by Ferenc Sikler <sikler@rmki.kfki.hu> |
44 | */ |
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45 | |
46 | #include <TDatabasePDG.h> |
47 | #include <TPDGCode.h> |
48 | |
49 | #include "AliCollisionGeometry.h" |
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50 | #include "AliGenGrayParticles.h" |
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51 | #include "AliGrayParticleModel.h" |
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52 | |
53 | ClassImp(AliGenGrayParticles) |
54 | |
55 | AliGenGrayParticles::AliGenGrayParticles():AliGenerator(-1) |
56 | { |
57 | // Default constructor |
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58 | fGrayParticleModel = 0; |
59 | fCollisionGeometry = 0; |
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60 | } |
61 | |
62 | AliGenGrayParticles::AliGenGrayParticles(Int_t npart) |
63 | :AliGenerator(npart) |
64 | { |
65 | // Constructor |
66 | fName = "GrayParticles"; |
67 | fTitle = "Generator for gray particles in pA collisions"; |
68 | SetPmax(); |
69 | SetTarget(); |
70 | SetNominalCmsEnergy(); |
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71 | SetCharge(); |
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72 | SetTemperature(); |
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73 | SetBetaSource(); |
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74 | fGrayParticleModel = new AliGrayParticleModel(); |
75 | fCollisionGeometry = 0; |
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76 | } |
77 | |
78 | //____________________________________________________________ |
79 | AliGenGrayParticles::~AliGenGrayParticles() |
80 | { |
81 | // Destructor |
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82 | delete fGrayParticleModel; |
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83 | } |
84 | |
85 | |
86 | void AliGenGrayParticles::Init() |
87 | { |
88 | // |
89 | // Initialization |
90 | // |
91 | Float_t kMass = TDatabasePDG::Instance()->GetParticle(kProton)->Mass(); |
92 | fMomentum = fCMS/2. * fZTarget / fATarget; |
93 | fBeta = fMomentum / TMath::Sqrt(kMass * kMass + fMomentum * fMomentum); |
94 | } |
95 | |
96 | |
97 | void AliGenGrayParticles::Generate() |
98 | { |
99 | // |
100 | // Generate one event |
101 | // |
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102 | // |
103 | // Communication with Gray Particle Model |
104 | // |
105 | Int_t np, nn; |
106 | |
107 | Float_t b = fCollisionGeometry->ImpactParameter(); |
108 | printf("AliGenGrayParticles: Impact parameter from Collision Geometry %f \n", b); |
109 | |
110 | fGrayParticleModel->GetNumberOfGrayNucleons(fCollisionGeometry, np, nn); |
111 | |
112 | // |
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113 | Float_t p[3]; |
114 | Float_t origin[3] = {0., 0., 0.}; |
115 | Float_t polar [3] = {0., 0., 0.}; |
116 | Int_t nt, i; |
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117 | for(i = 0;i < fNpart; i++) { |
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118 | Int_t kf; |
119 | if(fCharge==1) kf = kProton; |
120 | else kf = kNeutron; |
121 | GenerateSlow(fCharge, fTemperature, fBetaSource, p); |
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122 | |
123 | SetTrack(fTrackIt, -1, kf, p, origin, polar, |
124 | 0., kPNoProcess, nt, 1.); |
125 | |
126 | KeepTrack(nt); |
127 | } |
128 | } |
129 | |
130 | |
131 | |
132 | |
133 | void AliGenGrayParticles::GenerateSlow(Int_t charge, Double_t T, Double_t beta, Float_t* q) |
134 | /* |
135 | Emit a slow nucleon with "temperature" T [GeV], |
136 | from a source moving with velocity beta |
137 | Three-momentum [GeV/c] is given back in q[3] |
138 | */ |
139 | |
140 | { |
141 | Double_t m, pmax, p, f, theta, phi; |
142 | |
143 | TDatabasePDG * pdg = TDatabasePDG::Instance(); |
144 | const Double_t kMassProton = pdg->GetParticle(kProton) ->Mass(); |
145 | const Double_t kMassNeutron = pdg->GetParticle(kNeutron)->Mass(); |
146 | |
147 | /* Select nucleon type */ |
148 | if(charge == 0) m = kMassNeutron; |
149 | else m = kMassProton; |
150 | |
151 | /* Momentum at maximum of Maxwell-distribution */ |
152 | |
153 | pmax = TMath::Sqrt(2*T*(T+sqrt(T*T+m*m))); |
154 | |
155 | /* Try until proper momentum */ |
156 | /* for lack of primitive function of the Maxwell-distribution */ |
157 | /* a brute force trial-accept loop, normalized at pmax */ |
158 | |
159 | do |
160 | { |
161 | p = Rndm() * fPmax; |
162 | f = Maxwell(m, p, T) / Maxwell(m , pmax, T); |
163 | } |
164 | while(f < Rndm()); |
165 | |
166 | /* Spherical symmetric emission */ |
167 | theta = TMath::ACos(2. * Rndm() - 1.); |
168 | phi = 2. * TMath::Pi() * Rndm(); |
169 | |
170 | /* Determine momentum components in system of the moving source */ |
171 | q[0] = p * TMath::Sin(theta) * TMath::Cos(phi); |
172 | q[1] = p * TMath::Sin(theta) * TMath::Sin(phi); |
173 | q[2] = p * TMath::Cos(theta); |
174 | |
175 | /* Transform to system of the target nucleus */ |
176 | /* beta is passed as negative, because the gray nucleons are slowed down */ |
177 | Lorentz(m, -beta, q); |
178 | |
179 | /* Transform to laboratory system */ |
180 | Lorentz(m, fBeta, q); |
181 | } |
182 | |
183 | Double_t AliGenGrayParticles::Maxwell(Double_t m, Double_t p, Double_t T) |
184 | { |
185 | /* Relativistic Maxwell-distribution */ |
186 | Double_t ekin; |
187 | ekin = TMath::Sqrt(p*p+m*m)-m; |
188 | return (p*p * exp(-ekin/T)); |
189 | } |
190 | |
191 | |
192 | void AliGenGrayParticles::Lorentz(Double_t m, Double_t beta, Float_t* q) |
193 | { |
194 | /* Lorentz transform in the direction of q[2] */ |
195 | |
196 | Double_t gamma = 1/sqrt(1-beta*beta); |
197 | Double_t energy = sqrt(m*m + q[0]*q[0] + q[1]*q[1] + q[2]*q[2]); |
198 | q[2] = gamma * (q[2] + beta*energy); |
199 | } |
200 | |
201 | |
202 | |
203 | |
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205 | |
206 | |