Rivet analyses

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

namespace Rivet {


  /// @brief  D -> eta semi-leptonic q^2
  class CLEOC_2011_I875526 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(CLEOC_2011_I875526);


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

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

      // Initialise and register projections
      declare(UnstableParticles(), "UFS");
      // histograms
      book(_h_q2_Dp_eta_A, 1, 1, 1);
      book(_h_q2_Dp_eta_B, 1, 1, 2);
      book(_nDp, "TMP/nDp");
    }

    // Calculate the Q2 using mother and daugher meson
    double q2(const Particle& B, int mesonID) {
      FourMomentum q = B.mom() - select(B.children(), Cuts::pid == mesonID)[0];
      return q * q;
    }

    // Check for explicit decay into pdgids
    bool isSemileptonicDecay(const Particle& mother, vector<int> ids) {
      // Trivial check to ignore any other decays but the one in question modulo photons
      const Particles children = mother.children(Cuts::pid != PID::PHOTON);
      if (children.size() != ids.size()) return false;
      // Check for the explicit decay
      return all(ids, [&](int i) { return count(children, hasPID(i)) == 1; });
    }

    /// Perform the per-event analysis
    void analyze(const Event& event) {
      // Loop over D mesons
      for (const Particle& p : apply<UnstableParticles>(event, "UFS").particles(Cuts::abspid == PID::DPLUS)) {
        _nDp->fill();
        if (isSemileptonicDecay(p, {PID::ETA, PID::POSITRON, PID::NU_E})
            || isSemileptonicDecay(p, {PID::ETA, PID::ELECTRON, PID::NU_EBAR})) {
          double q = q2(p, PID::ETA);
          _h_q2_Dp_eta_A->fill(q);
          _h_q2_Dp_eta_B->fill(q);
        }
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      scale(_h_q2_Dp_eta_A, 1. / *_nDp);
      scale(_h_q2_Dp_eta_B, 1. / *_nDp);
    }

    /// @}


    /// @name Histograms
    /// @{
    Histo1DPtr _h_q2_Dp_eta_A, _h_q2_Dp_eta_B;
    CounterPtr _nD0, _nDp;
    /// @}
  };


  RIVET_DECLARE_PLUGIN(CLEOC_2011_I875526);

}