Classes imported from EVGEN
[u/mrichter/AliRoot.git] / TEPEMGEN / AliGenEpEmv1.cxx
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36b81802 1/**************************************************************************
2 * Copyright(c) 1998-2002, 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 * Copyright(c) 1997, 1998, 2002, Adrian Alscher and Kai Hencken *
17 * See $ALICE_ROOT/EpEmGen/diffcross.f for full Copyright notice *
18 * *
19 * *
20 * Copyright(c) 2002 Kai Hencken, Yuri Kharlov, Serguei Sadovsky *
21 * See $ALICE_ROOT/EpEmGen/epemgen.f for full Copyright notice *
22 * *
23 **************************************************************************/
24
25/*
26$Log$
27Revision 1.1 2002/11/06 10:26:45 hristov
28Event generator for e+e- pair production (Yu.Kharlov)
29
30*/
31
32// Event generator of single e+e- pair production in ultraperipheral PbPb collisions
33// at 5.5 TeV/nucleon.
34// The generator is based on 5-dimentional differential cross section of the process.
35//%
36// References:
37// [1] "Multiple electromagnetic electron positron pair production in
38// relativistic heavy ion collisions".
39// Adrian Alscher, Kai Hencken, Dirk Trautmann, and Gerhard Baur,
40// Phys. Rev. A55 (1997) 396.
41// [2] K.Hencken, Yu.Kharlov, S.Sadovsky, Internal ALICE Note 2002-27.
42//%
43// Usage:
44// Initialization:
45// AliGenEpEmv1 *gener = new AliGenEpEmv1();
46// gener->SetXXXRange(); // Set kinematics range
47// gener->Init();
48// Event generation:
49// gener->Generate(); // Produce one e+e- pair with the event weight assigned
50// // to each track. The sum of event weights, divided by
51// // the total number of generated events, gives the
52// // integral cross section of the process of e+e- pair
53// // production in the above mentioned kinematics range.
54// // Sum of the selected event weights, divided by the total
55// // number of generated events, gives the integral cross
56// // section corresponded to the set of selected events
57//%
58// The generator consists of several modules:
59// 1) $ALICE_ROOT/EpEmGen/diffcross.f:
60// Exact calculation of the total differential e+ e- -pair production
61// in Relativistic Heavy Ion Collisions for a point particle in an
62// external field approach. See full comments in the mentioned file.
63// 2) $ALICE_ROOT/EpEmGen/epemgen.f:
64// Generator of e+e- pairs produced in PbPb collisions at LHC
65// it generates events according to the parametrization of the
66// differential cross section. Produces events have weights calculated
67// by the exact differential cross section calculation (diffcross.f).
68// See full comments in the mentioned file.
69// 3) Class TEpEmGen:
70// Interface from the fortran event generator to ALIROOT
71// 4) Class AliGenEpEmv1:
72// The event generator to call within ALIROOT
73//%
74// Author of this module: Yuri.Kharlov@cern.ch
75// 9 October 2002
76
77#include "AliGenEpEmv1.h"
78#include <TParticle.h>
79#include <TParticlePDG.h>
80#include <TDatabasePDG.h>
81#include <TEpEmGen.h>
82
83ClassImp(AliGenEpEmv1)
84
85//------------------------------------------------------------
86
87AliGenEpEmv1::AliGenEpEmv1()
88{
89 // Default constructor
90 // Avoid zero pt
91 if (fPtMin == 0) fPtMin = 1.E-04;
92}
93
94//____________________________________________________________
95AliGenEpEmv1::AliGenEpEmv1(const AliGenEpEmv1 & gen)
96{
97 // copy constructor
98 gen.Copy(*this);
99}
100
101//____________________________________________________________
102AliGenEpEmv1::~AliGenEpEmv1()
103{
104 // Destructor
105}
106
107//____________________________________________________________
108void AliGenEpEmv1::Init()
109{
110 // Initialisation:
111 // 1) define a generator
112 // 2) initialize the generator of e+e- pair production
113
114 fMass = TDatabasePDG::Instance()->GetParticle(11)->Mass();
115
116 SetMC(new TEpEmGen());
117 fEpEmGen = (TEpEmGen*) fgMCEvGen;
118 fEpEmGen ->Initialize(fYMin,fYMax,fPtMin,fPtMax);
119 fEvent = 0;
120}
121
122//____________________________________________________________
123void AliGenEpEmv1::Generate()
124{
125 //
126 // Generate one e+e- pair
127 // Gaussian smearing on the vertex is done if selected.
