--- /dev/null
+/**************************************************************************
+ * Copyright(c) 1998-2002, ALICE Experiment at CERN, All rights reserved. *
+ * *
+ * Author: The ALICE Off-line Project. *
+ * Contributors are mentioned in the code where appropriate. *
+ * *
+ * Permission to use, copy, modify and distribute this software and its *
+ * documentation strictly for non-commercial purposes is hereby granted *
+ * without fee, provided that the above copyright notice appears in all *
+ * copies and that both the copyright notice and this permission notice *
+ * appear in the supporting documentation. The authors make no claims *
+ * about the suitability of this software for any purpose. It is *
+ * provided "as is" without express or implied warranty. *
+ * *
+ * *
+ * Copyright(c) 1997, 1998, 2002, Adrian Alscher and Kai Hencken *
+ * See $ALICE_ROOT/EpEmGen/diffcross.f for full Copyright notice *
+ * *
+ * *
+ * Copyright(c) 2002 Kai Hencken, Yuri Kharlov, Serguei Sadovsky *
+ * See $ALICE_ROOT/EpEmGen/epemgen.f for full Copyright notice *
+ * *
+ **************************************************************************/
+
+/* $Id$ */
+
+// Event generator for background from e+e- pair production in ultraperipheral PbPb collisions
+// at 5.5 TeV/nucleon, integrated over specific readout cycle
+// Derived from AliGenEpEmv1
+// Author: ruben.shahoyan@cern.ch
+//%
+// References:
+// [1] "Multiple electromagnetic electron positron pair production in
+// relativistic heavy ion collisions".
+// Adrian Alscher, Kai Hencken, Dirk Trautmann, and Gerhard Baur,
+// Phys. Rev. A55 (1997) 396.
+// [2] K.Hencken, Yu.Kharlov, S.Sadovsky, Internal ALICE Note 2002-27.
+//%
+// Usage:
+// Initialization:
+// AliGenQEDBg *gener = new AliGenQEDBg();
+// gener->SetXXXRange(); // Set kinematics range
+// gener->SetLumiIntTime(double lumi, double sec); // luminosity and intergration time in seconds
+// gener->Init();
+// Event generation:
+// gener->Generate(); // Produce poissonian number of e+e- pair with average number
+// corresponding to requested integration time with given beam luminosity
+// Each pair has its own vertex, and time randomly distributed at originT
+// and originT+ integration time
+//
+// For details of generation see AliGenEpEmv1.cxx by Yuri.Kharlov@cern.ch
+
+#include "AliLog.h"
+#include "AliGenQEDBg.h"
+#include <TParticle.h>
+#include <TParticlePDG.h>
+#include <TDatabasePDG.h>
+#include <TEpEmGen.h>
+
+ClassImp(AliGenQEDBg)
+
+//------------------------------------------------------------
+
+AliGenQEDBg::AliGenQEDBg()
+: fLumi(0)
+ ,fXSection(0)
+ ,fXSectionEps(1e-2)
+ ,fIntTime(0)
+ ,fPairsInt(-1)
+ ,fMinXSTest(1e3)
+ ,fMaxXSTest(1e7)
+{
+}
+
+//____________________________________________________________
+AliGenQEDBg::~AliGenQEDBg()
+{
+ // Destructor
+}
+
+//____________________________________________________________
+void AliGenQEDBg::Init()
+{
+ // Initialisation:
+ AliInfo(Form("Will estimate QED bg. for L=%e cm^-2*s^-1 and Integration Time of %e s.",fLumi,fIntTime));
+ if (fLumi<=0 || fIntTime<=0) {
+ AliWarning("One of parameters is not set properly, no pairs will be generated");
+ return;
+ }
+ //
+ // initialize the generator of e+e- pair production
+ AliGenEpEmv1::Init();
+ //
+ fPairsInt = 0;
+ int ngen = 0;
+ AliInfo(Form("Estimating x-section with min.relative precision of %f and min/max test: %d/%d",
+ fXSectionEps,int(fMinXSTest),int(fMaxXSTest)));
+ //
+ double yElectron,yPositron,xElectron,xPositron,phi12,weight,err;
+ fXSection = -1;
+ do {
+ fEpEmGen->GenerateEvent(fYMin,fYMax,fPtMin,fPtMax,yElectron,yPositron,xElectron,xPositron,phi12,weight);
+ if (++ngen>fMinXSTest) { // ensure min number of tests
+ fXSection = fEpEmGen->GetXsection();
+ err = fEpEmGen->GetDsection();
+ }
+ } while(!((fXSection>0 && err/fXSection<fXSectionEps) || ngen>fMaxXSTest));
+ //
+ if (fXSection<=0) {
+ AliError(Form("X-section = %e after %d trials, cannot generate",fXSection,ngen));
+ return;
+ }
+ fPairsInt = fXSection*1e-21*fLumi*fIntTime; // xsestion is in kbarn!
