Rivet analyses

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

namespace Rivet {


  /// @brief Upsilon -> Upsilon pi+pi-
  class BELLE_2017_I1610301 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BELLE_2017_I1610301);


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

    /// Book histograms and initialise projections before the run
    void init() {
      // Initialise and register projections
      declare(UnstableParticles(), "UFS");
      for (unsigned int ix = 0; ix < 4; ++ix) {
        book(_h_mpipi[ix], 1, 1, ix + 1);
        book(_h_ctheta[ix], 2, 1, ix + 1);
      }
    }

    void findDecayProducts(const Particle& mother,
                           unsigned int& nstable,
                           Particles& pip,
                           Particles& pim,
                           Particles& pi0,
                           Particles& onium) {
      for (const Particle& p : mother.children()) {
        int id = p.pid();
        if (id == PID::PIMINUS) {
          pim.push_back(p);
          ++nstable;
        }
        else if (id == PID::PIPLUS) {
          pip.push_back(p);
          ++nstable;
        }
        else if (id == PID::PI0) {
          pi0.push_back(p);
          ++nstable;
        }
        else if (abs(id) % 1000 == 443 || abs(id) % 1000 == 553) {
          onium.push_back(p);
          ++nstable;
        }
        else if (!p.children().empty()) {
          findDecayProducts(p, nstable, pip, pim, pi0, onium);
        }
        else
          ++nstable;
      }
    }

    /// Perform the per-event analysis
    void analyze(const Event& event) {
      for (const Particle& ups :
           apply<UnstableParticles>(event, "UFS")
               .particles(Cuts::pid == 100553 or Cuts::pid == 200553 or Cuts::pid == 300553)) {
        unsigned int nstable(0);
        Particles pip, pim, pi0, onium;
        findDecayProducts(ups, nstable, pip, pim, pi0, onium);
        // pions and no of products
        if (pip.size() != 1 || pim.size() != 1 || nstable != 3) continue;
        // check for onium
        if (onium.size() != 1) continue;
        if (!(onium[0].pid() == 553 || (ups.pid() == 300553 && onium[0].pid() == 100553))) continue;
        FourMomentum q = pip[0].momentum() + pim[0].momentum();
        // boost particles to upsilon rest frame
        LorentzTransform boost1 = LorentzTransform::mkFrameTransformFromBeta(ups.momentum().betaVec());
        FourMomentum ppi = boost1.transform(pip[0].momentum());
        FourMomentum pUps = boost1.transform(onium[0].momentum());
        q = boost1.transform(q);
        LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(q.betaVec());
        ppi = boost2.transform(ppi);
        pUps = boost2.transform(pUps);
        double ctheta = ppi.p3().unit().dot(pUps.p3().unit());
        if (ups.pid() == 100553) {
          _h_mpipi[0]->fill(q.mass());
          _h_ctheta[0]->fill(ctheta);
        }
        else if (ups.pid() == 200553) {
          _h_mpipi[1]->fill(q.mass());
          _h_ctheta[1]->fill(ctheta);
        }
        else if (ups.pid() == 300553) {
          if (onium[0].pid() == 553) {
            _h_mpipi[2]->fill(q.mass());
            _h_ctheta[2]->fill(ctheta);
          }
          else {
            _h_mpipi[3]->fill(q.mass());
            _h_ctheta[3]->fill(ctheta);
          }
        }
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      for (unsigned int ix = 0; ix < 4; ++ix) {
        normalize(_h_mpipi[ix]);
        normalize(_h_ctheta[ix]);
      }
    }

    ///@}


    /// @name Histograms
    ///@{
    Histo1DPtr _h_mpipi[4];
    Histo1DPtr _h_ctheta[4];
    ///@}
  };


  RIVET_DECLARE_PLUGIN(BELLE_2017_I1610301);

}