Rivet analyses

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

namespace Rivet {


  /// @brief e+e -> rho 0 rho and rho0 phi
  class BABAR_2006_I719949 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BABAR_2006_I719949);


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

    /// Book histograms and initialise projections before the run
    void init() {
      // Initialise and register projections
      declare(Beam(), "Beams");
      declare(UnstableParticles(Cuts::pid == 113 or Cuts::pid == 333), "UFS");
      declare(FinalState(), "FS");
      // histos
      for (unsigned int ix = 0; ix < 3; ++ix) {
        book(_h_hel[ix], 3, 1, 1 + ix);
        if (ix == 2) continue;
        book(_h_sigma[ix], 1, 1, 1 + ix);
        book(_h_prod[ix], 2, 1, 1 + ix);
      }
    }

    void findChildren(const Particle& p, map<long, int>& nRes, int& ncount) {
      for (const Particle& child : p.children()) {
        if (child.children().empty()) {
          nRes[child.pid()] -= 1;
          --ncount;
        }
        else
          findChildren(child, nRes, ncount);
      }
    }

    /// Perform the per-event analysis
    void analyze(const Event& event) {
      // get the axis, direction of incoming electron
      const ParticlePair& beams = apply<Beam>(event, "Beams").beams();
      Vector3 axis;
      if (beams.first.pid() > 0)
        axis = beams.first.momentum().p3().unit();
      else
        axis = beams.second.momentum().p3().unit();
      // types of final state particles
      const FinalState& fs = apply<FinalState>(event, "FS");
      map<long, int> nCount;
      int ntotal(0);
      for (const Particle& p : fs.particles()) {
        nCount[p.pid()] += 1;
        ++ntotal;
      }
      // loop over rho mesons
      const Particles vMesons = apply<UnstableParticles>(event, "UFS").particles();
      Particle vectors[2];
      bool matched(false);
      for (unsigned int ix = 0; ix < vMesons.size(); ++ix) {
        if (vMesons[ix].children().empty()) continue;
        map<long, int> nRes = nCount;
        int ncount = ntotal;
        findChildren(vMesons[ix], nRes, ncount);
        matched = false;
        for (unsigned int iy = ix + 1; iy < vMesons.size(); ++iy) {
          if (vMesons[iy].children().empty()) continue;
          if (vMesons[ix].pid() == 333 && vMesons[iy].pid() == 333) continue;
          map<long, int> nRes2 = nRes;
          int ncount2 = ncount;
          findChildren(vMesons[iy], nRes2, ncount2);
          if (ncount2 == 0) {
            matched = true;
            for (const auto& val : nRes2) {
              if (val.second != 0) {
                matched = false;
                break;
              }
            }
            if (matched) {
              vectors[0] = vMesons[ix];
              vectors[1] = vMesons[iy];
              break;
            }
          }
        }
        if (matched) break;
      }
      if (!matched) vetoEvent;
      if (vectors[0].pid() == 333) swap(vectors[0], vectors[1]);
      if (vectors[0].children().size() != 2) vetoEvent;
      if (vectors[1].children().size() != 2) vetoEvent;
      double cTheta = abs(axis.dot(vectors[0].momentum().p3().unit()));
      if (cTheta > 0.8) vetoEvent;
      if (vectors[0].pid() == vectors[1].pid()) {
        _h_sigma[0]->fill("10.58"s);
        _h_prod[0]->fill(cTheta);
      }
      else {
        _h_sigma[1]->fill("10.58"s);
        _h_prod[1]->fill(cTheta);
      }
      // helicity angles
      double cHel[2];
      for (unsigned int ix = 0; ix < 2; ++ix) {
        int iMeson = vectors[ix].pid() == 113 ? 211 : 321;
        Particle mP;
        if (vectors[ix].children()[0].pid() == iMeson && vectors[ix].children()[1].pid() == -iMeson)
          mP = vectors[ix].children()[0];
        else if (vectors[ix].children()[1].pid() == iMeson && vectors[ix].children()[0].pid() == -iMeson)
          mP = vectors[ix].children()[1];
        else
          vetoEvent;
        // boost to the rho+ rest frame
        LorentzTransform boost1 = LorentzTransform::mkFrameTransformFromBeta(
            vectors[ix].momentum().betaVec());
        Vector3 e1z = vectors[ix].momentum().p3().unit();
        Vector3 axis1 = boost1.transform(mP.momentum()).p3().unit();
        cHel[ix] = e1z.dot(axis1);
      }
      if (vectors[0].pid() == vectors[1].pid()) {
        _h_hel[0]->fill(cHel[0]);
        _h_hel[0]->fill(cHel[1]);
      }
      else {
        _h_hel[1]->fill(cHel[1]);
        _h_hel[2]->fill(cHel[0]);
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      double fact = crossSection() / sumOfWeights() / femtobarn;
      for (unsigned int ix = 0; ix < 3; ++ix) {
        normalize(_h_hel[ix], 1., false);
        if (ix == 2) continue;
        scale(_h_sigma[ix], fact);
        normalize(_h_prod[ix], 1., false);
      }
    }

    /// @}


    /// @name Histograms
    /// @{
    BinnedHistoPtr<string> _h_sigma[2];
    Histo1DPtr _h_prod[2], _h_hel[3];
    /// @}
  };


  RIVET_DECLARE_PLUGIN(BABAR_2006_I719949);

}