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0ca57c2f | 1 | //-------------------------------------------------------------------------- |
2 | // | |
3 | // Environment: | |
4 | // This software is part of the EvtGen package developed jointly | |
5 | // for the BaBar and CLEO collaborations. If you use all or part | |
6 | // of it, please give an appropriate acknowledgement. | |
7 | // | |
8 | // Copyright Information: See EvtGen/COPYRIGHT | |
9 | // Copyright (C) 1998 Caltech, UCSB | |
10 | // 2011 University of Warwick, UK | |
11 | // Module: EvtPythia.cc | |
12 | // | |
13 | // Description: Routine to decay a particle according th phase space | |
14 | // | |
15 | // Modification history: | |
16 | // | |
17 | // RYD January 8, 1997 Module created | |
18 | // JJB April 2011 Modified to use new Pythia8 interface | |
19 | // | |
20 | //------------------------------------------------------------------------ | |
21 | ||
22 | #include "EvtGenBase/EvtPatches.hh" | |
23 | ||
24 | #include "EvtGenBase/EvtParticle.hh" | |
25 | #include "EvtGenBase/EvtId.hh" | |
26 | #include "EvtGenBase/EvtPDL.hh" | |
27 | #include "EvtGenBase/EvtSpinDensity.hh" | |
28 | ||
29 | #include "EvtGenExternal/EvtPythia.hh" | |
30 | ||
31 | #include "EvtGenExternal/EvtExternalGenFactory.hh" | |
32 | #include "EvtGenModels/EvtAbsExternalGen.hh" | |
33 | #include "EvtGenBase/EvtDecayBase.hh" | |
34 | ||
35 | #include <iostream> | |
36 | #include <cmath> | |
37 | ||
38 | EvtPythia::EvtPythia() { | |
39 | ||
40 | // Set the Pythia engine to a null pointer at first. | |
41 | // When we do the decay, we retrieve the pointer to the Pythia engine | |
42 | // and use that for all decays. All clones will use the same Pythia engine. | |
43 | _pythiaEngine = 0; | |
44 | ||
45 | } | |
46 | ||
47 | EvtPythia::~EvtPythia() { | |
48 | _commandList.clear(); | |
49 | } | |
50 | ||
51 | std::string EvtPythia::getName(){ | |
52 | ||
53 | return "PYTHIA"; | |
54 | ||
55 | } | |
56 | ||
57 | EvtDecayBase* EvtPythia::clone(){ | |
58 | ||
59 | return new EvtPythia(); | |
60 | ||
61 | } | |
62 | ||
63 | ||
64 | void EvtPythia::init(){ | |
65 | ||
66 | // Do not check for any arguments. The PythiaEngine will check | |
67 | // to see if there is an integer specifying the decay physics, | |
68 | // otherwise it just uses phase-space. | |
69 | ||
70 | } | |
71 | ||
72 | void EvtPythia::initProbMax(){ | |
73 | ||
74 | noProbMax(); | |
75 | ||
76 | } | |
77 | ||
78 | void EvtPythia::decay( EvtParticle *p ){ | |
79 | ||
80 | // We have to initialise the Pythia engine after the decay.dec files have been read in, | |
81 | // since we will be modifying Pythia data tables, and that is only possible once we have | |
82 | // defined all Pythia-type decays we want to use. | |
83 | // We check to see if the engine has been created before doing the decay. | |
84 | // This should only create the full Pythia engine once, and all clones will point to the same engine. | |
85 | ||
86 | if (_pythiaEngine == 0) { | |
87 | _pythiaEngine = EvtExternalGenFactory::getInstance()->getGenerator(EvtExternalGenFactory::PythiaGenId); | |
88 | } | |
89 | ||
90 | if (_pythiaEngine != 0) { | |
91 | _pythiaEngine->doDecay(p); | |
92 | } | |
93 | ||
94 | this->fixPolarisations(p); | |
95 | ||
96 | } | |
97 | ||
98 | void EvtPythia::fixPolarisations(EvtParticle *p) { | |
99 | ||
100 | // Special case to handle the J/psi polarisation | |
101 | ||
102 | if (p == 0) {return;} | |
103 | ||
104 | int nDaug = p->getNDaug(); | |
105 | int i(0); | |
106 | ||
107 | static EvtId Jpsi = EvtPDL::getId("J/psi"); | |
108 | ||
109 | for (i = 0; i < nDaug; i++){ | |
110 | ||
111 | EvtParticle* theDaug = p->getDaug(i); | |
112 | ||
113 | if (theDaug != 0) { | |
114 | ||
115 | if (theDaug->getId() == Jpsi) { | |
116 | ||
117 | EvtSpinDensity rho; | |
118 | ||
119 | rho.setDim(3); | |
120 | rho.set(0,0,0.5); | |
121 | rho.set(0,1,0.0); | |
122 | rho.set(0,2,0.0); | |
123 | ||
124 | rho.set(1,0,0.0); | |
125 | rho.set(1,1,1.0); | |
126 | rho.set(1,2,0.0); | |
127 | ||
128 | rho.set(2,0,0.0); | |
129 | rho.set(2,1,0.0); | |
130 | rho.set(2,2,0.5); | |
131 | ||
132 | EvtVector4R p4Psi = theDaug->getP4(); | |
133 | ||
134 | double alpha = atan2(p4Psi.get(2),p4Psi.get(1)); | |
135 | double beta = acos(p4Psi.get(3)/p4Psi.d3mag()); | |
136 | ||
137 | theDaug->setSpinDensityForwardHelicityBasis(rho,alpha,beta,0.0); | |
138 | setDaughterSpinDensity(i); | |
139 | ||
140 | } | |
141 | } | |
142 | } | |
143 | } | |
144 | ||
145 | std::string EvtPythia::commandName() { | |
146 | ||
147 | // Allow backward compatibility for decay.dec files | |
148 | // having JetSetPar parameters. They are obsolete for Pythia 8, | |
149 | // since the JetSet-type array variables do not exist. | |
150 | // Need to think about including user defined parameters in | |
151 | // EvtPythiaEngine::updatePhysicsParameters(). | |
152 | return std::string("JetSetPar"); | |
153 | ||
154 | } | |
155 | ||
156 | void EvtPythia::command(std::string cmd) { | |
157 | ||
158 | // Locally store commands in a vector | |
159 | _commandList.push_back(cmd); | |
160 | ||
161 | } |