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Rivet analyses reference
BESIII_2011_I894356
Helicity angle distributions in $\chi_{c1}\to \gamma +(\phi,\rho,\omega)$
Experiment: BESIII (BEPC)
Inspire ID: 894356
Status: VALIDATED NOHEPDATA
Authors:
References:
- Phys.Rev.D 83 (2011) 112005
Beams: * *
Beam energies: ANY
Run details:
- Any process producing chi_c1, originally e+e- -> psi(2S)
Measurement of the helicity angles in the decays $\chi_{c1}\to \gamma +(\phi,\rho,\omega)$. The data were read from the plots in the paper amnd may not be corrected for efficiency/acceptance, however the backgrounds given in the paper have been subtracted.
Source code:
BESIII_2011_I894356.cc
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150 | // -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/UnstableParticles.hh"
namespace Rivet {
/// @brief chi_c1 -> gamma +V
class BESIII_2011_I894356 : public Analysis {
public:
/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2011_I894356);
/// @name Analysis methods
/// @{
/// Book histograms and initialise projections before the run
void init() {
// projections
declare(UnstableParticles(Cuts::pid==20443), "UFS");
// histograms
for(unsigned int ix=0;ix<3;++ix)
book(_h[ix],1,1,1+ix);
}
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) {
for (const Particle& p : apply<UnstableParticles>(event, "UFS").particles()) {
if(p.children().size()!=2) continue;
Particle gamma,meson;
// get the photon and the meson
if(p.children()[0].pid()==PID::PHOTON) {
gamma = p.children()[0];
meson = p.children()[1];
}
else if(p.children()[1].pid()==PID::PHOTON) {
gamma = p.children()[1];
meson = p.children()[0];
}
else
continue;
// check the meson
int imode=-1;
if(meson.pid()==333) imode = 0;
else if(meson.pid()==113) imode = 1;
else if(meson.pid()==223) imode = 2;
else continue;
Particle d1,d2,d3;
if(imode==0) {
if(meson.children().size()!=2) continue;
if(meson.children()[0].pid()==-meson.children()[1].pid() &&
meson.children()[0].abspid()==321) {
d1 = meson.children()[0];
d2 = meson.children()[0];
}
else
continue;
}
else if(imode==1) {
if(meson.children().size()!=2) continue;
if(meson.children()[0].pid()==-meson.children()[1].pid() &&
meson.children()[0].abspid()==211) {
d1 = meson.children()[0];
d2 = meson.children()[0];
}
else
continue;
}
else if(imode==2) {
unsigned int ncount=0;
Particles pip,pim,pi0;
findChildren(meson,pim,pip,pi0,ncount);
if(ncount==3 && pim.size()==1 && pip.size()==1 && pi0.size()==1) {
d1=pip[0];
d2=pim[0];
d3=pi0[0];
}
else continue;
}
if(d1.pid()<0) swap(d1,d2);
// boost in chi_c1 frame
LorentzTransform boost1 = LorentzTransform::mkFrameTransformFromBeta(p.momentum().betaVec());
FourMomentum pMeson = boost1.transform(meson.momentum());
FourMomentum p1=boost1.transform(d1.momentum());
FourMomentum p2=boost1.transform(d2.momentum());
Vector3 axis1 = pMeson.p3().unit();
LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(pMeson.betaVec());
p1=boost2.transform(p1);
p2=boost2.transform(p2);
// axis in meson rest frame
Vector3 axis2;
if(imode<2) {
axis2=p1.p3().unit();
}
else {
FourMomentum p3 = boost1.transform(d3.momentum());
p3 = boost2.transform(p3);
axis2=p1.p3().cross(p2.p3()).unit();
}
_h[imode]->fill(axis1.dot(axis2));
}
}
/// Normalise histograms etc., after the run
void finalize() {
for(unsigned int ix=0;ix<3;++ix)
normalize(_h[ix]);
}
/// @}
/// @name Histograms
/// @{
Histo1DPtr _h[3];
/// @}
};
RIVET_DECLARE_PLUGIN(BESIII_2011_I894356);
}
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