1 /**************************************************************************
2 * Copyright(c) 1998-2002, ALICE Experiment at CERN, All rights reserved. *
4 * Author: The ALICE Off-line Project. *
5 * Contributors are mentioned in the code where appropriate. *
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. *
16 * Copyright(c) 1997, 1998, 2002, Adrian Alscher and Kai Hencken *
17 * See $ALICE_ROOT/EpEmGen/diffcross.f for full Copyright notice *
20 * Copyright(c) 2002 Kai Hencken, Yuri Kharlov, Serguei Sadovsky *
21 * See $ALICE_ROOT/EpEmGen/epemgen.f for full Copyright notice *
23 **************************************************************************/
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.
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.
40 // AliGenEpEmv1 *gener = new AliGenEpEmv1();
41 // gener->SetXXXRange(); // Set kinematics range
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
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.
65 // Interface from the fortran event generator to ALIROOT
66 // 4) Class AliGenEpEmv1:
67 // The event generator to call within ALIROOT
69 // Author of this module: Yuri.Kharlov@cern.ch
72 #include "AliGenEpEmv1.h"
73 #include <TParticle.h>
74 #include <TParticlePDG.h>
75 #include <TDatabasePDG.h>
78 ClassImp(AliGenEpEmv1)
80 //------------------------------------------------------------
82 AliGenEpEmv1::AliGenEpEmv1():
87 fHeader(AliGenEventHeader())
89 // Default constructor
91 if (fPtMin == 0) fPtMin = 1.E-04;
94 //____________________________________________________________
95 AliGenEpEmv1::~AliGenEpEmv1()
100 //____________________________________________________________
101 void AliGenEpEmv1::Init()
104 // 1) define a generator
105 // 2) initialize the generator of e+e- pair production
107 fMass = TDatabasePDG::Instance()->GetParticle(11)->Mass();
109 SetMC(new TEpEmGen());
110 fEpEmGen = (TEpEmGen*) fMCEvGen;
111 fEpEmGen ->Initialize(fYMin,fYMax,fPtMin,fPtMax);
115 //____________________________________________________________
116 void AliGenEpEmv1::Generate()
119 // Generate one e+e- pair
120 // Gaussian smearing on the vertex is done if selected.
122 // Each produced e+e- pair is defined by the following variables:
123 // rapidities of e-, e+ (yElectron,yPositron)
124 // log10(pt in MeV/c) of e-, e+ (xElectron,xPositron)
125 // azymuth angles between e- and e+ (phi12)
127 // On output an event weight is given (weight) which is assigned to each track.
128 // The sum of event weights, divided by the total number of generated events,
129 // gives the integral cross section of the e+e- pair production in the
130 // selected kinematics range.
133 Float_t polar[3]= {0,0,0};
138 Double_t ptElectron,ptPositron, phiElectron,phiPositron, mt;
139 Double_t phi12=0,xElectron=0,xPositron=0,yElectron=0,yPositron=0,weight=0;
143 fEpEmGen->GenerateEvent(fYMin,fYMax,fPtMin,fPtMax,
144 yElectron,yPositron,xElectron,xPositron,phi12,weight);
146 printf("AliGenEpEmv1::Generate(): y=(%f,%f), x=(%f,%f), phi=%f\n",
147 yElectron,yPositron,xElectron,xPositron,phi12);
149 for (j=0;j<3;j++) origin[j]=fOrigin[j];
151 if(fVertexSmear==kPerEvent) {
154 origin[j]+=fOsigma[j]*TMath::Cos(2*random[2*j]*TMath::Pi())*
155 TMath::Sqrt(-2*TMath::Log(random[2*j+1]));
158 time += fOsigma[2]/TMath::Ccgs()*
159 TMath::Cos(2*random[0]*TMath::Pi())*
160 TMath::Sqrt(-2*TMath::Log(random[1]));
164 ptElectron = TMath::Power(10,xElectron) * 1.e-03;;
165 ptPositron = TMath::Power(10,xPositron) * 1.e-03;;
166 phiElectron = fPhiMin + random[0] * (fPhiMax-fPhiMin);
167 phiPositron = phiElectron + phi12;
170 mt = TMath::Sqrt(ptElectron*ptElectron + fMass*fMass);
171 p[0] = ptElectron*TMath::Cos(phiElectron);
172 p[1] = ptElectron*TMath::Sin(phiElectron);
173 p[2] = mt*TMath::SinH(yElectron);
176 printf("id=%+3d, p = (%+11.4e,%+11.4e,%+11.4e) GeV\n",id,p[0],p[1],p[2]);
177 PushTrack(fTrackIt,-1, id,p,origin,polar,time,kPPrimary,nt,weight);
180 mt = TMath::Sqrt(ptPositron*ptPositron + fMass*fMass);
181 p[0] = ptPositron*TMath::Cos(phiPositron);
182 p[1] = ptPositron*TMath::Sin(phiPositron);
183 p[2] = mt*TMath::SinH(yPositron);
186 printf("id=%+3d, p = (%+11.4e,%+11.4e,%+11.4e) GeV\n",id,p[0],p[1],p[2]);
187 PushTrack(fTrackIt,-1, id,p,origin,polar,time,kPPrimary,nt,weight);
190 if (fEvent%1000 == 0) {
191 printf("=====> AliGenEpEmv1::Generate(): \n Event %d, sigma=%f +- %f kb\n",
192 fEvent,fEpEmGen->GetXsection(),fEpEmGen->GetDsection());
194 fHeader.SetEventWeight(weight);
195 fHeader.SetInteractionTime(time);