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| // -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/UnstableParticles.hh"
namespace Rivet {
/// @brief Add a short analysis description here
class MC_Onium_PiPi_Decay : public Analysis {
public:
/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(MC_Onium_PiPi_Decay);
/// @name Analysis methods
//@{
/// Book histograms and initialise projections before the run
void init() {
// Initialise and register projections
declare(UnstableParticles(),"UFS");
// psi 2S
bookHistos(100443, 443,0.6);
// psi(3770)
bookHistos( 30443, 443,0.7);
// Upsilon (4S)
bookHistos(300553, 553,1.2);
bookHistos(300553,100553,0.6);
// Upsilon (3S)
bookHistos(200553, 553,0.9);
bookHistos(200553,100553,0.4);
// Upsilon (2S)
bookHistos(100553, 553,0.6);
}
void bookHistos(int id1, int id2, double deltaM) {
double twompi = 0.378;
_incoming.push_back(id1);
_outgoing.push_back(id2);
std::ostringstream title;
title << "h_" << id1 << "_" << id2 << "_";
_mpipi.push_back(make_pair(Histo1DPtr(), Histo1DPtr()));
book(_mpipi.back().first, title.str()+"mpippim",100,twompi/GeV,deltaM/GeV);
book(_mpipi.back().second, title.str()+"mpi0pi0",100,twompi/GeV,deltaM/GeV);
_hel.push_back(make_pair(Histo1DPtr(), Histo1DPtr()));
book(_hel.back().first, title.str()+"hpippim",100,-1.,1.);
book(_hel.back().second, title.str()+"hpi0pi0",100, 0.,1.);
}
void findDecayProducts(const Particle & mother,
unsigned int & nstable,
Particles& pip, Particles& pim,
Particles& pi0, Particles & onium) {
for(const Particle & p : mother.children()) {
int id = p.pid();
if ( id == PID::PIMINUS) {
pim.push_back(p);
++nstable;
}
else if (id == PID::PIPLUS) {
pip.push_back(p);
++nstable;
}
else if (id == PID::PI0) {
pi0.push_back(p);
++nstable;
}
else if (abs(id)%1000==443 || abs(id)%1000==553) {
onium.push_back(p);
++nstable;
}
else if ( !p.children().empty() ) {
findDecayProducts(p,nstable,pip,pim,pi0,onium);
}
else
++nstable;
}
}
/// Perform the per-event analysis
void analyze(const Event& event) {
// loop over unstable particles
for(const Particle& vMeson : apply<UnstableParticles>(event, "UFS").particles()) {
int id = vMeson.pid();
if(id%1000!=443 && id%1000!=553) continue;
unsigned int nstable(0);
Particles pip, pim, pi0, onium;
findDecayProducts(vMeson,nstable,pip,pim,pi0,onium);
// check for onium
if(onium.size() !=1 || nstable !=3) continue;
// check for pipi
if( ! ((pip.size()==1 && pim.size() ==1) || pi0.size()==2)) continue;
// check if histos already made
unsigned int iloc=0; bool found(false);
while(!found&&iloc<_incoming.size()) {
if(_incoming[iloc]==vMeson.pid()&&_outgoing[iloc]==onium[0].pid()) found=true;
else ++iloc;
}
// if histos not made, make them
if(!found) {
MSG_WARNING("MC_Onium_PiPi_Decay" << vMeson.pid() << " " << onium[0].pid() << " "
<< vMeson.mass()-onium[0].mass() << "\n");
continue;
}
// boost to rest frame of the pion pair
FourMomentum q = vMeson.momentum()-onium[0].momentum();
LorentzTransform boost = LorentzTransform::mkFrameTransformFromBeta(q.betaVec());
FourMomentum qp = onium[0].momentum();
FourMomentum ppi= pip.size()==1 ? pip[0].momentum() : pi0[0].momentum();
qp = boost.transform(qp);
ppi = boost.transform(ppi);
double cX=-ppi.p3().unit().dot(qp.p3().unit());
if(pi0.size()==2) {
_mpipi[iloc].second->fill(q.mass());
_hel [iloc].second->fill(abs(cX));
}
else {
_mpipi[iloc].first->fill(q.mass());
_hel [iloc].first->fill(cX);
}
}
}
/// Normalise histograms etc., after the run
void finalize() {
// normalize to unity
for(unsigned int ix=0;ix<_mpipi.size();++ix) {
normalize(_mpipi[ix].first );
normalize(_mpipi[ix].second);
normalize(_hel[ix].first );
normalize(_hel[ix].second);
}
}
//@}
/**
* Incoming onium states
*/
vector<long> _incoming;
/**
* Outgoing onium states
*/
vector<long> _outgoing;
/**
* Histograms for the \f$\pi^+\pi^-\f$ masses
*/
vector<pair<Histo1DPtr,Histo1DPtr> > _mpipi;
/**
* Histmgrams for the helicity angles
*/
vector<pair<Histo1DPtr,Histo1DPtr> > _hel;
};
// The hook for the plugin system
RIVET_DECLARE_PLUGIN(MC_Onium_PiPi_Decay);
}
|