Rivet analyses

// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/DecayedParticles.hh"
#include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {


  /// @brief J/psi -> K*0 Kbar*0
  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);

}