Rivet analyses

title: BESIII_2013_I1203841

Mass and angular distributions in $J/\psi\to\gamma\omega\phi$ decays

Experiment: BESIII (BEPC)

Inspire ID: 1203841

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.D 87 (2013) 3, 032008

Beams: e- e+

Beam energies: (1.6, 1.6)GeV

Run details: - e+e- > J/psi

Measurement of mass and angular distributions in $J/\psi\to\gamma\omega\phi$ decays.

Source code:BESIII_2013_I1203841.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/Beam.hh"

include "Rivet/Projections/DecayedParticles.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief J/psi -> gamma omega omega class BESIII_2013_I1203841 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2013_I1203841);


/// @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::PHI);
  PSI.addStable(PID::OMEGA);
  declare(PSI, "PSI");
  declare(Beam(), "Beams");
  // histograms
  for (unsigned int ix = 0; ix < 9; ++ix) book(_h[ix], 1, 1, 1 + ix);
}

// angle cuts due regions of BES calorimeter
bool vetoPhoton(const double& cTheta) {
  return cTheta > 0.92 || (cTheta > 0.8 && cTheta < 0.86);
}

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) {
  // 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 = {{223, 1}, {333, 1}, {22, 1}};
  DecayedParticles PSI = apply<DecayedParticles>(event, "PSI");
  if (PSI.decaying().size() != 1) vetoEvent;
  if (!PSI.modeMatches(0, 3, mode)) vetoEvent;
  // particles
  const Particle& phi = PSI.decayProducts()[0].at(333)[0];
  const Particle& omega = PSI.decayProducts()[0].at(223)[0];
  const Particle& gam = PSI.decayProducts()[0].at(22)[0];
  _h[0]->fill((omega.momentum() + phi.momentum()).mass());
  _h[1]->fill((omega.momentum() + gam.momentum()).mass());
  _h[2]->fill((phi.momentum() + gam.momentum()).mass());
  double cTheta = axis.dot(gam.p3().unit());
  if (vetoPhoton(abs(cTheta))) vetoEvent;
  _h[3]->fill(cTheta);
  // remaining angles
  LorentzTransform boost1 = LorentzTransform::mkFrameTransformFromBeta(
      PSI.decaying()[0].momentum().betaVec());
  FourMomentum pGamma = boost1.transform(gam.momentum());
  FourMomentum pOmegaPhi = boost1.transform(omega.momentum() + phi.momentum());
  Vector3 e1z = pGamma.p3().unit();
  Vector3 e1y = e1z.cross(axis).unit();
  Vector3 e1x = e1y.cross(e1z).unit();
  LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(pOmegaPhi.betaVec());
  Vector3 axis2 = boost2.transform(boost1.transform(phi.momentum())).p3().unit();
  _h[5]->fill(e1z.dot(axis2));
  double phiPhi = atan2(axis2.dot(e1y), axis2.dot(e1x));
  if (phiPhi < 0.) phiPhi += 2. * M_PI;
  _h[7]->fill(phiPhi);
  // now for the phi decays
  if (phi.children().size() != 2 || phi.children()[0].pid() != -phi.children()[1].pid()
      || phi.children()[0].abspid() != 321)
    vetoEvent;
  Particle Km = phi.children()[0];
  Particle Kp = phi.children()[1];
  if (Kp.pid() < 0) swap(Km, Kp);
  FourMomentum pKp = boost2.transform(boost1.transform(Kp.momentum()));
  FourMomentum pPhi = boost2.transform(boost1.transform(phi.momentum()));
  LorentzTransform boost3 = LorentzTransform::mkFrameTransformFromBeta(pPhi.betaVec());
  pKp = boost3.transform(pKp);
  double cK = axis2.dot(pKp.p3().unit());
  _h[6]->fill(cK);
  // omega decay
  unsigned int ncount = 0;
  Particles pip, pim, pi0;
  findChildren(omega, pim, pip, pi0, ncount);
  if (ncount != 3 || !(pim.size() == 1 && pip.size() == 1 && pi0.size() == 1)) vetoEvent;
  // boost to omega/phi frame
  FourMomentum ppip = boost2.transform(boost1.transform(pip[0].momentum()));
  FourMomentum ppim = boost2.transform(boost1.transform(pim[0].momentum()));
  FourMomentum pOmega = boost2.transform(boost1.transform(omega.momentum()));
  LorentzTransform boost4 = LorentzTransform::mkFrameTransformFromBeta(pOmega.betaVec());
  Vector3 axisZ = pOmega.p3().unit();
  ppip = boost4.transform(ppip);
  ppim = boost4.transform(ppim);
  Vector3 norm = ppip.p3().cross(ppim.p3()).unit();
  double cOmega = norm.dot(axisZ);
  _h[4]->fill(cOmega);
  // angle between planes
  Vector3 Trans1 = pKp.p3() - cK * pKp.p3().mod() * axis2;
  Vector3 Trans2 = norm - cOmega * axisZ;
  double chi = atan(Trans1.cross(Trans2).dot(axis2) / Trans1.dot(Trans2));
  _h[8]->fill(abs(chi) / M_PI * 180.);
}


/// Normalise histograms etc., after the run
void finalize() {
  for (unsigned int ix = 0; ix < 9; ++ix) normalize(_h[ix], 1., false);
}

/// @}


/// @name Histograms
/// @{
Histo1DPtr _h[9];
/// @}

};

RIVET_DECLARE_PLUGIN(BESIII_2013_I1203841);

} ```