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 1.1.2.1 2002/10/10 16:40:08 hristov
19 Updating VirtualMC to v3-09-02
21 Revision 1.1 2002/10/08 13:53:17 morsch
22 Gray particle generator, first commit.
27 Generator for gray nucluons in pA interactions.
28 Source is modelled by a relativistic Maxwell distributions.
29 Original code by Ferenc Sikler <sikler@rmki.kfki.hu>
31 #include "AliGenGrayParticles.h"
33 #include <TDatabasePDG.h>
35 ClassImp(AliGenGrayParticles)
37 AliGenGrayParticles::AliGenGrayParticles():AliGenerator(-1)
39 // Default constructor
42 AliGenGrayParticles::AliGenGrayParticles(Int_t npart)
46 fName = "GrayParticles";
47 fTitle = "Generator for gray particles in pA collisions";
50 SetNominalCmsEnergy();
54 //____________________________________________________________
55 AliGenGrayParticles::~AliGenGrayParticles()
61 void AliGenGrayParticles::Init()
66 Float_t kMass = TDatabasePDG::Instance()->GetParticle(kProton)->Mass();
67 fMomentum = fCMS/2. * fZTarget / fATarget;
68 fBeta = fMomentum / TMath::Sqrt(kMass * kMass + fMomentum * fMomentum);
72 void AliGenGrayParticles::Generate()
78 Float_t origin[3] = {0., 0., 0.};
79 Float_t polar [3] = {0., 0., 0.};
81 for(i = 0;i < fNpart; i++) {
83 GenerateSlow(1, fTemperature, 0., p);
85 SetTrack(fTrackIt, -1, kf, p, origin, polar,
86 0., kPNoProcess, nt, 1.);
95 void AliGenGrayParticles::GenerateSlow(Int_t charge, Double_t T, Double_t beta, Float_t* q)
97 Emit a slow nucleon with "temperature" T [GeV],
98 from a source moving with velocity beta
99 Three-momentum [GeV/c] is given back in q[3]
103 Double_t m, pmax, p, f, theta, phi;
105 TDatabasePDG * pdg = TDatabasePDG::Instance();
106 const Double_t kMassProton = pdg->GetParticle(kProton) ->Mass();
107 const Double_t kMassNeutron = pdg->GetParticle(kNeutron)->Mass();
109 /* Select nucleon type */
110 if(charge == 0) m = kMassNeutron;
111 else m = kMassProton;
113 /* Momentum at maximum of Maxwell-distribution */
115 pmax = TMath::Sqrt(2*T*(T+sqrt(T*T+m*m)));
117 /* Try until proper momentum */
118 /* for lack of primitive function of the Maxwell-distribution */
119 /* a brute force trial-accept loop, normalized at pmax */
124 f = Maxwell(m, p, T) / Maxwell(m , pmax, T);
128 /* Spherical symmetric emission */
129 theta = TMath::ACos(2. * Rndm() - 1.);
130 phi = 2. * TMath::Pi() * Rndm();
132 /* Determine momentum components in system of the moving source */
133 q[0] = p * TMath::Sin(theta) * TMath::Cos(phi);
134 q[1] = p * TMath::Sin(theta) * TMath::Sin(phi);
135 q[2] = p * TMath::Cos(theta);
137 /* Transform to system of the target nucleus */
138 /* beta is passed as negative, because the gray nucleons are slowed down */
139 Lorentz(m, -beta, q);
141 /* Transform to laboratory system */
142 Lorentz(m, fBeta, q);
145 Double_t AliGenGrayParticles::Maxwell(Double_t m, Double_t p, Double_t T)
147 /* Relativistic Maxwell-distribution */
149 ekin = TMath::Sqrt(p*p+m*m)-m;
150 return (p*p * exp(-ekin/T));
154 void AliGenGrayParticles::Lorentz(Double_t m, Double_t beta, Float_t* q)
156 /* Lorentz transform in the direction of q[2] */
158 Double_t gamma = 1/sqrt(1-beta*beta);
159 Double_t energy = sqrt(m*m + q[0]*q[0] + q[1]*q[1] + q[2]*q[2]);
160 q[2] = gamma * (q[2] + beta*energy);