Rivet analyses

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

namespace Rivet {


  /// @brief B -> omega pi/K
  class BELLE_2006_I735859 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BELLE_2006_I735859);


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

    /// Book histograms and initialise projections before the run
    void init() {
      // Initialise and register projections
      UnstableParticles ufs = UnstableParticles(Cuts::abspid == 511 || Cuts::abspid == 521);
      declare(ufs, "UFS");
      DecayedParticles BB(ufs);
      BB.addStable(310);
      BB.addStable(223);
      declare(BB, "BB");
      // histos
      for (unsigned int ix = 0; ix < 3; ++ix) {
        book(_h[ix], 1, 1, 1 + ix);
      }
    }

    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) {
      DecayedParticles BB = apply<DecayedParticles>(event, "BB");
      // loop over particles
      for (unsigned int ix = 0; ix < BB.decaying().size(); ++ix) {
        unsigned int imode = 0;
        if (BB.modeMatches(ix, 2, mode1) || BB.modeMatches(ix, 2, mode1CC)) {
          imode = 0;
        }
        else if (BB.modeMatches(ix, 2, mode2) || BB.modeMatches(ix, 2, mode2CC)) {
          imode = 1;
        }
        else if (BB.modeMatches(ix, 2, mode3) || BB.modeMatches(ix, 2, mode3CC)) {
          imode = 2;
        }
        else {
          continue;
        }
        const Particle& omega = BB.decayProducts()[ix].at(223)[0];
        // children of the omega
        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)) continue;
        LorentzTransform boost1 = LorentzTransform::mkFrameTransformFromBeta(
            BB.decaying()[ix].mom().betaVec());
        FourMomentum pomega = boost1.transform(omega.mom());
        FourMomentum pPip = boost1.transform(pip[0].mom());
        FourMomentum pPim = boost1.transform(pim[0].mom());
        // boost to omega frame
        LorentzTransform boost3 = LorentzTransform::mkFrameTransformFromBeta(pomega.betaVec());
        pPip = boost3.transform(pPip);
        pPim = boost3.transform(pPim);
        Vector3 axisOmega = pPip.p3().cross(pPim.p3()).unit();
        // helicity angle
        _h[imode]->fill(abs(pomega.p3().unit().dot(axisOmega)));
      }
    }


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

    /// @}


    /// @name Histograms
    /// @{
    Histo1DPtr _h[3];
    const map<PdgId, unsigned int> mode1 = {{223, 1}, {321, 1}};
    const map<PdgId, unsigned int> mode1CC = {{223, 1}, {-321, 1}};
    const map<PdgId, unsigned int> mode2 = {{223, 1}, {211, 1}};
    const map<PdgId, unsigned int> mode2CC = {{223, 1}, {-211, 1}};
    const map<PdgId, unsigned int> mode3 = {{223, 1}, {130, 1}};
    const map<PdgId, unsigned int> mode3CC = {{223, 1}, {310, 1}};
    /// @}
  };


  RIVET_DECLARE_PLUGIN(BELLE_2006_I735859);

}