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930c0bb5 | 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 | $Log$ | |
116cbefd | 18 | Revision 1.5 2003/01/07 14:11:43 morsch |
19 | Comminication with gray particle model and collision geometry added. | |
20 | ||
8b87aa60 | 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 | ||
ca33591a | 29 | Revision 1.2 2002/10/14 14:55:35 hristov |
30 | Merging the VirtualMC branch to the main development branch (HEAD) | |
31 | ||
b9d0a01d | 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 | ||
930c0bb5 | 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 | */ | |
116cbefd | 45 | |
46 | #include <TDatabasePDG.h> | |
47 | #include <TPDGCode.h> | |
48 | ||
49 | #include "AliCollisionGeometry.h" | |
930c0bb5 | 50 | #include "AliGenGrayParticles.h" |
c27c8b4d | 51 | #include "AliGrayParticleModel.h" |
930c0bb5 | 52 | |
53 | ClassImp(AliGenGrayParticles) | |
54 | ||
55 | AliGenGrayParticles::AliGenGrayParticles():AliGenerator(-1) | |
56 | { | |
57 | // Default constructor | |
8b87aa60 | 58 | fGrayParticleModel = 0; |
59 | fCollisionGeometry = 0; | |
930c0bb5 | 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(); | |
ca33591a | 71 | SetCharge(); |
930c0bb5 | 72 | SetTemperature(); |
ca33591a | 73 | SetBetaSource(); |
8b87aa60 | 74 | fGrayParticleModel = new AliGrayParticleModel(); |
75 | fCollisionGeometry = 0; | |
930c0bb5 | 76 | } |
77 | ||
78 | //____________________________________________________________ | |
79 | AliGenGrayParticles::~AliGenGrayParticles() | |
80 | { | |
81 | // Destructor | |
8b87aa60 | 82 | delete fGrayParticleModel; |
930c0bb5 | 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 | // | |
8b87aa60 | 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 | // | |
930c0bb5 | 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; | |
8b87aa60 | 117 | for(i = 0;i < fNpart; i++) { |
ca33591a | 118 | Int_t kf; |
119 | if(fCharge==1) kf = kProton; | |
120 | else kf = kNeutron; | |
121 | GenerateSlow(fCharge, fTemperature, fBetaSource, p); | |
930c0bb5 | 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 | ||
204 | ||
205 | ||
206 |