Rivet analyses

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

namespace Rivet {


  /// @brief Lambda and Lambda bar dists
  class DELPHI_1993_I360638 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(DELPHI_1993_I360638);


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

    /// Book histograms and initialise projections before the run
    void init() {

      // Initialise and register projections
      const ChargedFinalState cfs;
      declare(cfs, "FS");
      declare(UnstableParticles(), "UFS");
      declare(Sphericity(cfs), "Sphericity");

      // Book histograms
      book(_h_x, 1, 1, 1);
      book(_h_rap, 3, 1, 1);
      book(_h_cos, 4, 1, 1);
      book(_m_single, 2, 1, 1);
      book(_m_like, 5, 1, 1);
      book(_m_opposite, 6, 1, 1);
    }


    /// Perform the per-event analysis
    void analyze(const Event& event) {
      // First, veto on leptonic events by requiring at least 4 charged FS particles
      const FinalState& fs = apply<FinalState>(event, "FS");
      const size_t numParticles = fs.particles().size();
      // Even if we only generate hadronic events, we still need a cut on numCharged >= 2.
      if (numParticles < 2) vetoEvent;
      const UnstableParticles& ufs = apply<UnstableParticles>(event, "UFS");
      // lambda
      Particles lambda = ufs.particles(Cuts::pid == PID::LAMBDA);
      Particles lambdabar = ufs.particles(Cuts::pid == -PID::LAMBDA);
      // multiplicities
      _m_single->fill(Ecm, (lambda.size() + lambdabar.size()));
      if (lambda.empty() && lambdabar.empty()) vetoEvent;
      for (const Particle& p : lambda) {
        double xP = 2. * p.p3().mod() / sqrtS();
        _h_x->fill(xP);
      }
      for (const Particle& p : lambdabar) {
        double xP = 2. * p.p3().mod() / sqrtS();
        _h_x->fill(xP);
      }
      if (lambda.size() >= 2) {
        unsigned int npair = lambda.size() / 2;
        _m_like->fill(Ecm, double(npair));
      }
      if (lambdabar.size() >= 2) {
        unsigned int npair = lambdabar.size() / 2;
        _m_like->fill(Ecm, double(npair));
      }
      if (lambda.size() == 0 || lambdabar.size() == 0) return;
      _m_opposite->fill(Ecm, double(max(lambda.size(), lambdabar.size())));
      const Sphericity& sphericity = apply<Sphericity>(event, "Sphericity");
      for (const Particle& p : lambda) {
        const Vector3 momP = p.p3();
        const double enP = p.E();
        const double modP = dot(sphericity.sphericityAxis(), momP);
        const double rapP = 0.5 * std::log((enP + modP) / (enP - modP));
        for (const Particle& pb : lambdabar) {
          const Vector3 momB = pb.p3();
          const double enB = pb.E();
          const double modB = dot(sphericity.sphericityAxis(), momB);
          const double rapB = 0.5 * std::log((enB + modB) / (enB - modB));
          _h_rap->fill(abs(rapP - rapB));
          _h_cos->fill(momP.unit().dot(momB.unit()));
        }
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      scale(_h_x, 1. / sumOfWeights());
      scale(_h_rap, 1. / sumOfWeights());
      scale(_h_cos, 1. / sumOfWeights());
      scale(_m_single, 1. / sumOfWeights());
      scale(_m_like, 1. / sumOfWeights());
      scale(_m_opposite, 1. / sumOfWeights());
    }

    /// @}


    /// @name Histograms
    /// @{
    Histo1DPtr _h_x, _h_rap, _h_cos;
    BinnedHistoPtr<string> _m_single, _m_like, _m_opposite;
    const string Ecm = "91.2";
    /// @}
  };


  RIVET_DECLARE_PLUGIN(DELPHI_1993_I360638);


}