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157 | // -*- 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 omega omega
class BESIII_2013_I1203841 : public Analysis {
public:
/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2013_I1203841);
/// @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);
PSI.addStable(PID::OMEGA);
declare(PSI, "PSI");
declare(Beam(), "Beams");
// histograms
for(unsigned int ix=0;ix<9;++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);
}
void findChildren(const Particle & p, Particles & pim, Particles & pip,
Particles & pi0, unsigned int &ncount) {
for( const Particle &child : p.children()) {
if(child.pid()==PID::PIPLUS) {
pip.push_back(child);
ncount+=1;
}
else if(child.pid()==PID::PIMINUS) {
pim.push_back(child);
ncount+=1;
}
else if(child.pid()==PID::PI0) {
pi0.push_back(child);
ncount+=1;
}
else if(child.children().empty()) {
ncount+=1;
}
else
findChildren(child,pim,pip,pi0,ncount);
}
}
/// 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 = { { 223,1}, { 333,1},{ 22,1}};
DecayedParticles PSI = apply<DecayedParticles>(event, "PSI");
if( PSI.decaying().size()!=1) vetoEvent;
if(!PSI.modeMatches(0,3,mode)) vetoEvent;
// particles
const Particle & phi = PSI.decayProducts()[0].at(333)[0];
const Particle & omega = PSI.decayProducts()[0].at(223)[0];
const Particle & gam = PSI.decayProducts()[0].at( 22)[0];
_h[0]->fill((omega.momentum()+phi.momentum()).mass());
_h[1]->fill((omega.momentum()+gam.momentum()).mass());
_h[2]->fill((phi .momentum()+gam.momentum()).mass());
double cTheta = axis.dot(gam.p3().unit());
if(vetoPhoton(abs(cTheta))) vetoEvent;
_h[3]->fill(cTheta);
// remaining angles
LorentzTransform boost1 = LorentzTransform::mkFrameTransformFromBeta(PSI.decaying()[0].momentum().betaVec());
FourMomentum pGamma = boost1.transform(gam.momentum());
FourMomentum pOmegaPhi = boost1.transform(omega.momentum()+phi.momentum());
Vector3 e1z = pGamma.p3().unit();
Vector3 e1y = e1z.cross(axis).unit();
Vector3 e1x = e1y.cross(e1z).unit();
LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(pOmegaPhi.betaVec());
Vector3 axis2 = boost2.transform(boost1.transform(phi.momentum())).p3().unit();
_h[5]->fill(e1z.dot(axis2));
double phiPhi = atan2(axis2.dot(e1y),axis2.dot(e1x));
if(phiPhi<0.) phiPhi+=2.*M_PI;
_h[7]->fill(phiPhi);
// now for the phi decays
if(phi.children().size()!=2|| phi.children()[0].pid()!=-phi.children()[1].pid() ||
phi.children()[0].abspid()!=321) vetoEvent;
Particle Km = phi.children()[0];
Particle Kp = phi.children()[1];
if(Kp.pid()<0) swap(Km,Kp);
FourMomentum pKp = boost2.transform(boost1.transform(Kp.momentum()));
FourMomentum pPhi = boost2.transform(boost1.transform(phi.momentum()));
LorentzTransform boost3 = LorentzTransform::mkFrameTransformFromBeta(pPhi.betaVec());
pKp = boost3.transform(pKp);
double cK = axis2.dot(pKp.p3().unit());
_h[6]->fill(cK);
// omega decay
unsigned int ncount=0;
Particles pip,pim,pi0;
findChildren(omega,pim,pip,pi0,ncount);
if( ncount!=3 || !(pim.size()==1 && pip.size()==1 && pi0.size()==1)) vetoEvent;
// boost to omega/phi frame
FourMomentum ppip = boost2.transform(boost1.transform(pip[0].momentum()));
FourMomentum ppim = boost2.transform(boost1.transform(pim[0].momentum()));
FourMomentum pOmega = boost2.transform(boost1.transform(omega.momentum()));
LorentzTransform boost4 = LorentzTransform::mkFrameTransformFromBeta(pOmega.betaVec());
Vector3 axisZ = pOmega.p3().unit();
ppip = boost4.transform(ppip);
ppim = boost4.transform(ppim);
Vector3 norm = ppip.p3().cross(ppim.p3()).unit();
double cOmega = norm.dot(axisZ);
_h[4]->fill(cOmega);
// angle between planes
Vector3 Trans1 = pKp.p3() - cK*pKp.p3().mod()*axis2;
Vector3 Trans2 = norm - cOmega*axisZ;
double chi = atan(Trans1.cross(Trans2).dot(axis2)/Trans1.dot(Trans2));
_h[8]->fill(abs(chi)/M_PI*180.);
}
/// Normalise histograms etc., after the run
void finalize() {
for(unsigned int ix=0;ix<9;++ix)
normalize(_h[ix],1.,false);
}
/// @}
/// @name Histograms
/// @{
Histo1DPtr _h[9];
/// @}
};
RIVET_DECLARE_PLUGIN(BESIII_2013_I1203841);
}
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