Use AliGrayParticleModel.
[u/mrichter/AliRoot.git] / EVGEN / AliGenGrayParticles.cxx
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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$Log$
c27c8b4d 18Revision 1.3 2002/12/02 10:02:40 morsch
19Corrections introduced by F. Silker:
20- SetBetaSource
21- Particle type according to charge.
22
ca33591a 23Revision 1.2 2002/10/14 14:55:35 hristov
24Merging the VirtualMC branch to the main development branch (HEAD)
25
b9d0a01d 26Revision 1.1.2.1 2002/10/10 16:40:08 hristov
27Updating VirtualMC to v3-09-02
28
29Revision 1.1 2002/10/08 13:53:17 morsch
30Gray particle generator, first commit.
31
930c0bb5 32*/
33
34/*
35 Generator for gray nucluons in pA interactions.
36 Source is modelled by a relativistic Maxwell distributions.
37 Original code by Ferenc Sikler <sikler@rmki.kfki.hu>
38 */
39#include "AliGenGrayParticles.h"
c27c8b4d 40#include "AliGrayParticleModel.h"
930c0bb5 41#include "AliPDG.h"
42#include <TDatabasePDG.h>
43
44 ClassImp(AliGenGrayParticles)
45
46 AliGenGrayParticles::AliGenGrayParticles():AliGenerator(-1)
47{
48// Default constructor
49}
50
51AliGenGrayParticles::AliGenGrayParticles(Int_t npart)
52 :AliGenerator(npart)
53{
54// Constructor
55 fName = "GrayParticles";
56 fTitle = "Generator for gray particles in pA collisions";
57 SetPmax();
58 SetTarget();
59 SetNominalCmsEnergy();
ca33591a 60 SetCharge();
930c0bb5 61 SetTemperature();
ca33591a 62 SetBetaSource();
930c0bb5 63}
64
65//____________________________________________________________
66AliGenGrayParticles::~AliGenGrayParticles()
67{
68// Destructor
69}
70
71
72void AliGenGrayParticles::Init()
73{
74 //
75 // Initialization
76 //
77 Float_t kMass = TDatabasePDG::Instance()->GetParticle(kProton)->Mass();
78 fMomentum = fCMS/2. * fZTarget / fATarget;
79 fBeta = fMomentum / TMath::Sqrt(kMass * kMass + fMomentum * fMomentum);
80}
81
82
83void AliGenGrayParticles::Generate()
84{
85 //
86 // Generate one event
87 //
88 Float_t p[3];
89 Float_t origin[3] = {0., 0., 0.};
90 Float_t polar [3] = {0., 0., 0.};
91 Int_t nt, i;
92 for(i = 0;i < fNpart; i++) {
ca33591a 93 Int_t kf;
94 if(fCharge==1) kf = kProton;
95 else kf = kNeutron;
96 GenerateSlow(fCharge, fTemperature, fBetaSource, p);
930c0bb5 97
98 SetTrack(fTrackIt, -1, kf, p, origin, polar,
99 0., kPNoProcess, nt, 1.);
100
101 KeepTrack(nt);
102 }
103}
104
105
106
107
108void AliGenGrayParticles::GenerateSlow(Int_t charge, Double_t T, Double_t beta, Float_t* q)
109/*
110 Emit a slow nucleon with "temperature" T [GeV],
111 from a source moving with velocity beta
112 Three-momentum [GeV/c] is given back in q[3]
113*/
114
115{
116 Double_t m, pmax, p, f, theta, phi;
117
118 TDatabasePDG * pdg = TDatabasePDG::Instance();
119 const Double_t kMassProton = pdg->GetParticle(kProton) ->Mass();
120 const Double_t kMassNeutron = pdg->GetParticle(kNeutron)->Mass();
121
122 /* Select nucleon type */
123 if(charge == 0) m = kMassNeutron;
124 else m = kMassProton;
125
126 /* Momentum at maximum of Maxwell-distribution */
127
128 pmax = TMath::Sqrt(2*T*(T+sqrt(T*T+m*m)));
129
130 /* Try until proper momentum */
131 /* for lack of primitive function of the Maxwell-distribution */
132 /* a brute force trial-accept loop, normalized at pmax */
133
134 do
135 {
136 p = Rndm() * fPmax;
137 f = Maxwell(m, p, T) / Maxwell(m , pmax, T);
138 }
139 while(f < Rndm());
140
141 /* Spherical symmetric emission */
142 theta = TMath::ACos(2. * Rndm() - 1.);
143 phi = 2. * TMath::Pi() * Rndm();
144
145 /* Determine momentum components in system of the moving source */
146 q[0] = p * TMath::Sin(theta) * TMath::Cos(phi);
147 q[1] = p * TMath::Sin(theta) * TMath::Sin(phi);
148 q[2] = p * TMath::Cos(theta);
149
150 /* Transform to system of the target nucleus */
151 /* beta is passed as negative, because the gray nucleons are slowed down */
152 Lorentz(m, -beta, q);
153
154 /* Transform to laboratory system */
155 Lorentz(m, fBeta, q);
156}
157
158Double_t AliGenGrayParticles::Maxwell(Double_t m, Double_t p, Double_t T)
159{
160/* Relativistic Maxwell-distribution */
161 Double_t ekin;
162 ekin = TMath::Sqrt(p*p+m*m)-m;
163 return (p*p * exp(-ekin/T));
164}
165
166
167void AliGenGrayParticles::Lorentz(Double_t m, Double_t beta, Float_t* q)
168{
169/* Lorentz transform in the direction of q[2] */
170
171 Double_t gamma = 1/sqrt(1-beta*beta);
172 Double_t energy = sqrt(m*m + q[0]*q[0] + q[1]*q[1] + q[2]*q[2]);
173 q[2] = gamma * (q[2] + beta*energy);
174}
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