Rivet analyses

title: BESIII_2022_I1900094

Polarization in $D^0\to\omega\phi$

Experiment: BESIII (BEPC)

Inspire ID: 1900094

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.Lett. 128 (2022) 1, 011803

Beams: * *

Beam energies: ANY

Run details: - Any process producing D0 mesons

Measurement of polarization in the decay $D^0\to\omega\phi$ by BESIII. Data read from the plots in the paper.

Source code:BESIII_2022_I1900094.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/FinalState.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief D0 -> omega phi class BESIII_2022_I1900094 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2022_I1900094);


/// @name Analysis methods
/// @{

/// Book histograms and initialise projections before the run
void init() {
  // Initialise and register projections
  declare(UnstableParticles(Cuts::abspid == PID::D0), "UFS");
  for (unsigned int ix = 0; ix < 2; ++ix) book(_h[ix], 1, 1, 1 + ix);
}

void findDecayProducts(const Particle& mother,
                       unsigned int& nstable,
                       Particles& pip,
                       Particles& pim,
                       Particles& pi0) {
  for (const Particle& p : mother.children()) {
    int id = p.pid();
    if (id == PID::KPLUS || id == PID::KMINUS || id == PID::K0S || id == PID::K0L) {
      ++nstable;
    }
    else if (id == PID::PIPLUS) {
      pip.push_back(p);
      ++nstable;
    }
    else if (id == PID::PIMINUS) {
      pim.push_back(p);
      ++nstable;
    }
    else if (id == PID::PI0) {
      pi0.push_back(p);
      ++nstable;
    }
    else if (!p.children().empty()) {
      findDecayProducts(p, nstable, pip, pim, pi0);
    }
    else
      ++nstable;
  }
}

/// Perform the per-event analysis
void analyze(const Event& event) {
  for (const Particle& D0 : apply<UnstableParticles>(event, "UFS").particles()) {
    Particle omega, phi;
    if (D0.children()[0].pid() == PID::OMEGA && D0.children()[1].pid() == PID::PHI) {
      omega = D0.children()[0];
      phi = D0.children()[1];
    }
    else if (D0.children()[1].pid() == PID::OMEGA && D0.children()[0].pid() == PID::PHI) {
      omega = D0.children()[1];
      phi = D0.children()[0];
    }
    else
      continue;
    LorentzTransform boost = LorentzTransform::mkFrameTransformFromBeta(D0.momentum().betaVec());
    // first the phi
    if (phi.children().size() == 2 && phi.children()[0].abspid() == PID::KPLUS
        && phi.children()[1].abspid() == PID::KPLUS) {
      // first boost all relevant momenta to D0 rest frame
      FourMomentum pD0 = boost.transform(D0.momentum());
      FourMomentum pphi = boost.transform(phi.momentum());
      FourMomentum pK = boost.transform(phi.children()[0].momentum());
      LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(pphi.betaVec());
      Vector3 axis1 = boost2.transform(pD0).p3().unit();
      Vector3 axis2 = boost2.transform(pK).p3().unit();
      _h[1]->fill(abs(axis1.dot(axis2)));
    }
    // then the omega
    unsigned int nstable(0);
    Particles pip, pim, pi0;
    findDecayProducts(omega, nstable, pip, pim, pi0);
    if (nstable == 3 && pip.size() == 1 && pip.size() == 1 && pi0.size() == 1) {
      FourMomentum pD0 = boost.transform(D0.momentum());
      FourMomentum pomega = boost.transform(omega.momentum());
      FourMomentum ppip = boost.transform(pip[0].momentum());
      FourMomentum ppim = boost.transform(pim[0].momentum());
      LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(pomega.betaVec());
      Vector3 axis = boost2.transform(pD0).p3().unit();
      Vector3 pp = boost2.transform(ppip).p3();
      Vector3 pm = boost2.transform(ppim).p3();
      Vector3 axis2 = pp.cross(pm).unit();
      _h[0]->fill(abs(axis.dot(axis2)));
    }
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  for (unsigned int ix = 0; ix < 2; ++ix) normalize(_h[ix]);
}

/// @}


/// @name Histograms
/// @{
Histo1DPtr _h[2];
/// @}

};

RIVET_DECLARE_PLUGIN(BESIII_2022_I1900094);

} ```