--- /dev/null
+/**************************************************************************
+ * Copyright(c) 1998-1999, 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. *
+ **************************************************************************/
+
+/*
+$Log$
+*/
+
+/*
+ Generator for gray nucluons in pA interactions.
+ Source is modelled by a relativistic Maxwell distributions.
+ Original code by Ferenc Sikler <sikler@rmki.kfki.hu>
+ */
+#include "AliGenGrayParticles.h"
+#include "AliPDG.h"
+#include <TDatabasePDG.h>
+
+ ClassImp(AliGenGrayParticles)
+
+ AliGenGrayParticles::AliGenGrayParticles():AliGenerator(-1)
+{
+// Default constructor
+}
+
+AliGenGrayParticles::AliGenGrayParticles(Int_t npart)
+ :AliGenerator(npart)
+{
+// Constructor
+ fName = "GrayParticles";
+ fTitle = "Generator for gray particles in pA collisions";
+ SetPmax();
+ SetTarget();
+ SetNominalCmsEnergy();
+ SetTemperature();
+}
+
+//____________________________________________________________
+AliGenGrayParticles::~AliGenGrayParticles()
+{
+// Destructor
+}
+
+
+void AliGenGrayParticles::Init()
+{
+ //
+ // Initialization
+ //
+ Float_t kMass = TDatabasePDG::Instance()->GetParticle(kProton)->Mass();
+ fMomentum = fCMS/2. * fZTarget / fATarget;
+ fBeta = fMomentum / TMath::Sqrt(kMass * kMass + fMomentum * fMomentum);
+}
+
+
+void AliGenGrayParticles::Generate()
+{
+ //
+ // Generate one event
+ //
+ Float_t p[3];
+ Float_t origin[3] = {0., 0., 0.};
+ Float_t polar [3] = {0., 0., 0.};
+ Int_t nt, i;
+ for(i = 0;i < fNpart; i++) {
+ Int_t kf = kProton;
+ GenerateSlow(1, fTemperature, 0., p);
+
+ SetTrack(fTrackIt, -1, kf, p, origin, polar,
+ 0., kPNoProcess, nt, 1.);
+
+ KeepTrack(nt);
+ }
+}
+
+
+
+
+void AliGenGrayParticles::GenerateSlow(Int_t charge, Double_t T, Double_t beta, Float_t* q)
+/*
+ Emit a slow nucleon with "temperature" T [GeV],
+ from a source moving with velocity beta
+ Three-momentum [GeV/c] is given back in q[3]
+*/
+
+{
+ Double_t m, pmax, p, f, theta, phi;
+
+ TDatabasePDG * pdg = TDatabasePDG::Instance();
+ const Double_t kMassProton = pdg->GetParticle(kProton) ->Mass();
+ const Double_t kMassNeutron = pdg->GetParticle(kNeutron)->Mass();
+
+ /* Select nucleon type */
+ if(charge == 0) m = kMassNeutron;
+ else m = kMassProton;
+
+ /* Momentum at maximum of Maxwell-distribution */
+
+ pmax = TMath::Sqrt(2*T*(T+sqrt(T*T+m*m)));
+
+ /* Try until proper momentum */
+ /* for lack of primitive function of the Maxwell-distribution */
+ /* a brute force trial-accept loop, normalized at pmax */
+
+ do
+ {
+ p = Rndm() * fPmax;
+ f = Maxwell(m, p, T) / Maxwell(m , pmax, T);
+ }
+ while(f < Rndm());
+
+ /* Spherical symmetric emission */
+ theta = TMath::ACos(2. * Rndm() - 1.);
+ phi = 2. * TMath::Pi() * Rndm();
+
+ /* Determine momentum components in system of the moving source */
+ q[0] = p * TMath::Sin(theta) * TMath::Cos(phi);
+ q[1] = p * TMath::Sin(theta) * TMath::Sin(phi);
+ q[2] = p * TMath::Cos(theta);
+
+ /* Transform to system of the target nucleus */
+ /* beta is passed as negative, because the gray nucleons are slowed down */
+ Lorentz(m, -beta, q);
+
+ /* Transform to laboratory system */
+ Lorentz(m, fBeta, q);
+}
+
+Double_t AliGenGrayParticles::Maxwell(Double_t m, Double_t p, Double_t T)
+{
+/* Relativistic Maxwell-distribution */
+ Double_t ekin;
+ ekin = TMath::Sqrt(p*p+m*m)-m;
+ return (p*p * exp(-ekin/T));
+}
+
+
+void AliGenGrayParticles::Lorentz(Double_t m, Double_t beta, Float_t* q)
+{
+/* Lorentz transform in the direction of q[2] */
+
+ Double_t gamma = 1/sqrt(1-beta*beta);
+ Double_t energy = sqrt(m*m + q[0]*q[0] + q[1]*q[1] + q[2]*q[2]);
+ q[2] = gamma * (q[2] + beta*energy);
+}
+
+
+
+
+
+
+
--- /dev/null
+#ifndef ALIGENGRAYPARTICLES_H
+#define ALIGENGRAYPARTICLES_H
+/* Copyright(c) 198-1999, ALICE Experiment at CERN, All rights reserved. *
+ * See cxx source for full Copyright notice */
+
+/* $Id$ */
+
+#include "AliGenerator.h"
+
+class AliGenGrayParticles : public AliGenerator
+{
+public:
+ AliGenGrayParticles();
+ AliGenGrayParticles(Int_t npart);
+ virtual ~AliGenGrayParticles();
+ virtual void Init();
+ virtual void Generate();
+ virtual void SetPmax(Float_t pmax = 10.) {fPmax = pmax;}
+ virtual void SetNominalCmsEnergy(Float_t energy = 14000.) {fCMS = energy;}
+ virtual void SetTarget(Float_t a=208, Float_t z=82) {fATarget = a; fZTarget = z;}
+ virtual void SetTemperature(Double_t t = 0.05) {fTemperature = t;}
+
+ protected:
+ void GenerateSlow(Int_t charge, Double_t T, Double_t beta, Float_t* q);
+ Double_t Maxwell(Double_t m, Double_t p, Double_t t);
+ void Lorentz(Double_t m, Double_t beta, Float_t* q);
+ protected:
+ Float_t fCMS; // Center of mass energy
+ Float_t fMomentum; // Target nucleus momentum
+ Float_t fBeta; // Target nucleus beta
+ Float_t fPmax; // Maximum slow nucleon momentum
+ Float_t fATarget; // Target nucleus mass number
+ Float_t fZTarget; // Target nucleus charge number
+ Float_t fTemperature; // Source Temperature
+ ClassDef(AliGenGrayParticles,1) // Gray Particle Generator
+};
+#endif
+
+
+
+
+
+
git://git.uio.no / u / mrichter / AliRoot.git / commitdiff