Rivet analyses
Analysis of ψ(2S) → γχc(0, 2) decays using χc(0, 2) → π+π−/K+K−
Experiment: BESIII (BEPC)
Inspire ID: 931195
Status: VALIDATED NOHEPDATA
Authors: - Peter Richardson
References: - Phys.Rev.D 84 (2011) 092006
Beams: e- e+
Beam energies: (1.8, 1.8)GeV
Run details: - e+e- > psi(2S)
Analysis of the angular distribution of the photons and mesons produced in e+e− → ψ(2S) → γχc(0, 2) followed by χc(0, 2) → π+π−/K+K−. Gives information about the decay and is useful for testing correlations in charmonium decays. N.B. the distributions were read from the figures in the paper and are not corrected and should only be used qualatively, however the x and y and multipole results are fully corrected.
Source
code:BESIII_2011_I931195.cc
// -*- 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_c0,2
class BESIII_2011_I931195 : public Analysis {
public:
/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2011_I931195);
/// @name Analysis methods
/// @{
/// Book histograms and initialise projections before the run
void init() {
// Initialise and register projections
declare(Beam(), "Beams");
declare(UnstableParticles(Cuts::pid==10441 || Cuts::pid==445), "UFS");
declare(FinalState(), "FS");
for (unsigned int ichi=0;ichi<2;++ichi) {
for (unsigned int imeson=0;imeson<2;++imeson) {
book(_h_thy[ichi][imeson][0],"TMP/h_"+toString(ichi+1)+"_"+toString(imeson+1)+"_gamma",50,-1.,1.);
book(_h_thy[ichi][imeson][1],"TMP/h_"+toString(ichi+1)+"_"+toString(imeson+1)+"_meson",50,-1.,1.);
book(_h_thy[ichi][imeson][2],"TMP/h_"+toString(ichi+1)+"_"+toString(imeson+1)+"_phi" ,50,0.,2.*M_PI);
for(unsigned int iy=0;iy<3;++iy) {
book(_h_exp[ichi][imeson][iy],5+ichi,1+imeson,1+iy);
}
}
}
for (unsigned int ix=0;ix<3;++ix) {
for (unsigned int iy=0;iy<3;++iy) {
book(_c[ix][iy],"TMP/c_"+toString(ix+1)+"_"+toString(iy+1));
}
}
}
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);
}
}
/// Perform the per-event analysis
void analyze(const Event& event) {
static const double cos20=0.9396926207859084;
// 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 ||
chi.children()[0].pid() != -chi.children()[1].pid()) 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;
// now the decay products of the chi_c
Particle mPlus,mMinus;
bool foundMeson=false;
for (unsigned int ix=0;ix<2;++ix) {
if(chi.children()[ix].pid()==PID::PIPLUS ||
chi.children()[ix].pid()==PID::KPLUS ) {
foundMeson=true;
mPlus=chi.children()[ix];
}
else if(chi.children()[ix].pid()==PID::PIMINUS ||
chi.children()[ix].pid()==PID::KMINUS ) {
mMinus=chi.children()[ix];
}
}
if(!foundMeson) vetoEvent;
// cut on photon angles
Vector3 aGamma = gamma1.p3().unit();
double cGammaCut = abs(axis.dot(aGamma));
// type chi state
unsigned int ichi= chi.pid()==445 ? 0 : 1;
// type of meson
unsigned int imeson = mPlus.pid()==PID::PIPLUS ? 0 : 1;
// first angle of gamma1 w.r.t beam
double cGamma = axis.dot(gamma1.momentum().p3().unit());
_h_thy[ichi][imeson][0]->fill(cGamma);
// 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();
FourMomentum pMeson = boost1.transform(mPlus.momentum());
