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+ rho-
  class BABAR_2008_I789011 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BABAR_2008_I789011);


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

    /// Book histograms and initialise projections before the run
    void init() {
      // Initialise and register projections
      declare(Beam(), "Beams");
      declare(UnstableParticles(Cuts::abspid == 213), "UFS");
      declare(FinalState(), "FS");
      // histos
      for (unsigned int ix = 0; ix < 5; ++ix) book(_h[ix], 1, 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 UnstableParticles& ufs = apply<UnstableParticles>(event, "UFS");
      Particle rhoP, rhoM;
      bool matched(false);
      for (const Particle& p : ufs.particles()) {
        if (p.children().empty()) continue;
        map<long, int> nRes = nCount;
        int ncount = ntotal;
        findChildren(p, nRes, ncount);
        matched = false;
        // check for antiparticle
        for (const Particle& p2 : ufs.particles(Cuts::pid == -p.pid())) {
          if (p2.children().empty()) continue;
          map<long, int> nRes2 = nRes;
          int ncount2 = ncount;
          findChildren(p2, nRes2, ncount2);
          if (ncount2 == 0) {
            matched = true;
            for (const auto& val : nRes2) {
              if (val.second != 0) {
                matched = false;
                break;
              }
            }
            // found rho+/-
            if (matched) {
              if (p.pid() > 0) {
                rhoP = p;
                rhoM = p2;
              }
              else {
                rhoP = p2;
                rhoM = p;
              }
              break;
            }
          }
        }
        if (matched) break;
      }
      if (!matched) vetoEvent;
      Particle piP, piM;
      matched = false;
      if (rhoP.children().size() != 2) vetoEvent;
      if (rhoM.children().size() != 2) vetoEvent;
      if (rhoP.children()[0].pid() == 211 && rhoP.children()[1].pid() == 111)
        piP = rhoP.children()[0];
      else if (rhoP.children()[1].pid() == 211 && rhoP.children()[0].pid() == 111)
        piP = rhoP.children()[1];
      else
        vetoEvent;
      if (rhoM.children()[0].pid() == -211 && rhoM.children()[1].pid() == 111)
        piM = rhoM.children()[0];
      else if (rhoM.children()[1].pid() == -211 && rhoM.children()[0].pid() == 111)
        piM = rhoM.children()[1];
      else
        vetoEvent;
      // boost to the rho+ rest frame
      LorentzTransform boost1 = LorentzTransform::mkFrameTransformFromBeta(rhoP.momentum().betaVec());
      Vector3 e1z = rhoP.momentum().p3().unit();
      Vector3 e1y = e1z.cross(axis).unit();
      Vector3 e1x = e1y.cross(e1z).unit();
      Vector3 axis1 = boost1.transform(piP.momentum()).p3().unit();
      double n1x(e1x.dot(axis1)), n1y(e1y.dot(axis1)), n1z(e1z.dot(axis1));
      _h[0]->fill(n1z);
      _h[2]->fill(atan2(n1y, n1x));
      // boost to the rho- frame
      LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(rhoM.momentum().betaVec());
      Vector3 axis2 = boost2.transform(piM.momentum()).p3().unit();
      double n2x(e1x.dot(axis2)), n2y(e1y.dot(axis2)), n2z(e1z.dot(axis2));
      _h[1]->fill(n2z);
      _h[3]->fill(atan2(n2y, n2x));
      _h[4]->fill(axis.dot(rhoP.momentum().p3().unit()));
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      for (unsigned int ix = 0; ix < 5; ++ix) normalize(_h[ix], 1., false);
    }

    /// @}


    /// @name Histograms
    /// @{
    Histo1DPtr _h[5];
    /// @}
  };


  RIVET_DECLARE_PLUGIN(BABAR_2008_I789011);

}