1 /**************************************************************************
2 * Copyright(c) 1998-1999, 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. *
14 **************************************************************************/
18 Revision 1.2 2002/10/14 14:55:35 hristov
19 Merging the VirtualMC branch to the main development branch (HEAD)
21 Revision 1.1.2.1 2002/10/10 16:40:08 hristov
22 Updating VirtualMC to v3-09-02
24 Revision 1.1 2002/10/08 13:53:17 morsch
25 Gray particle generator, first commit.
30 Generator for gray nucluons in pA interactions.
31 Source is modelled by a relativistic Maxwell distributions.
32 Original code by Ferenc Sikler <sikler@rmki.kfki.hu>
34 #include "AliGenGrayParticles.h"
36 #include <TDatabasePDG.h>
38 ClassImp(AliGenGrayParticles)
40 AliGenGrayParticles::AliGenGrayParticles():AliGenerator(-1)
42 // Default constructor
45 AliGenGrayParticles::AliGenGrayParticles(Int_t npart)
49 fName = "GrayParticles";
50 fTitle = "Generator for gray particles in pA collisions";
53 SetNominalCmsEnergy();
59 //____________________________________________________________
60 AliGenGrayParticles::~AliGenGrayParticles()
66 void AliGenGrayParticles::Init()
71 Float_t kMass = TDatabasePDG::Instance()->GetParticle(kProton)->Mass();
72 fMomentum = fCMS/2. * fZTarget / fATarget;
73 fBeta = fMomentum / TMath::Sqrt(kMass * kMass + fMomentum * fMomentum);
77 void AliGenGrayParticles::Generate()
83 Float_t origin[3] = {0., 0., 0.};
84 Float_t polar [3] = {0., 0., 0.};
86 for(i = 0;i < fNpart; i++) {
88 if(fCharge==1) kf = kProton;
90 GenerateSlow(fCharge, fTemperature, fBetaSource, p);
92 SetTrack(fTrackIt, -1, kf, p, origin, polar,
93 0., kPNoProcess, nt, 1.);
102 void AliGenGrayParticles::GenerateSlow(Int_t charge, Double_t T, Double_t beta, Float_t* q)
104 Emit a slow nucleon with "temperature" T [GeV],
105 from a source moving with velocity beta
106 Three-momentum [GeV/c] is given back in q[3]
110 Double_t m, pmax, p, f, theta, phi;
112 TDatabasePDG * pdg = TDatabasePDG::Instance();
113 const Double_t kMassProton = pdg->GetParticle(kProton) ->Mass();
114 const Double_t kMassNeutron = pdg->GetParticle(kNeutron)->Mass();
116 /* Select nucleon type */
117 if(charge == 0) m = kMassNeutron;
118 else m = kMassProton;
120 /* Momentum at maximum of Maxwell-distribution */
122 pmax = TMath::Sqrt(2*T*(T+sqrt(T*T+m*m)));
124 /* Try until proper momentum */
125 /* for lack of primitive function of the Maxwell-distribution */
126 /* a brute force trial-accept loop, normalized at pmax */
131 f = Maxwell(m, p, T) / Maxwell(m , pmax, T);
135 /* Spherical symmetric emission */
136 theta = TMath::ACos(2. * Rndm() - 1.);
137 phi = 2. * TMath::Pi() * Rndm();
139 /* Determine momentum components in system of the moving source */
140 q[0] = p * TMath::Sin(theta) * TMath::Cos(phi);
141 q[1] = p * TMath::Sin(theta) * TMath::Sin(phi);
142 q[2] = p * TMath::Cos(theta);
144 /* Transform to system of the target nucleus */
145 /* beta is passed as negative, because the gray nucleons are slowed down */
146 Lorentz(m, -beta, q);
148 /* Transform to laboratory system */
149 Lorentz(m, fBeta, q);
152 Double_t AliGenGrayParticles::Maxwell(Double_t m, Double_t p, Double_t T)
154 /* Relativistic Maxwell-distribution */
156 ekin = TMath::Sqrt(p*p+m*m)-m;
157 return (p*p * exp(-ekin/T));
161 void AliGenGrayParticles::Lorentz(Double_t m, Double_t beta, Float_t* q)
163 /* Lorentz transform in the direction of q[2] */
165 Double_t gamma = 1/sqrt(1-beta*beta);
166 Double_t energy = sqrt(m*m + q[0]*q[0] + q[1]*q[1] + q[2]*q[2]);
167 q[2] = gamma * (q[2] + beta*energy);