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Rivet analyses reference
BESIII_2017_I1507887
Analysis of $\psi(2S)\to\gamma\chi_{c(1,2)}$ decays using $\chi_{c(1,2)}\to J/\psi\gamma$
Experiment: BESIII (BEPC)
Inspire ID: 1507887
Status: VALIDATED NOHEPDATA
Authors:
References:
- Phys.Rev.D 95 (2017) 7, 072004
Beams: e- e+
Beam energies: (1.8, 1.8) GeV
Run details:
Analysis of the angular distribution of the photons and leptons produced in $e^+e^-\to \psi(2S) \to \gamma\chi_{c(1,2)}$ followed by $\chi_{c(1,2)}\to\gamma J/\psi$ and $J/\psi\to\ell^+\ell^-$ Gives information about the decay and is useful for testing correlations in charmonium decays. N.B. the data was read from the figures in the paper and is not corrected and should only be used qualatively.
Source code:
BESIII_2017_I1507887.cc
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200 | // -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/Beam.hh"
#include "Rivet/Projections/FinalState.hh"
#include "Rivet/Projections/UnstableParticles.hh"
namespace Rivet {
/// @brief psi(2S) -> gamma chi_c1,2
class BESIII_2017_I1507887 : public Analysis {
public:
/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2017_I1507887);
/// @name Analysis methods
/// @{
/// Book histograms and initialise projections before the run
void init() {
// Initialise and register projections
declare(Beam(), "Beams");
declare(UnstableParticles(Cuts::pid==20443 || Cuts::pid==445), "UFS");
declare(FinalState(), "FS");
for(unsigned int ix=0;ix<10;++ix)
book(_h[ix],1,1,1+ix);
}
void findChildren(const Particle & p,map<long,int> & nRes, int &ncount) {
for( const Particle &child : p.children()) {
if(child.children().empty()) {
nRes[child.pid()]-=1;
--ncount;
}
else
findChildren(child,nRes,ncount);
}
}
// 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) {
// cos of 10 degress for cut
static const double cos10 = 0.984807753012208;
// 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();
// types of final state particles
const FinalState& fs = apply<FinalState>(event, "FS");
map<long,int> nCount;
int ntotal(0);
for (const Particle& p : fs.particles()) {
nCount[p.pid()] += 1;
++ntotal;
}
// loop over chi_c states
Particle chi;
bool matched = false;
const UnstableParticles & ufs = apply<UnstableParticles>(event, "UFS");
for (const Particle& p : ufs.particles()) {
if(p.children().empty()) continue;
map<long,int> nRes=nCount;
int ncount = ntotal;
findChildren(p,nRes,ncount);
if(ncount==1) {
matched = true;
for(auto const & val : nRes) {
if(val.first==PID::PHOTON) {
if(val.second!=1) {
matched = false;
break;
}
}
else if(val.second!=0) {
matched = false;
break;
}
}
if(matched) {
chi=p;
break;
}
}
}
if(!matched) vetoEvent;
// have chi_c find psi2S
if(chi.parents().empty() || chi.children().size()!=2) vetoEvent;
Particle psi2S = chi.parents()[0];
if(psi2S.pid()!=100443 || psi2S.children().size()!=2) vetoEvent;
// then the first photon
Particle gamma1;
if(psi2S.children()[0].pid()==PID::PHOTON)
gamma1 = psi2S.children()[0];
else if(psi2S.children()[1].pid()==PID::PHOTON)
gamma1 = psi2S.children()[1];
else
vetoEvent;
// cuts on the photon
if(vetoPhoton(abs(axis.dot(gamma1.p3().unit())))) vetoEvent;
// then the J/psi and second photon
Particle JPsi,gamma2;
if(chi.children()[0].pid()==PID::PHOTON &&
chi.children()[1].pid()==443) {
gamma2 = chi.children()[0];
JPsi = chi.children()[1];
}
else if(chi.children()[1].pid()==PID::PHOTON &&
chi.children()[0].pid()==443) {
gamma2 = chi.children()[1];
JPsi = chi.children()[0];
}
else
vetoEvent;
// cuts on the photon
if(vetoPhoton(abs(axis.dot(gamma2.p3().unit())))) vetoEvent;
// finally the leptons from J/psi decay
if(JPsi.children().size()!=2) vetoEvent;
if(JPsi.children()[0].pid()!=-JPsi.children()[1].pid()) vetoEvent;
if(JPsi.children()[0].abspid()!=PID::EMINUS &&
JPsi.children()[0].abspid()!=PID::MUON) vetoEvent;
Particle lm = JPsi.children()[0];
Particle lp = JPsi.children()[1];
if(lm.pid()<0) swap(lm,lp);
// cut between photons and charged tracks and on charged tracks
Vector3 dGamma[2] = {gamma1.momentum().p3().unit(),
gamma1.momentum().p3().unit()};
Vector3 dl [2] = {lm.momentum().p3().unit(),
lp.momentum().p3().unit()};
for(unsigned int ix=0;ix<2;++ix) {
// angle cut for charged tracks
if(abs(axis.dot(dl[ix]))>0.93) vetoEvent;
// angle between leptons and photons
for(unsigned int iy=0;iy<2;++iy)
if(abs(dGamma[ix].dot(dl[iy]))>cos10) vetoEvent;
}
// type chi state
unsigned int ichi= chi.pid()==445 ? 5 : 0;
// first angle of gamma1 w.r.t beam
_h[ichi]->fill(axis.dot(gamma1.momentum().p3().unit()));
// axis in the chi frame
LorentzTransform boost1 = LorentzTransform::mkFrameTransformFromBeta(chi.momentum().betaVec());
Vector3 e1z = gamma1.momentum().p3().unit();
Vector3 e1y = e1z.cross(axis).unit();
Vector3 e1x = e1y.cross(e1z).unit();
// cos theta_2 and phi 2 distributions
FourMomentum pGamma2 = boost1.transform(gamma2.momentum());
Vector3 axis1 = pGamma2.p3().unit();
_h[ichi+1]->fill(e1z.dot(axis1));
double phi2 = atan2(e1y.dot(axis1),e1x.dot(axis1));
if(phi2<-3.) phi2+=2.*M_PI;
_h[ichi+3]->fill(phi2);
// cos theta_3 and phi 3 distributions
FourMomentum pJpsi = boost1.transform(JPsi.momentum());
FourMomentum plp = boost1.transform( lp.momentum());
Vector3 axis3 = boost1.transform(gamma1.momentum()).p3().unit();
LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(pJpsi.betaVec());
Vector3 axis2 = boost2.transform(plp).p3().unit();
Vector3 e2z = gamma2.momentum().p3().unit();
Vector3 e2y = e2z.cross(axis3).unit();
Vector3 e2x = e2y.cross(e2z).unit();
_h[ichi+2]->fill(e2z.dot(axis2));
double phi3 = atan2(e2y.dot(axis2),e2x.dot(axis2));
if(phi3<-3.) phi3+=2.*M_PI;
_h[ichi+4]->fill(phi3);
}
/// Normalise histograms etc., after the run
void finalize() {
for(unsigned int ix=0;ix<10;++ix) {
normalize(_h[ix]);
}
}
/// @}
/// @name Histograms
/// @{
Histo1DPtr _h[10];
/// @}
};
RIVET_DECLARE_PLUGIN(BESIII_2017_I1507887);
}
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