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109 | // -*- 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 p pbar
class BESIII_2012_I1079921 : public Analysis {
public:
/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2012_I1079921);
/// @name Analysis methods
/// @{
/// Book histograms and initialise projections before the run
void init() {
// Initialise and register projections
UnstableParticles ufs = UnstableParticles(Cuts::abspid==443 or
Cuts::abspid==100443);
declare(ufs, "UFS");
DecayedParticles PSI(ufs);
declare(PSI, "PSI");
declare(Beam(), "Beams");
// book histos
if (isCompatibleWithSqrtS(3.1,0.001)) {
for(unsigned int ix=0;ix<4;++ix)
book(_h[ix],1,1,1+ix);
}
else if(isCompatibleWithSqrtS(3.686,0.001)) {
book(_h[0],2,1,1);
}
else {
cerr << "testing problem " << sqrtS() << "\n";
throw Error("Unexpected sqrtS ! Only 3.1 and 3.686 GeV are supported");
}
}
// 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 = { { 2212,1}, { -2212,1},{ 22,1}};
DecayedParticles PSI = apply<DecayedParticles>(event, "PSI");
if( PSI.decaying().size()!=1) vetoEvent;
if(sqrtS()>3.2 && PSI.decaying()[0].pid()==443) vetoEvent;
if(!PSI.modeMatches(0,3,mode)) vetoEvent;
const Particle & pp = PSI.decayProducts()[0].at( 2212)[0];
const Particle & pbar = PSI.decayProducts()[0].at(-2212)[0];
const Particle & gam = PSI.decayProducts()[0].at( 22)[0];
double mass = (pp.momentum()+pbar.momentum()).mass()-pp.mass()-pbar.mass();
_h[0]->fill(mass);
if(!_h[1] || mass>0.05) return;
double cTheta = axis.dot(gam.p3().unit());
// photon angle
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 pppbar = boost1.transform(pp.momentum()+pbar.momentum());
Vector3 e1z = pGamma.p3().unit();
Vector3 e1y = e1z.cross(axis).unit();
Vector3 e1x = e1y.cross(e1z).unit();
LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(pppbar.betaVec());
Vector3 axis2 = boost2.transform(boost1.transform(pp.momentum())).p3().unit();
_h[2]->fill(e1z.dot(axis2));
double phi = atan2(axis2.dot(e1y),axis2.dot(e1x))/M_PI*180.;
_h[3]->fill(phi);
}
/// Normalise histograms etc., after the run
void finalize() {
for(unsigned int ix=0;ix<4;++ix)
if(_h[ix]) normalize(_h[ix],1.,false);
}
/// @}
/// @name Histograms
/// @{
Histo1DPtr _h[4];
/// @}
};
RIVET_DECLARE_PLUGIN(BESIII_2012_I1079921);
}
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