Rivet analyses

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

namespace Rivet {


  /// @brief Excited Lambda_c spectra
  class ARGUS_1997_I440304 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(ARGUS_1997_I440304);


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

    /// Book histograms and initialise projections before the run
    void init() {
      // projections
      declare(Beam(), "Beams");
      declare(UnstableParticles(), "UFS");
      // book histos
      book(_h_rate1,"TMP/tot_1",refData(1,1,1));
      book(_h_rate2,"TMP/tot_2",refData(1,2,1));
      book(_h_x,2,1,1);
    }


    void findDecayProducts(Particle parent, Particles & Lambda_c, Particles & pions,unsigned int & nstable) {
      for(const Particle & p : parent.children()) {
    if(p.abspid()==4122) {
      Lambda_c.push_back(p);
      ++nstable;
    }
    else if(p.abspid()==PID::PIPLUS) {
      pions.push_back(p);
      ++nstable;
    }
    else if(!p.children().empty())
      findDecayProducts(p,Lambda_c,pions,nstable);
    else
      ++nstable;
      }
    }

    /// Perform the per-event analysis
    void analyze(const Event& event) {
      static const int id2595 = 102142;
      // Get beams and average beam momentum
      const ParticlePair& beams = apply<Beam>(event, "Beams").beams();
      const double Emax = ( beams.first.p3().mod() + beams.second.p3().mod() ) / 2.0;
      const double Pmax = sqrt(sqr(Emax)-sqr(2.595));
      const UnstableParticles& ufs = apply<UnstableParticles>(event, "UFS");
      for (const Particle& p : ufs.particles(Cuts::abspid==id2595)) {
    // spectrum
    double xp = p.momentum().p3().mod()/Pmax;
    _h_x->fill(xp);
    Particles Lambda_c,pions;
    unsigned int nstable(0);
    findDecayProducts(p,Lambda_c,pions,nstable);
    if(nstable==3&&pions.size()==2&&Lambda_c.size()==1) {
      _h_rate1->fill(xp);
      _h_rate2->fill(xp);
    }
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      normalize(_h_x);
      // br for lambda_c mode from pdg 2018
      double br = 0.0623;
      scale(_h_rate1,br*crossSection()/sumOfWeights()/picobarn);
      scale(_h_rate2,br*crossSection()/sumOfWeights()/picobarn);
      Estimate1DPtr tmp;
      book(tmp,1,1,1);
      barchart(_h_rate1,tmp);
      book(tmp,1,2,1);
      barchart(_h_rate2,tmp);
    }

    /// @}


    /// @name Histograms
    /// @{
    Histo1DPtr _h_x,_h_rate1,_h_rate2;
    /// @}


  };


  RIVET_DECLARE_PLUGIN(ARGUS_1997_I440304);

}