+ AliInfo(Form("Estimated x-secion: %e+-%ekb in %d tests, <Npairs>=%e per %e time interval",
+ fXSection,err,ngen,fPairsInt,fIntTime));
+ //
+}
+
+//____________________________________________________________
+void AliGenQEDBg::Generate()
+{
+ //
+ // Generate poissian <fPairsInt> e+e- pairs, each one with its vertex
+ //
+ Float_t polar[3]= {0,0,0};
+ Float_t origin[3];
+ Float_t time = 0.;
+ Float_t p[3];
+ //
+ int npairs,nt,id;;
+ if (fPairsInt<=0 || (npairs=gRandom->Poisson(fPairsInt))<1) return;
+ //
+ Double_t ptElectron,ptPositron, phiElectron,phiPositron, mt, ms2 = fMass*fMass;
+ Double_t phi12=0,xElectron=0,xPositron=0,yElectron=0,yPositron=0,weight=0;
+ //
+ for (int i=0;i<npairs;i++) {
+ // each pair has its own vertex and time
+ Vertex();
+ for (int j=0;j<3;j++) origin[j] = fVertex[j];
+ time = fTimeOrigin+gRandom->Rndm()*fIntTime;
+ //
+ fEpEmGen->GenerateEvent(fYMin,fYMax,fPtMin,fPtMax,yElectron,yPositron,xElectron,xPositron,phi12,weight);
+ ptElectron = TMath::Power(10,xElectron) * 1.e-03;;
+ ptPositron = TMath::Power(10,xPositron) * 1.e-03;;
+ phiElectron = fPhiMin + gRandom->Rndm() * (fPhiMax-fPhiMin);
+ phiPositron = phiElectron + phi12;
+ // Produce electron
+ mt = TMath::Sqrt(ptElectron*ptElectron + ms2);
+ p[0] = ptElectron*TMath::Cos(phiElectron);
+ p[1] = ptElectron*TMath::Sin(phiElectron);
+ p[2] = mt*TMath::SinH(yElectron);
+ id = 11;
+ PushTrack(fTrackIt,-1, id,p,origin,polar,time,kPPrimary,nt,1);
+ //
+ // Produce positron
+ mt = TMath::Sqrt(ptPositron*ptPositron + ms2);
+ p[0] = ptPositron*TMath::Cos(phiPositron);
+ p[1] = ptPositron*TMath::Sin(phiPositron);
+ p[2] = mt*TMath::SinH(yPositron);
+ id = -11;
+ PushTrack(fTrackIt,-1, id,p,origin,polar,time,kPPrimary,nt,1);
+ //
+ }
+ fEvent++;
+ //
+ fHeader.SetNProduced(2*npairs);
+ fHeader.SetEventWeight(1);
+ fHeader.SetInteractionTime(fTimeOrigin);
+ AddHeader(&fHeader);
+}
+
+//__________________________________________________________
+void AliGenQEDBg::SetLumiIntTime(double lumi, double intTime)
+{
+ // assign luminosity and integration time
+ if (lumi<=0) AliFatal(Form("Luminosity must be positive, in cm^-2*s^-1, %e asked",lumi));
+ if (intTime<=0) AliFatal(Form("Integration time must be positive, in seconnds, %e asked",intTime));
+ fLumi = lumi;
+ fIntTime = intTime;
+ //
+}
+
+//__________________________________________________________
+void AliGenQEDBg::SetMinMaxXSTest(double mn,double mx)
+{
+ // set min,max number of generator calls for xsection estimates
+ fMinXSTest = mn>100 ? mn : 100.;
+ fMaxXSTest = mx>mx ? mx : mx+100.;
+}
--- /dev/null
+#ifndef ALIGENQEDBG_H
+#define ALIGENQEDBG_H
+/* Copyright(c) 1998-2002, ALICE Experiment at CERN, All rights reserved. *
+ * Copyright(c) 1997, 1998, 2002, Adrian Alscher and Kai Hencken *
+ * Copyright(c) 2002 Kai Hencken, Yuri Kharlov, Serguei Sadovsky *
+ * See cxx source for full Copyright notice */
+
+/* $Id$ */
+// Event generator of single e+e- pair production in ultraperipheral PbPb collisions
+// at 5.5 TeV/nucleon.
+// Author: Yuri.Kharlov@cern.ch
+// 9 October 2002
+
+#include "AliGenMC.h"
+#include "AliGenEventHeader.h"
+#include "AliGenEpEmv1.h"
+
+//-------------------------------------------------------------
+class AliGenQEDBg : public AliGenEpEmv1
+{
+public:
+ AliGenQEDBg();
+
+ virtual ~AliGenQEDBg();
+ virtual void Generate();
+ virtual void Init();
+ //
+ Double_t GetLuminosity() const {return fLumi;}
+ Double_t GetIntegrationTime() const {return fIntTime;}
+ Double_t GetXSection() const {return fXSection;}
+ Double_t GetXSectionEps() const {return fXSectionEps;}
+ Double_t GetMeanNPairs() const {return fPairsInt;}
+ //
+ void SetLumiIntTime(double lumi, double intTime);
+ void SetXSectionEps(double eps=1e-2) {fXSectionEps = eps>0 ? eps:1e-2;}
+ void SetMinMaxXSTest(double mn,double mx);
+ //
+ protected:
+ AliGenQEDBg(const AliGenQEDBg & gen);
+ AliGenQEDBg & operator=(const AliGenQEDBg & gen);
+ //
+ Double_t fLumi; // beam luminsity
+ Double_t fXSection; // estimated cross section in k-barns
+ Double_t fXSectionEps; // error with wich Xsection is calculated
+ Double_t fIntTime; // integration time in seconds
+ Double_t fPairsInt; // estimated average number of pairs in IntTime
+ Double_t fMinXSTest; // min number of generator calls for Xsection estimate
+ Double_t fMaxXSTest; // max number of generator calls for Xsection estimate
+
+ //
+ ClassDef(AliGenQEDBg,1) // Generator e+e- pair background from PbPb QED interactions
+};
+#endif
git://git.uio.no / u / mrichter / AliRoot.git / commitdiff