|
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
|
#include "FastSimulation/ParticlePropagator/interface/ParticlePropagator.h"
#include "FastSimulation/Particle/interface/makeParticle.h"
#include "FastSimulation/ParticleDecay/interface/PythiaDecays.h"
#include "FWCore/ServiceRegistry/interface/RandomEngineSentry.h"
#include <Pythia8/Pythia.h>
#include <memory>
#include "Pythia8Plugins/HepMC2.h"
PythiaDecays::PythiaDecays() {
// inspired by method Pythia8Hadronizer::residualDecay() in GeneratorInterface/Pythia8Interface/src/Py8GunBase.cc
decayer = std::make_unique<Pythia8::Pythia>();
p8RndmEngine = std::make_shared<gen::P8RndmEngine>();
decayer->setRndmEnginePtr(p8RndmEngine);
decayer->settings.flag("ProcessLevel:all", false);
decayer->settings.flag("PartonLevel:FSRinResonances", false);
decayer->settings.flag("ProcessLevel:resonanceDecays", false);
decayer->init();
// forbid all decays
// (decays are allowed selectively in the particleDaughters function)
Pythia8::ParticleData& pdt = decayer->particleData;
int pid = 1;
while (pdt.nextId(pid) > pid) {
pid = pdt.nextId(pid);
pdt.mayDecay(pid, false);
}
}
PythiaDecays::~PythiaDecays() {}
const DaughterParticleList& PythiaDecays::particleDaughters(ParticlePropagator& particle,
CLHEP::HepRandomEngine* engine) {
edm::RandomEngineSentry<gen::P8RndmEngine> sentry(p8RndmEngine.get(), engine);
theList.clear();
// inspired by method Pythia8Hadronizer::residualDecay() in GeneratorInterface/Pythia8Interface/src/Py8GunBase.cc
int pid = particle.particle().pid();
decayer->event.reset();
Pythia8::Particle py8part(pid,
93,
0,
0,
0,
0,
0,
0,
particle.particle().momentum().x(), // note: momentum().x() and Px() are the same
particle.particle().momentum().y(),
particle.particle().momentum().z(),
particle.particle().momentum().t(),
particle.particle().mass());
py8part.vProd(particle.particle().X(), particle.particle().Y(), particle.particle().Z(), particle.particle().T());
decayer->event.append(py8part);
int nentries_before = decayer->event.size();
decayer->particleData.mayDecay(pid,
true); // switch on the decay of this and only this particle (avoid double decays)
decayer->next(); // do the decay
decayer->particleData.mayDecay(pid, false); // switch it off again
int nentries_after = decayer->event.size();
if (nentries_after <= nentries_before)
return theList;
theList.reserve(nentries_after - nentries_before);
for (int ipart = nentries_before; ipart < nentries_after; ipart++) {
Pythia8::Particle& py8daughter = decayer->event[ipart];
theList
.emplace_back(makeParticle(
particle.particleDataTable(),
py8daughter.id(),
XYZTLorentzVector(py8daughter.px(), py8daughter.py(), py8daughter.pz(), py8daughter.e()),
XYZTLorentzVector(py8daughter.xProd(), py8daughter.yProd(), py8daughter.zProd(), py8daughter.tProd())))
.setMass(py8daughter.m());
}
return theList;
}
|