| Geant4 Cross Reference |
1 // 1
2 // *******************************************
3 // * License and Disclaimer
4 // *
5 // * The Geant4 software is copyright of th
6 // * the Geant4 Collaboration. It is provided
7 // * conditions of the Geant4 Software License
8 // * LICENSE and available at http://cern.ch/
9 // * include a list of copyright holders.
10 // *
11 // * Neither the authors of this software syst
12 // * institutes,nor the agencies providing fin
13 // * work make any representation or warran
14 // * regarding this software system or assum
15 // * use. Please see the license in the file
16 // * for the full disclaimer and the limitatio
17 // *
18 // * This code implementation is the result
19 // * technical work of the GEANT4 collaboratio
20 // * By using, copying, modifying or distri
21 // * any work based on the software) you ag
22 // * use in resulting scientific publicati
23 // * acceptance of all terms of the Geant4 Sof
24 // *******************************************
25 //
26 //
27 // Multibody "phase space" generator using Kop
28 //
29 // Author: Michael Kelsey (SLAC) <kelsey@slac
30
31 #include "G4HadPhaseSpaceKopylov.hh"
32 #include "G4LorentzVector.hh"
33 #include "G4Pow.hh"
34 #include "Randomize.hh"
35 #include <vector>
36 #include <algorithm>
37 #include <numeric>
38 #include <cmath>
39
40
41 // Generator
42
43 void G4HadPhaseSpaceKopylov::
44 GenerateMultiBody(G4double initialMass,
45 const std::vector<G4double>& masses,
46 std::vector<G4LorentzVector>& finalState
47 if (GetVerboseLevel()) G4cout << GetName() <
48
49 finalState.clear();
50
51 G4int N = (G4int)masses.size();
52 finalState.resize(N);
53
54 G4double mtot = std::accumulate(masses.begin
55 G4double mu = mtot;
56 G4double PFragMagCM = 0.0;
57 G4double Mass = initialMass;
58 G4double T = Mass-mtot;
59 G4LorentzVector PFragCM(0.0,0.0,0.0,0.0);
60 G4LorentzVector PRestCM(0.0,0.0,0.0,0.0);
61 G4LorentzVector PRestLab(0.0,0.0,0.0,Mass);
62
63 for (G4int k=N-1; k>0; --k) {
64 mu -= masses[k];
65 T *= (k>1) ? BetaKopylov(k) : 0.;
66
67 G4double RestMass = mu + T;
68
69 PFragMagCM = TwoBodyMomentum(Mass,masses[k
70
71 // Create a unit vector with a random dire
72 G4ThreeVector RandVector = UniformVector(P
73
74 PFragCM.setVectM(RandVector,masses[k]);
75 PRestCM.setVectM(-RandVector,RestMass);
76
77 G4ThreeVector BoostV = PRestLab.boostVecto
78
79 PFragCM.boost(BoostV);
80 PRestCM.boost(BoostV);
81 PRestLab = PRestCM;
82 Mass = RestMass;
83 finalState[k] = PFragCM;
84 }
85
86 finalState[0] = PRestLab;
87 }
88
89
90 // Generate scale factor for final state parti
91
92 G4double G4HadPhaseSpaceKopylov::BetaKopylov(G
93 G4Pow* g4pow = G4Pow::GetInstance();
94
95 G4int N = 3*K - 5;
96 G4double xN = G4double(N);
97 G4double Fmax = std::sqrt(g4pow->powN(xN/(xN
98
99 G4double F, chi;
100 const G4int maxNumberOfLoops = 10000;
101 G4int loopCounter = 0;
102 do {
103 chi = G4UniformRand();
104 F = std::sqrt(g4pow->powN(chi,N)*(1.-chi))
105 } while ( ( Fmax*G4UniformRand() > F ) && ++
106 if ( loopCounter >= maxNumberOfLoops ) {
107 G4ExceptionDescription ed;
108 ed << " Failed sampling after maxNumberOfL
109 G4Exception( " G4HadPhaseSpaceKopylov::Bet
110 }
111
112 return chi;
113 }
114