Vector3 axis1 = pMeson.p3().unit();
double cMeson = e1z.dot(axis1);
_h_thy[ichi][imeson][1]->fill(cMeson);
double phi = atan2(e1y.dot(axis1),e1x.dot(axis1))+M_PI;
_h_thy[ichi][imeson][2]->fill(phi);
// moments to extract multipoles for chi_c2
if(ichi==0) {
double sGamma = sqrt(1.-sqr(cGamma));
double sMeson = sqrt(1.-sqr(cMeson));
double a3 = -3./sqrt(2.)*cos(phi)*sqr(sMeson)*2.*sMeson*cMeson*2.*sGamma*cGamma;
double a4 = sqrt(3.)*(3.*sqr(cMeson)-1.)*cos(phi)*2.*sMeson*cMeson*2.*sGamma*cGamma;
double a5 = sqrt(3./2.)*(3.*sqr(cMeson)-1.)*sqr(sGamma)*sqr(sMeson)*(2.*sqr(cos(phi))-1.);
_c[imeson][0]->fill(a3);
_c[imeson][1]->fill(a4);
_c[imeson][2]->fill(a5);
_c[2][0]->fill(a3);
_c[2][1]->fill(a4);
_c[2][2]->fill(a5);
}
// now fill experimental plots with cuts
if(cGammaCut>0.92 || (cGammaCut>0.8 && cGammaCut<0.86)) vetoEvent;
// cut on charged particles
if(abs(axis.dot(mPlus .p3().unit()))>0.93) vetoEvent;
if(abs(axis.dot(mMinus.p3().unit()))>0.93) vetoEvent;
// cut on angle of photon w.r.t. charged particles
if(abs(aGamma.dot(mPlus .p3().unit()))>cos20) vetoEvent;
if(abs(aGamma.dot(mMinus.p3().unit()))>cos20) vetoEvent;
// fill histos
_h_exp[ichi][imeson][0]->fill(cGamma);
_h_exp[ichi][imeson][1]->fill(cMeson);
_h_exp[ichi][imeson][2]->fill(phi);
}
/// Normalise histograms etc., after the run
void finalize() {
// first normalize the histograms
for (unsigned int ichi=0; ichi<2; ++ichi) {
for (unsigned int imeson=0; imeson<2; ++imeson) {
for (unsigned int iy=0; iy<3; ++iy) {
normalize(_h_thy[ichi][imeson][iy]);
normalize(_h_exp[ichi][imeson][iy]);
}
}
}
// extract the x and y values
double x, y, dx, dy;
for (unsigned int ix=0; ix<3; ++ix) {
Estimate0DPtr multX, multY;
book(multX, 1+ix, 1, 1);
book(multY, 1+ix, 1, 2);
divide(_c[ix][0], _c[ix][2], multX);
divide(_c[ix][0], _c[ix][1], multY);
x = multX->val();
dx = multX->totalErrAvg();
y = multY->val();
dy = multY->totalErrAvg();
}
// convert x and y to M1 and E2
double M1 = (3*sqrt(10) + sqrt(30)*x - 2*sqrt(15)*y)/(3.*(sqrt(2) + sqrt(6)*x + 2*sqrt(3)*y));
double E2 = (2*(2*sqrt(3) - 5*sqrt(2)*y - 2*sqrt(3)*sqr(y) + 4*x*(-1 + sqrt(6)*y)))/
((sqrt(6) - 6*y)*(sqrt(2) + sqrt(6)*x + 2*sqrt(3)*y));
double e1 = (-4*sqrt(1.6666666666666667) + 4*sqrt(10)*y)/sqr(sqrt(2) + sqrt(6)*x + 2*sqrt(3)*y);
double e2 = (-4*sqrt(3.3333333333333335)*(2 + sqrt(3)*x))/sqr(sqrt(2) + sqrt(6)*x + 2*sqrt(3)*y);
double e3 = (20*(-sqrt(2) + y*(sqrt(3) + 3*sqrt(2)*y)))/((sqrt(6) - 6*y)*sqr(sqrt(2) + sqrt(6)*x + 2*sqrt(3)*y));
double e4 = (-10*(sqrt(6) - 3*sqrt(2)*x))/(3.*sqr(sqrt(2) + sqrt(6)*x + 2*sqrt(3)*y));
pair<double,double> dM1 = make_pair(sqrt(sqr(e1*dx)+sqr(e2*dy)),sqrt(sqr(e1*dx)+sqr(e2*dy)));
pair<double,double> dE2 = make_pair(sqrt(sqr(e3*dx)+sqr(e4*dy)),sqrt(sqr(e3*dx)+sqr(e4*dy)));
Estimate0DPtr multM1, multM2;
book(multM1, 4, 1, 1);
multM1->set(M1, dM1);
book(multM2, 4, 1, 2);
multM2->set(E2, dE2);
}
/// @}
/// @name Histograms
/// @{
Histo1DPtr _h_exp[2][2][3], _h_thy[2][2][3];
CounterPtr _c[3][3];
/// @}
};
RIVET_DECLARE_PLUGIN(BESIII_2011_I931195);
}