effc++ warnings
[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
803d1ab0 25/* $Id$ */
36b81802 26
27// Event generator of single e+e- pair production in ultraperipheral PbPb collisions
28// at 5.5 TeV/nucleon.
29// The generator is based on 5-dimentional differential cross section of the process.
30//%
31// References:
32// [1] "Multiple electromagnetic electron positron pair production in
33// relativistic heavy ion collisions".
34// Adrian Alscher, Kai Hencken, Dirk Trautmann, and Gerhard Baur,
35// Phys. Rev. A55 (1997) 396.
36// [2] K.Hencken, Yu.Kharlov, S.Sadovsky, Internal ALICE Note 2002-27.
37//%
38// Usage:
39// Initialization:
40// AliGenEpEmv1 *gener = new AliGenEpEmv1();
41// gener->SetXXXRange(); // Set kinematics range
42// gener->Init();
43// Event generation:
44// gener->Generate(); // Produce one e+e- pair with the event weight assigned
45// // to each track. The sum of event weights, divided by
46// // the total number of generated events, gives the
47// // integral cross section of the process of e+e- pair
48// // production in the above mentioned kinematics range.
49// // Sum of the selected event weights, divided by the total
50// // number of generated events, gives the integral cross
51// // section corresponded to the set of selected events
52//%
53// The generator consists of several modules:
54// 1) $ALICE_ROOT/EpEmGen/diffcross.f:
55// Exact calculation of the total differential e+ e- -pair production
56// in Relativistic Heavy Ion Collisions for a point particle in an
57// external field approach. See full comments in the mentioned file.
58// 2) $ALICE_ROOT/EpEmGen/epemgen.f:
59// Generator of e+e- pairs produced in PbPb collisions at LHC
60// it generates events according to the parametrization of the
61// differential cross section. Produces events have weights calculated
62// by the exact differential cross section calculation (diffcross.f).
63// See full comments in the mentioned file.
64// 3) Class TEpEmGen:
65// Interface from the fortran event generator to ALIROOT
66// 4) Class AliGenEpEmv1:
67// The event generator to call within ALIROOT
68//%
69// Author of this module: Yuri.Kharlov@cern.ch
70// 9 October 2002
71
72#include "AliGenEpEmv1.h"
73#include <TParticle.h>
74#include <TParticlePDG.h>
75#include <TDatabasePDG.h>
76#include <TEpEmGen.h>
77
78ClassImp(AliGenEpEmv1)
79
80//------------------------------------------------------------
81
82AliGenEpEmv1::AliGenEpEmv1()
83{
84 // Default constructor
85 // Avoid zero pt
86 if (fPtMin == 0) fPtMin = 1.E-04;
87}
88
89//____________________________________________________________
36b81802 90AliGenEpEmv1::~AliGenEpEmv1()
91{
92 // Destructor
93}
94
95//____________________________________________________________
96void AliGenEpEmv1::Init()
97{
98 // Initialisation:
99 // 1) define a generator
100 // 2) initialize the generator of e+e- pair production
101
102 fMass = TDatabasePDG::Instance()->GetParticle(11)->Mass();
103
104 SetMC(new TEpEmGen());
23a8d5be 105 fEpEmGen = (TEpEmGen*) fMCEvGen;
36b81802 106 fEpEmGen ->Initialize(fYMin,fYMax,fPtMin,fPtMax);
107 fEvent = 0;
108}
109
110//____________________________________________________________
111void AliGenEpEmv1::Generate()
112{
113 //
114 // Generate one e+e- pair
115 // Gaussian smearing on the vertex is done if selected.
116 //%
117 // Each produced e+e- pair is defined by the following variables:
118 // rapidities of e-, e+ (yElectron,yPositron)
119 // log10(pt in MeV/c) of e-, e+ (xElectron,xPositron)
120 // azymuth angles between e- and e+ (phi12)
121 //%
122 // On output an event weight is given (weight) which is assigned to each track.
123 // The sum of event weights, divided by the total number of generated events,
124 // gives the integral cross section of the e+e- pair production in the
125 // selected kinematics range.
126 //
127
128 Float_t polar[3]= {0,0,0};
129 Float_t origin[3];
130 Float_t p[3];
131
132 Double_t ptElectron,ptPositron, phiElectron,phiPositron, mt;
133 Double_t phi12=0,xElectron=0,xPositron=0,yElectron=0,yPositron=0,weight=0;
134 Int_t j, nt, id;
135 Float_t random[6];
136
137 fEpEmGen->GenerateEvent(fYMin,fYMax,fPtMin,fPtMax,
138 yElectron,yPositron,xElectron,xPositron,phi12,weight);
139 if (fDebug == 1)
140 printf("AliGenEpEmv1::Generate(): y=(%f,%f), x=(%f,%f), phi=%f\n",
141 yElectron,yPositron,xElectron,xPositron,phi12);
142
143 for (j=0;j<3;j++) origin[j]=fOrigin[j];
144 if(fVertexSmear==kPerEvent) {
145 Rndm(random,6);
146 for (j=0;j<3;j++) {
147 origin[j]+=fOsigma[j]*TMath::Cos(2*random[2*j]*TMath::Pi())*
148 TMath::Sqrt(-2*TMath::Log(random[2*j+1]));
149 }
150 }
151
152 Rndm(random,1);
153 ptElectron = TMath::Power(10,xElectron) * 1.e-03;;
154 ptPositron = TMath::Power(10,xPositron) * 1.e-03;;
155 phiElectron = fPhiMin + random[0] * (fPhiMax-fPhiMin);
156 phiPositron = phiElectron + phi12;
157
158 // Produce electron
159 mt = TMath::Sqrt(ptElectron*ptElectron + fMass*fMass);
160 p[0] = ptElectron*TMath::Cos(phiElectron);
161 p[1] = ptElectron*TMath::Sin(phiElectron);
162 p[2] = mt*TMath::SinH(yElectron);
163 id = 11;
164 if (fDebug == 2)
165 printf("id=%+3d, p = (%+11.4e,%+11.4e,%+11.4e) GeV\n",id,p[0],p[1],p[2]);
642f15cf 166 PushTrack(fTrackIt,-1, id,p,origin,polar,0,kPPrimary,nt,weight);
36b81802 167
168 // Produce positron
169 mt = TMath::Sqrt(ptPositron*ptPositron + fMass*fMass);
170 p[0] = ptPositron*TMath::Cos(phiPositron);
171 p[1] = ptPositron*TMath::Sin(phiPositron);
172 p[2] = mt*TMath::SinH(yPositron);
173 id = -11;
174 if (fDebug == 2)
175 printf("id=%+3d, p = (%+11.4e,%+11.4e,%+11.4e) GeV\n",id,p[0],p[1],p[2]);
642f15cf 176 PushTrack(fTrackIt,-1, id,p,origin,polar,0,kPPrimary,nt,weight);
36b81802 177
178 fEvent++;
179 if (fEvent%1000 == 0) {
180 printf("=====> AliGenEpEmv1::Generate(): \n Event %d, sigma=%f +- %f kb\n",
181 fEvent,fEpEmGen->GetXsection(),fEpEmGen->GetDsection());
182 }
183}
184