Rivet analyses

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

namespace Rivet {


  /// @brief Differential decay rates for $D^+\to \{\bar{K}^0,\pi^0\} e^+\nu_e$ from BES
  class BESIII_2017_I1519425 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2017_I1519425);


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

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

      // Initialise and register projections
      declare(UnstableParticles(), "UFS");

      // Book histograms
      book(_h_q2_K, 1, 1, 1);
      book(_h_q2_pi, 2, 1, 1);
    }

    // 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)) {
        if (isSemileptonicDecay(p, {PID::PI0, PID::POSITRON, PID::NU_E})
            || isSemileptonicDecay(p, {PID::PI0, PID::ELECTRON, PID::NU_EBAR})) {
          _h_q2_pi->fill(q2(p, PID::PI0));
        }
        else if (isSemileptonicDecay(p, {-311, PID::POSITRON, PID::NU_E})) {
          _h_q2_K->fill(q2(p, -311));
        }
        else if (isSemileptonicDecay(p, {311, PID::ELECTRON, PID::NU_EBAR})) {
          _h_q2_K->fill(q2(p, 311));
        }
        else if (isSemileptonicDecay(p, {PID::K0S, PID::POSITRON, PID::NU_E})
                 || isSemileptonicDecay(p, {PID::K0S, PID::ELECTRON, PID::NU_EBAR})) {
          _h_q2_K->fill(q2(p, PID::K0S));
        }
        else if (isSemileptonicDecay(p, {PID::K0L, PID::POSITRON, PID::NU_E})
                 || isSemileptonicDecay(p, {PID::K0L, PID::ELECTRON, PID::NU_EBAR})) {
          _h_q2_K->fill(q2(p, PID::K0L));
        }
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      // normalize to unity
      normalize(_h_q2_K);
      normalize(_h_q2_pi);
    }

    /// @}


    /// @name Histograms
    /// @{
    Histo1DPtr _h_q2_K, _h_q2_pi;
    /// @}
  };


  RIVET_DECLARE_PLUGIN(BESIII_2017_I1519425);


}