Rivet analyses

title: BELLE_2008_I754089

Transversality angles for $\eta_c\to f_2f^{(\prime)}_2$

Experiment: BELLE (KEKB)

Inspire ID: 754089

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Eur.Phys.J.C 53 (2008) 1-14

Beams: * *

Beam energies: ANY

Run details: - Any process producing eta_c, originally gamma gamma

Transversality angles for $\eta_c\to f_2f^{(\prime)}_2$. The background subtracted data were read from figure 8 in the paper.

Source code:BELLE_2008_I754089.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/DecayedParticles.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief Transversality angles for $\eta_c\to f_2f^{(\prime)}_2$ class BELLE_2008_I754089 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BELLE_2008_I754089);


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

/// Book histograms and initialise projections before the run
void init() {
  // Initialise and register projections
  UnstableParticles ufs = UnstableParticles(Cuts::abspid == 441);
  declare(ufs, "UFS");
  DecayedParticles ETA(ufs);
  ETA.addStable(225);
  ETA.addStable(335);
  declare(ETA, "ETA");
  // histos
  for (unsigned int ix = 0; ix < 2; ++ix) {
    book(_h[ix], 1, 1, 1 + ix);
  }
}


/// Perform the per-event analysis
void analyze(const Event& event) {
  DecayedParticles ETA = apply<DecayedParticles>(event, "ETA");
  // loop over particles
  for (unsigned int ix = 0; ix < ETA.decaying().size(); ++ix) {
    int imode = -1;
    if (ETA.modeMatches(ix, 2, mode1))
      imode = 0;
    else if (ETA.modeMatches(ix, 2, mode2))
      imode = 1;
    else {
      continue;
    }
    Vector3 trans[2];
    bool found = true;
    LorentzTransform boost1 = LorentzTransform::mkFrameTransformFromBeta(
        ETA.decaying()[ix].mom().betaVec());
    Vector3 axis = boost1.transform(ETA.decaying()[ix].children()[0].mom()).p3().unit();
    for (unsigned int iy = 0; iy < ETA.decaying()[ix].children().size(); ++iy) {
      int iMeson = ETA.decaying()[ix].children()[iy].pid() == 225 ? 211 : 321;
      if (ETA.decaying()[ix].children()[iy].children().size() != 2) found = false;
      if (ETA.decaying()[ix].children()[iy].children()[0].pid()
          != -ETA.decaying()[ix].children()[iy].children()[1].pid())
        found = false;
      if (ETA.decaying()[ix].children()[iy].children()[0].abspid() != iMeson) found = false;
      if (!found) break;
      FourMomentum pF2 = boost1.transform(ETA.decaying()[ix].children()[iy].mom());
      LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(pF2.betaVec());
      FourMomentum pMeson = boost2.transform(
          boost1.transform(ETA.decaying()[ix].children()[iy].children()[0].mom()));
      trans[iy] = pMeson.p3().unit() - pMeson.p3().unit().dot(axis) * axis;
    }
    if (!found) continue;
    const double chi = atan2(trans[0].cross(trans[1]).dot(axis), trans[0].dot(trans[1]));
    _h[imode]->fill(chi);
  }
}


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

/// @}


/// @name Histograms
/// @{
Histo1DPtr _h[2];
const map<PdgId, unsigned int> mode1 = {{225, 2}};
const map<PdgId, unsigned int> mode2 = {{225, 1}, {335, 1}};
/// @}

};

RIVET_DECLARE_PLUGIN(BELLE_2008_I754089);

} ```