Coding Rule violations corrected.
[u/mrichter/AliRoot.git] / EVGEN / AliGenSlowNucleons.cxx
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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
88cb7938 16/* $Id$ */
c9a8628a 17
f687abfe 18//
19// Generator for slow nucleons in pA interactions.
20// Source is modelled by a relativistic Maxwell distributions.
21// This class cooparates with AliCollisionGeometry if used inside AliGenCocktail.
22// In this case the number of slow nucleons is determined from the number of wounded nuclei
23// using a realisation of AliSlowNucleonModel.
24// Original code by Ferenc Sikler <sikler@rmki.kfki.hu>
25//
c9a8628a 26
27#include <TDatabasePDG.h>
28#include <TPDGCode.h>
29#include <TH2F.h>
c8f7f6f9 30#include <TCanvas.h>
c9a8628a 31
32#include "AliCollisionGeometry.h"
33#include "AliGenSlowNucleons.h"
34#include "AliSlowNucleonModel.h"
35
36 ClassImp(AliGenSlowNucleons)
37
38 AliGenSlowNucleons::AliGenSlowNucleons():AliGenerator(-1)
39{
40// Default constructor
41 fSlowNucleonModel = 0;
42 fCollisionGeometry = 0;
43}
44
45AliGenSlowNucleons::AliGenSlowNucleons(Int_t npart)
46 :AliGenerator(npart)
47{
48// Constructor
49 fName = "SlowNucleons";
50 fTitle = "Generator for gray particles in pA collisions";
51 SetPmax();
52 SetTarget();
53 SetNominalCmsEnergy();
54 SetCharge();
55 SetTemperature();
56 SetBetaSource();
57 fSlowNucleonModel = new AliSlowNucleonModel();
58 fCollisionGeometry = 0;
59 fDebug = 0;
60}
61
f687abfe 62AliGenSlowNucleons::AliGenSlowNucleons(const AliGenSlowNucleons & sn):
63 AliGenerator(sn)
64{
65// Copy constructor
66 sn.Copy(*this);
67}
68
c9a8628a 69//____________________________________________________________
70AliGenSlowNucleons::~AliGenSlowNucleons()
71{
72// Destructor
73 delete fSlowNucleonModel;
74}
75
76
77void AliGenSlowNucleons::Init()
78{
79 //
80 // Initialization
81 //
82 Float_t kMass = TDatabasePDG::Instance()->GetParticle(kProton)->Mass();
83 fMomentum = fCMS/2. * fZTarget / fATarget;
84 fBeta = fMomentum / TMath::Sqrt(kMass * kMass + fMomentum * fMomentum);
85 if (fDebug) {
c8f7f6f9 86 fDebugHist1 = new TH2F("DebugHist1", "nu vs N_slow", 100, 0., 100., 20, 0., 20.);
87 fDebugHist2 = new TH2F("DebugHist2", "b vs N_slow", 100, 0., 100., 15, 0., 15.);
c9a8628a 88 }
89}
90
91void AliGenSlowNucleons::FinishRun()
92{
f687abfe 93// End of run action
94// Show histogram for debugging if requested.
c9a8628a 95 if (fDebug) {
c8f7f6f9 96 TCanvas *c = new TCanvas("c","Canvas 1",400,10,600,700);
97 c->Divide(2,1);
98 c->cd(1);
99 fDebugHist1->Draw();
100 c->cd(2);
101 fDebugHist2->Draw();
c9a8628a 102 }
103}
104
105
106void AliGenSlowNucleons::Generate()
107{
108 //
109 // Generate one event
110 //
111 //
112 // Communication with Gray Particle Model
113 //
1c22a81e 114 if (fCollisionGeometry) {
115 Float_t b = fCollisionGeometry->ImpactParameter();
116 Int_t nn = fCollisionGeometry->NN();
117 Int_t nwn = fCollisionGeometry->NwN();
118 Int_t nnw = fCollisionGeometry->NNw();
119 Int_t nwnw = fCollisionGeometry->NwNw();
120
99f5114f 121 fSlowNucleonModel->GetNumberOfSlowNucleons(fCollisionGeometry, fNgp, fNgn, fNbp, fNbn);
1c22a81e 122 if (fDebug) {
123 printf("Nucleons %d %d %d %d \n", fNgp, fNgn, fNbp, fNbn);
c8f7f6f9 124 fDebugHist1->Fill(Float_t(fNgp + fNgn + fNbp + fNbn), fCollisionGeometry->NwN(), 1.);
125 fDebugHist2->Fill(Float_t(fNgp + fNgn + fNbp + fNbn), b, 1.);
1c22a81e 126 printf("AliGenSlowNucleons: Impact parameter from Collision Geometry %f %d %d %d %d\n",
127 b, nn, nwn, nnw, nwnw);
128 }
129 }
c9a8628a 130
131 //
132 Float_t p[3];
133 Float_t origin[3] = {0., 0., 0.};
134 Float_t polar [3] = {0., 0., 0.};
99f5114f 135 Int_t nt, i, j;
c9a8628a 136 Int_t kf;
99f5114f 137
138 if(fVertexSmear == kPerEvent) {
139 Vertex();
