Rivet analyses
title: MC_DECAY_MESON_MESON_LEPTONS
MC analyis of $V\to P \ell^+\ell^-$ and $P\to V \ell^+\ell^-$ decays
Experiment: ()
Status: VALIDATED
Authors: - Peter Richardson
References: none listed
Beams: * *
Beam energies: ANY
Run details: - Any process producing vector or scalar meson decays
A Monte Carlo analysis for the decay of vector mesons to a pseudoscalar meson, or a pseudoscalar meson to a vector meson, and an $e^+e^-$ or $\mu^+\mu^-$ pair. All such decays are automatically identified. Based on old Herwig++ internal analysis.
Source code:MC_DECAY_MESON_MESON_LEPTONS.cc
```c++ // -- C++ --
include "Rivet/Analysis.hh"
include "Rivet/Projections/UnstableParticles.hh"
include "Rivet/Tools/ParticleIdUtils.hh"
namespace Rivet {
/// @brief MC decay M -> M l+ l- class MC_DECAY_MESON_MESON_LEPTONS : public Analysis { public:
/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(MC_DECAY_MESON_MESON_LEPTONS);
/// @name Analysis methods
/// @{
/// Book histograms and initialise projections before the run
void init() {
// Initialise and register projections
declare(UnstableParticles(), "UFS");
// book the Histos
// pi0 dalitz
bookHistos(111, 22, 11, 0.140);
// eta dalitz
bookHistos(221, 22, 11, 0.55);
bookHistos(221, 22, 13, 0.55);
// eta' dalitz
bookHistos(331, 22, 11, 0.96);
bookHistos(331, 22, 13, 0.96);
// omega -> pi0
bookHistos(223, 111, 11, 0.8);
bookHistos(223, 111, 13, 0.8);
// phi -> pi0
bookHistos(333, 111, 11, 1.1);
bookHistos(333, 111, 13, 1.1);
// phi -> eta
bookHistos(333, 221, 11, 1.1);
bookHistos(333, 221, 13, 1.1);
// J/psi dalitz
bookHistos(443, 22, 11, 3.1);
bookHistos(443, 22, 13, 3.1);
// B -> s gamma
bookHistos(511, 313, 11, 5.3);
bookHistos(511, 313, 13, 5.3);
}
void bookHistos(int id1, int id2, int il, double dM) {
if (abs(id2) % 10 == 3 || id2 == 22) {
_incoming_P.push_back(id1);
_outgoingV.push_back(id2);
_outgoingf_P.push_back(il);
std::ostringstream title;
title << "h2_" << abs(id1);
if (id1 > 0)
title << "p";
else
title << "m";
title << "_" << abs(id2);
if (id2 > 0)
title << "p";
else
title << "m";
title << "_" << il << "_";
_mff_P.push_back(Histo1DPtr());
book(_mff_P.back(), title.str() + "mff", 100, 0., dM);
_mVf.push_back(Histo1DPtr());
book(_mVf.back(), title.str() + "mVf", 100, 0., dM);
_mVfbar.push_back(Histo1DPtr());
book(_mVfbar.back(), title.str() + "mVfbar", 100, 0., dM);
}
else {
_incomingV.push_back(id1);
_outgoingP.push_back(id2);
_outgoingf_V.push_back(il);
std::ostringstream title;
title << "h_" << abs(id1);
if (id1 > 0)
title << "p";
else
title << "m";
title << "_" << abs(id2);
if (id2 > 0)
title << "p";
else
title << "m";
title << "_" << il << "_";
_mff_V.push_back(Histo1DPtr());
book(_mff_V.back(), title.str() + "mff", 100, 0., dM);
_mPf.push_back(Histo1DPtr());
book(_mPf.back(), title.str() + "mPf", 100, 0., dM);
_mPfbar.push_back(Histo1DPtr());
book(_mPfbar.back(), title.str() + "mPfbar", 100, 0., dM);
}
}
void findDecayProducts(const Particle& mother,
unsigned int& nstable,
Particles& lp,
Particles& lm,
Particles& scalar,
Particles& vector) {
for (const Particle& p : mother.children()) {
int id = p.pid();
if (id == PID::EMINUS || id == PID::MUON) {
lm.push_back(p);
++nstable;
}
else if (id == PID::EPLUS || id == PID::ANTIMUON) {
lp.push_back(p);
++nstable;
}
else if (abs(id) % 10 == 1 && PID::isMeson(id)) {
scalar.push_back(p);
++nstable;
}
else if ((abs(id) % 10 == 3 && PID::isMeson(id)) || id == PID::PHOTON) {
vector.push_back(p);
++nstable;
}
else if (!p.children().empty()) {
