Rivet analyses

// -*- 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);

}