Rivet analyses

title: BES_1999_I505287

Mass and angular distributions for $J/\psi\to\gamma K^{0}\bar{K}^{0}$

Experiment: BES (BEPC)

Inspire ID: 505287

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Lett.B 472 (2000) 200-206

Beams: * *

Beam energies: ANY

Run details: - Any process producing J/psi, originally e+e-

Mass and angular distributions for $J/\psi\to\gamma K^{0}\bar{K}^{0}$. The data were read from the figures in the paper.

Source code:BES_1999_I505287.cc

```c++ // -- C++ --

include "Rivet/Analysis.hh"

include "Rivet/Projections/DecayedParticles.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief J/psi -> K0 Kbar0 class BES_1999_I505287 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BES_1999_I505287);


/// @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::K0S);
  PSI.addStable(PID::PI0);
  PSI.addStable(313);
  PSI.addStable(-313);
  declare(PSI, "PSI");
  // histograms
  book(_h_mass, 1, 1, 1);
  for (unsigned int ix = 0; ix < 2; ++ix) {
    book(_h_angle[ix], 2, 1, 1 + ix);
  }
}


/// Perform the per-event analysis
void analyze(const Event& event) {
  // find the J/psi decays
  DecayedParticles PSI = apply<DecayedParticles>(event, "PSI");
  // loop over particles
  for (unsigned int ix = 0; ix < PSI.decaying().size(); ++ix) {
    if (!PSI.modeMatches(ix, 3, mode)) continue;
    const Particle& Kstar0 = PSI.decayProducts()[0].at(313)[0];
    const Particle& KstarB0 = PSI.decayProducts()[0].at(-313)[0];
    FourMomentum phad = Kstar0.mom() + KstarB0.mom();
    _h_mass->fill(phad.mass());
    Particle Kp;
    if (Kstar0.children()[0].pid() == 321 && Kstar0.children()[1].pid() == -211) {
      Kp = Kstar0.children()[0];
    }
    else if (Kstar0.children()[1].pid() == 321 && Kstar0.children()[0].pid() == -211) {
      Kp = Kstar0.children()[1];
    }
    else {
      continue;
    }
    Particle Km;
    if (KstarB0.children()[0].pid() == -321 && KstarB0.children()[1].pid() == 211) {
      Km = KstarB0.children()[0];
    }
    else if (KstarB0.children()[1].pid() == -321 && KstarB0.children()[0].pid() == 211) {
      Km = KstarB0.children()[1];
    }
    else {
      continue;
    }
    const LorentzTransform boost = LorentzTransform::mkFrameTransformFromBeta(phad.betaVec());
    // K*0 decay
    FourMomentum pKstar0 = boost.transform(Kstar0.mom());
    Vector3 axis1 = pKstar0.p3().unit();
    const LorentzTransform boost1 = LorentzTransform::mkFrameTransformFromBeta(pKstar0.betaVec());
    FourMomentum pKp = boost1.transform(boost.transform(Kp.mom()));
    double cTheta1 = pKp.p3().unit().dot(axis1);
    _h_angle[0]->fill(cTheta1);
    Vector3 trans1 = pKp.p3() - cTheta1 * pKp.p3().mod() * axis1;
    // Kbar*0 decay
    FourMomentum pKstarB0 = boost.transform(KstarB0.mom());
    Vector3 axis2 = pKstar0.p3().unit();
    const LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(pKstarB0.betaVec());
    FourMomentum pKm = boost2.transform(boost.transform(Km.mom()));
    double cTheta2 = pKm.p3().unit().dot(axis2);
    _h_angle[0]->fill(cTheta2);
    Vector3 trans2 = pKm.p3() - cTheta1 * pKm.p3().mod() * axis2;
    double chi = abs(atan2(trans1.cross(trans2).dot(axis1), trans1.dot(trans2))) / M_PI * 180.;
    _h_angle[1]->fill(chi);
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  normalize(_h_mass, 1.0, false);
  normalize(_h_angle, 1.0, false);
}

/// @}


/// @name Histograms
/// @{
Histo1DPtr _h_mass, _h_angle[2];
const map<PdgId, unsigned int> mode = {{313, 1}, {-313, 1}, {22, 1}};
/// @}

};

RIVET_DECLARE_PLUGIN(BES_1999_I505287);

} ```