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);

}