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114 | // -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/Beam.hh"
#include "Rivet/Projections/UnstableParticles.hh"
#include "Rivet/Projections/DecayedParticles.hh"
namespace Rivet {
/// @brief J/psi -> gamma phi phi
class BESIII_2016_I1419650 : public Analysis {
public:
/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2016_I1419650);
/// @name Analysis methods
/// @{
/// Book histograms and initialise projections before the run
void init() {
// Initialise and register projections
UnstableParticles ufs = UnstableParticles(Cuts::abspid==443);
declare(ufs, "UFS");
DecayedParticles PSI(ufs);
PSI.addStable(PID::PHI);
declare(PSI, "PSI");
declare(Beam(), "Beams");
// book histograms
for(unsigned int ix=0;ix<5;++ix)
book(_h[ix],1,1,1+ix);
}
// angle cuts due regions of BES calorimeter
bool vetoPhoton(const double & cTheta) {
return cTheta>0.92 || (cTheta>0.8 && cTheta<0.86);
}
/// Perform the per-event analysis
void analyze(const Event& event) {
// get the axis, direction of incoming electron
const ParticlePair& beams = apply<Beam>(event, "Beams").beams();
Vector3 axis;
if(beams.first.pid()>0)
axis = beams.first .momentum().p3().unit();
else
axis = beams.second.momentum().p3().unit();
// find the J/psi decays
static const map<PdgId,unsigned int> & mode = { { 333,2},{ 22,1}};
DecayedParticles PSI = apply<DecayedParticles>(event, "PSI");
if( PSI.decaying().size()!=1) vetoEvent;
if(!PSI.modeMatches(0,3,mode)) vetoEvent;
// particles
const Particles & phi = PSI.decayProducts()[0].at(333);
const Particle & gam = PSI.decayProducts()[0].at( 22)[0];
_h[0]->fill((phi[0].momentum()+phi[1].momentum()).mass());
double cTheta = axis.dot(gam.p3().unit());
if(vetoPhoton(abs(cTheta))) vetoEvent;
_h[1]->fill(cTheta);
// remaining angles
LorentzTransform boost1 = LorentzTransform::mkFrameTransformFromBeta(PSI.decaying()[0].momentum().betaVec());
FourMomentum pGamma = boost1.transform(gam.momentum());
FourMomentum pPhiPhi= boost1.transform(phi[0].momentum()+phi[1].momentum());
Vector3 e1z = pGamma.p3().unit();
Vector3 e1y = e1z.cross(axis).unit();
Vector3 e1x = e1y.cross(e1z).unit();
LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(pPhiPhi.betaVec());
Vector3 axis2 = boost2.transform(boost1.transform(phi[0].momentum())).p3().unit();
_h[2]->fill(e1z.dot(axis2));
// now for the phi decays
Particle Km[2],Kp[2];
FourMomentum pKp[2],pPhi[2];
for(unsigned int ix=0;ix<2;++ix) {
if(phi[ix].children().size()!=2|| phi[ix].children()[0].pid()!=-phi[ix].children()[1].pid() ||
phi[ix].children()[0].abspid()!=321) vetoEvent;
Km[ix] = phi[ix].children()[0];
Kp[ix] = phi[ix].children()[1];
if(Kp[ix].pid()<0) swap(Km[ix],Kp[ix]);
pKp[ix] = boost2.transform(boost1.transform(Kp[ix].momentum()));
pPhi[ix] = boost2.transform(boost1.transform(phi[ix].momentum()));
LorentzTransform boost3 = LorentzTransform::mkFrameTransformFromBeta(pPhi[ix].betaVec());
pKp[ix] = boost3.transform(pKp[ix]);
}
double cK = axis2.dot(pKp[0].p3().unit());
_h[3]->fill(cK);
Vector3 Trans1 = pKp[0].p3() - cK*pKp[0].p3().mod()*axis2;
Vector3 Trans2 = pKp[1].p3() - axis2.dot(pKp[1].p3())*axis2;
double chi = atan(Trans1.cross(Trans2).dot(axis2)/Trans1.dot(Trans2));
_h[4]->fill(abs(chi)/M_PI*180.);
}
/// Normalise histograms etc., after the run
void finalize() {
for(unsigned int ix=0;ix<5;++ix)
normalize(_h[ix],1.,false);
}
/// @}
/// @name Histograms
/// @{
Histo1DPtr _h[5];
/// @}
};
RIVET_DECLARE_PLUGIN(BESIII_2016_I1419650);
}
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