Rivet analyses

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

namespace Rivet {


  /// @brief J/psi and psi(2S) in Upsilon(1S) decays
  class BELLE_2016_I1454405 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BELLE_2016_I1454405);


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

    /// Book histograms and initialise projections before the run
    void init() {
      // Initialise and register projections
      declare(UnstableParticles(Cuts::pid==553), "UFS");
      //histos
      for(unsigned int ix=0;ix<2;++ix)
    for(unsigned int iy=0;iy<2;++iy)
      book(_h[ix][iy],1,1+ix,1+iy);
      book(_nUps,"TMP/nUps");
    }

   /// Recursively walk the decay tree to find decay products of @a p
    void findDecayProducts(Particle mother, Particles& unstable) {
      for(const Particle & p: mother.children()) {
        const int id = abs(p.pid());
    if(id == 443 || id==100443) {
      unstable.push_back(p);
    }
    if(!p.children().empty())
      findDecayProducts(p, unstable);
      }
    }

    /// Perform the per-event analysis
    void analyze(const Event& event) {
      // Find the Upsilons among the unstables
      for(const Particle & ups : apply<UnstableParticles>(event, "UFS").particles()) {
    _nUps->fill();
    // boost to rest frame
    LorentzTransform boost;
    if (ups.p3().mod() > 1*MeV)
      boost = LorentzTransform::mkFrameTransformFromBeta(ups.momentum().betaVec());
    // find  psi/psi(2S)
    Particles unstable;
    findDecayProducts(ups,unstable);
    // loop over psi/psi(2S)
    for(const Particle& psi : unstable) {
      double Pmax = 0.5*(sqr(ups.mass())-sqr(psi.mass()))/ups.mass();
      const FourMomentum p2 = boost.transform(psi.momentum());
      const double xP = p2.p3().mod()/Pmax;
      if(psi.pid()==443) {
        _h[0][0]->fill(xP);
        _h[1][0]->fill(xP);
      }
      else {
        _h[0][1]->fill(xP);
        _h[1][1]->fill(xP);
      }
    }
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      for(unsigned int ix=0;ix<2;++ix)
    for(unsigned int iy=0;iy<2;++iy)
      scale(_h[ix][iy],1e4/ *_nUps);
    }

    /// @}


    /// @name Histograms
    /// @{
    Histo1DPtr _h[2][2];
    CounterPtr _nUps;
    /// @}


  };


  RIVET_DECLARE_PLUGIN(BELLE_2016_I1454405);

}