140 for (j=0; j < 3; j++) origin[j] = fVertex[j];
141 } // if kPerEvent
c9a8628a 142//
143// Gray protons
144//
145 fCharge = 1;
146 kf = kProton;
1c22a81e 147 for(i = 0; i < fNgp; i++) {
c9a8628a 148 GenerateSlow(fCharge, fTemperatureG, fBetaSourceG, p);
642f15cf 149 PushTrack(fTrackIt, -1, kf, p, origin, polar,
c9a8628a 150 0., kPNoProcess, nt, 1.);
151 KeepTrack(nt);
152 }
153//
154// Gray neutrons
155//
156 fCharge = 0;
157 kf = kNeutron;
1c22a81e 158 for(i = 0; i < fNgn; i++) {
c9a8628a 159 GenerateSlow(fCharge, fTemperatureG, fBetaSourceG, p);
642f15cf 160 PushTrack(fTrackIt, -1, kf, p, origin, polar,
c9a8628a 161 0., kPNoProcess, nt, 1.);
162 KeepTrack(nt);
163 }
164//
165// Black protons
166//
167 fCharge = 1;
168 kf = kProton;
1c22a81e 169 for(i = 0; i < fNbp; i++) {
c9a8628a 170 GenerateSlow(fCharge, fTemperatureB, fBetaSourceB, p);
642f15cf 171 PushTrack(fTrackIt, -1, kf, p, origin, polar,
c9a8628a 172 0., kPNoProcess, nt, 1.);
173 KeepTrack(nt);
174 }
175//
176// Black neutrons
177//
178 fCharge = 0;
179 kf = kNeutron;
1c22a81e 180 for(i = 0; i < fNbn; i++) {
c9a8628a 181 GenerateSlow(fCharge, fTemperatureB, fBetaSourceB, p);
642f15cf 182 PushTrack(fTrackIt, -1, kf, p, origin, polar,
c9a8628a 183 0., kPNoProcess, nt, 1.);
184 KeepTrack(nt);
185 }
186}
187
188
189
190
191void AliGenSlowNucleons::GenerateSlow(Int_t charge, Double_t T, Double_t beta, Float_t* q)
f687abfe 192
193{
c9a8628a 194/*
195 Emit a slow nucleon with "temperature" T [GeV],
196 from a source moving with velocity beta
197 Three-momentum [GeV/c] is given back in q[3]
198*/
199
c9a8628a 200 Double_t m, pmax, p, f, theta, phi;
c9a8628a 201 TDatabasePDG * pdg = TDatabasePDG::Instance();
202 const Double_t kMassProton = pdg->GetParticle(kProton) ->Mass();
203 const Double_t kMassNeutron = pdg->GetParticle(kNeutron)->Mass();
204
205 /* Select nucleon type */
206 if(charge == 0) m = kMassNeutron;
207 else m = kMassProton;
208
209 /* Momentum at maximum of Maxwell-distribution */
210
211 pmax = TMath::Sqrt(2*T*(T+sqrt(T*T+m*m)));
212
213 /* Try until proper momentum */
214 /* for lack of primitive function of the Maxwell-distribution */
215 /* a brute force trial-accept loop, normalized at pmax */
216
217 do
218 {
219 p = Rndm() * fPmax;
220 f = Maxwell(m, p, T) / Maxwell(m , pmax, T);
221 }
222 while(f < Rndm());
223
224 /* Spherical symmetric emission */
225 theta = TMath::ACos(2. * Rndm() - 1.);
226 phi = 2. * TMath::Pi() * Rndm();
227
228 /* Determine momentum components in system of the moving source */
229 q[0] = p * TMath::Sin(theta) * TMath::Cos(phi);
230 q[1] = p * TMath::Sin(theta) * TMath::Sin(phi);
231 q[2] = p * TMath::Cos(theta);
232
233 /* Transform to system of the target nucleus */
234 /* beta is passed as negative, because the gray nucleons are slowed down */
235 Lorentz(m, -beta, q);
236
237 /* Transform to laboratory system */
238 Lorentz(m, fBeta, q);
239}
240
241Double_t AliGenSlowNucleons::Maxwell(Double_t m, Double_t p, Double_t T)
242{
243/* Relativistic Maxwell-distribution */
244 Double_t ekin;
245 ekin = TMath::Sqrt(p*p+m*m)-m;
246 return (p*p * exp(-ekin/T));
247}
248
249
250void AliGenSlowNucleons::Lorentz(Double_t m, Double_t beta, Float_t* q)
251{
252/* Lorentz transform in the direction of q[2] */
253
254 Double_t gamma = 1/sqrt(1-beta*beta);
255 Double_t energy = sqrt(m*m + q[0]*q[0] + q[1]*q[1] + q[2]*q[2]);
256 q[2] = gamma * (q[2] + beta*energy);
257}
258
f687abfe 259
260AliGenSlowNucleons& AliGenSlowNucleons::operator=(const AliGenSlowNucleons& rhs)
261{
262// Assignment operator
263 rhs.Copy(*this);
264 return *this;
265}
266
267void AliGenSlowNucleons::Copy(AliGenSlowNucleons&) const
268{
269 //
270 // Copy
271 //
272 Fatal("Copy","Not implemented!\n");
273}
274
c9a8628a 275
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