// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/UnstableParticles.hh"
#include "Rivet/Projections/DecayedParticles.hh"
namespace Rivet {
/// @brief eta -> pi+pi-pi0 and eta' -> pi0pi0pi0$
class BESIII_2015_I1376484 : public Analysis {
public:
/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2015_I1376484);
/// @name Analysis methods
/// @{
/// Book histograms and initialise projections before the run
void init() {
// Initialise and register projections
UnstableParticles ufs = UnstableParticles(Cuts::pid==PID::ETA or
Cuts::pid==PID::ETAPRIME);
declare(ufs, "UFS");
DecayedParticles ETA(ufs);
ETA.addStable(PID::PI0);
ETA.addStable(PID::K0S);
ETA.addStable(PID::ETA);
declare(ETA, "ETA");
for(unsigned int ix=0;ix<2;++ix) {
book(_h[ix ],1,1,1+ix);
book(_h[ix+2],2+ix,1,1);
}
}
/// Perform the per-event analysis
void analyze(const Event& event) {
static const map<PdgId,unsigned int> & mode1 = { {211,1}, {-211,1}, {111,1} };
static const map<PdgId,unsigned int> & mode2 = { {111,3} };
DecayedParticles ETA = apply<DecayedParticles>(event, "ETA");
// loop over particles
for(unsigned int ix=0;ix<ETA.decaying().size();++ix) {
// select right decay mode
if ( ETA.decaying()[ix].pid()==PID::ETA && ETA.modeMatches(ix,3,mode1)) {
const Particle & pi0 = ETA.decayProducts()[ix].at( 111)[0];
const Particle & pip = ETA.decayProducts()[ix].at( 211)[0];
const Particle & pim = ETA.decayProducts()[ix].at(-211)[0];
double s1 = (pi0.momentum()+pim.momentum()).mass2();
double s2 = (pi0.momentum()+pip.momentum()).mass2();
double s3 = (pip.momentum()+pim.momentum()).mass2();
double mOut = pi0.mass()+pip.mass()+pim.mass();
double Q = ETA.decaying()[ix].mass()-mOut;
double X = sqrt(3.)/2./ETA.decaying()[ix].mass()/Q*(s1-s2);
double Y = 3.*(sqr(ETA.decaying()[ix].mass()-pi0.mass())-s3)/2./ETA.decaying()[ix].mass()/Q-1.;
_h[0]->fill(X);
_h[1]->fill(Y);
}
else if ( ETA.modeMatches(ix,3,mode2)) {
const Particles & pi0 = ETA.decayProducts()[ix].at(111);
double s1 = (pi0[2].momentum()+pi0[1].momentum()).mass2();
double s2 = (pi0[2].momentum()+pi0[0].momentum()).mass2();
double s3 = (pi0[0].momentum()+pi0[1].momentum()).mass2();
double mOut = pi0[2].mass()+pi0[0].mass()+pi0[1].mass();
double Q = ETA.decaying()[ix].mass()-mOut;
double X = sqrt(3.)/2./ETA.decaying()[ix].mass()/Q*(s1-s2);
double Y = 3.*(sqr(ETA.decaying()[ix].mass()-pi0[2].mass())-s3)/2./ETA.decaying()[ix].mass()/Q-1.;
double Z = sqr(X)+sqr(Y);
if(ETA.decaying()[ix].pid()==PID::ETA) _h[2]->fill(Z);
else _h[3]->fill(Z);
}
}
}
/// Normalise histograms etc., after the run
void finalize() {
for(unsigned int ix=0;ix<4;++ix)
normalize(_h[ix]);
}
/// @}
/// @name Histograms
/// @{
Histo1DPtr _h[4];
/// @}
};
RIVET_DECLARE_PLUGIN(BESIII_2015_I1376484);
}