findDecayProducts(p, nstable, lp, lm, scalar, vector);
}
else
++nstable;
}
}
/// Perform the per-event analysis
void analyze(const Event& event) {
// loop over unstable particles
for (const Particle& iMeson : apply<UnstableParticles>(event, "UFS").particles()) {
// only consider scalar/vector mesons
long pid = iMeson.pid();
if (!PID::isMeson(pid)) continue;
if (abs(pid) % 10 != 3 and abs(pid) % 10 != 1) continue;
Particles lp, lm, scalar, vector;
unsigned int nstable(0);
findDecayProducts(iMeson, nstable, lp, lm, scalar, vector);
if (nstable != 3 || lp.size() != 1 || lm.size() != 1 || lp[0].pid() != -lm[0].pid()) continue;
if (scalar.size() == 1) {
// check if we already have this decay
unsigned int ix = 0;
bool found(false);
while (!found && ix < _incomingV.size()) {
if (_incomingV[ix] == pid && _outgoingP[ix] == scalar[0].pid()
&& _outgoingf_V[ix] == lm[0].pid()) {
found = true;
}
else {
++ix;
}
}
// create a new graph if needed
if (!found) {
MSG_WARNING("MC_DECAY_MESON_MESON_LEPTONS S" << iMeson.pid() << " " << scalar[0].pid() << " "
<< iMeson.mass() << "\n");
continue;
}
// add the results to the histogram
_mff_V[ix]->fill((lm[0].momentum() + lp[0].momentum()).mass());
_mPf[ix]->fill((scalar[0].momentum() + lm[0].momentum()).mass());
_mPfbar[ix]->fill((scalar[0].momentum() + lp[0].momentum()).mass());
}
else if (vector.size() == 1) {
// check if we already have this decay
unsigned int ix = 0;
bool found(false);
while (!found && ix < _incoming_P.size()) {
if (_incoming_P[ix] == pid && _outgoingV[ix] == vector[0].pid()
&& _outgoingf_P[ix] == lm[0].pid()) {
found = true;
}
else {
++ix;
}
}
// create a new graph if needed
if (!found) {
MSG_WARNING("MC_DECAY_MESON_MESON_LEPTONS V" << iMeson.pid() << " " << vector[0].pid() << " "
<< iMeson.mass() << "\n");
continue;
}
// add the results to the histogram
_mff_P[ix]->fill((lm[0].momentum() + lp[0].momentum()).mass());
_mVf[ix]->fill((vector[0].momentum() + lm[0].momentum()).mass());
_mVfbar[ix]->fill((vector[0].momentum() + lp[0].momentum()).mass());
}
}
}
/// Normalise histograms etc., after the run
void finalize() {
// normalize to unity V->P
for (unsigned int ix = 0; ix < _mff_V.size(); ++ix) {
normalize(_mff_V);
normalize(_mPf);
normalize(_mPfbar);
}
// normalize to unity P->V
for (unsigned int ix = 0; ix < _mff_P.size(); ++ix) {
normalize(_mff_P);
normalize(_mVf);
normalize(_mVfbar);
}
}
/// @}
/// @name Histograms for V -> P
/// @{
/**
* PDG codes of the incoming particles
*/
vector<long> _incomingV;
/**
* PDG codes of the outgoing pseudoscalar mesons
*/
vector<long> _outgoingP;
/**
* PDG codes of the outgoing fermion
*/
vector<long> _outgoingf_V;
/**
* Histograms for the mass of the fermion-antifermion pair
*/
vector<Histo1DPtr> _mff_V;
/**
* Histograms for the masses of the pseudoscalar and the fermion
*/
vector<Histo1DPtr> _mPf;
/**
* Histograms for the masses of the pseudoscalar and the antifermion
*/
vector<Histo1DPtr> _mPfbar;
/// @}
/// @name Histograms P->V
/// @{
/**
* PDG codes of the incoming_P particles
*/
vector<long> _incoming_P;
/**
* PDG codes of the outgoing vector mesons
*/
vector<long> _outgoingV;
/**
* PDG codes of the outgoing fermion
*/
vector<long> _outgoingf_P;
/**
* Histograms for the mass of the fermion-antifermion pair
*/
vector<Histo1DPtr> _mff_P;
/**
* Histograms for the masses of the vector and the fermion
*/
vector<Histo1DPtr> _mVf;
/**
* Histograms for the masses of the vector and the antifermion
*/
vector<Histo1DPtr> _mVfbar;
/// @}
};
RIVET_DECLARE_PLUGIN(MC_DECAY_MESON_MESON_LEPTONS);
} ```