128 //%
129 // Each produced e+e- pair is defined by the following variables:
130 // rapidities of e-, e+ (yElectron,yPositron)
131 // log10(pt in MeV/c) of e-, e+ (xElectron,xPositron)
132 // azymuth angles between e- and e+ (phi12)
133 //%
134 // On output an event weight is given (weight) which is assigned to each track.
135 // The sum of event weights, divided by the total number of generated events,
136 // gives the integral cross section of the e+e- pair production in the
137 // selected kinematics range.
138 //
139
140 Float_t polar[3]= {0,0,0};
141 Float_t origin[3];
142 Float_t p[3];
143
144 Double_t ptElectron,ptPositron, phiElectron,phiPositron, mt;
145 Double_t phi12=0,xElectron=0,xPositron=0,yElectron=0,yPositron=0,weight=0;
146 Int_t j, nt, id;
147 Float_t random[6];
148
149 fEpEmGen->GenerateEvent(fYMin,fYMax,fPtMin,fPtMax,
150 yElectron,yPositron,xElectron,xPositron,phi12,weight);
151 if (fDebug == 1)
152 printf("AliGenEpEmv1::Generate(): y=(%f,%f), x=(%f,%f), phi=%f\n",
153 yElectron,yPositron,xElectron,xPositron,phi12);
154
155 for (j=0;j<3;j++) origin[j]=fOrigin[j];
156 if(fVertexSmear==kPerEvent) {
157 Rndm(random,6);
158 for (j=0;j<3;j++) {
159 origin[j]+=fOsigma[j]*TMath::Cos(2*random[2*j]*TMath::Pi())*
160 TMath::Sqrt(-2*TMath::Log(random[2*j+1]));
161 }
162 }
163
164 Rndm(random,1);
165 ptElectron = TMath::Power(10,xElectron) * 1.e-03;;
166 ptPositron = TMath::Power(10,xPositron) * 1.e-03;;
167 phiElectron = fPhiMin + random[0] * (fPhiMax-fPhiMin);
168 phiPositron = phiElectron + phi12;
169
170 // Produce electron
171 mt = TMath::Sqrt(ptElectron*ptElectron + fMass*fMass);
172 p[0] = ptElectron*TMath::Cos(phiElectron);
173 p[1] = ptElectron*TMath::Sin(phiElectron);
174 p[2] = mt*TMath::SinH(yElectron);
175 id = 11;
176 if (fDebug == 2)
177 printf("id=%+3d, p = (%+11.4e,%+11.4e,%+11.4e) GeV\n",id,p[0],p[1],p[2]);
178 SetTrack(fTrackIt,-1, id,p,origin,polar,0,kPPrimary,nt,weight);
179
180 // Produce positron
181 mt = TMath::Sqrt(ptPositron*ptPositron + fMass*fMass);
182 p[0] = ptPositron*TMath::Cos(phiPositron);
183 p[1] = ptPositron*TMath::Sin(phiPositron);
184 p[2] = mt*TMath::SinH(yPositron);
185 id = -11;
186 if (fDebug == 2)
187 printf("id=%+3d, p = (%+11.4e,%+11.4e,%+11.4e) GeV\n",id,p[0],p[1],p[2]);
188 SetTrack(fTrackIt,-1, id,p,origin,polar,0,kPPrimary,nt,weight);
189
190 fEvent++;
191 if (fEvent%1000 == 0) {
192 printf("=====> AliGenEpEmv1::Generate(): \n Event %d, sigma=%f +- %f kb\n",
193 fEvent,fEpEmGen->GetXsection(),fEpEmGen->GetDsection());
194 }
195}
196