Rivet analyses

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

namespace Rivet {


  /// @brief B -> D semi-leptonic
  class BELLE_2015_I1397632 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BELLE_2015_I1397632);


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

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

      // Initialise and register projections

      declare(UnstableParticles(), "UFS");

      // Book histograms
      book(_h_B_Denu, 1, 1, 1);
      book(_h_B_Dmunu, 1, 1, 2);
      book(_h_B_Deplusnu, 2, 1, 1);
      book(_h_B_Dmuplusnu, 2, 1, 2);
      book(_wB0, "/TMP/wB0");
      book(_wBPlus, "/TMP/wBPlus");
    }

    // 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; });
    }

    // Calculate the recoil w using mother and daugher meson
    double recoilW(const Particle& B, int mesonID) {
      // TODO why does that not work with const?
      Particle D = select(B.children(), Cuts::pid == mesonID)[0];
      FourMomentum q = B.mom() - D.mom();
      return (B.mom() * B.mom() + D.mom() * D.mom() - q * q)
          / (2. * sqrt(B.mom() * B.mom()) * sqrt(D.mom() * D.mom()));
    }


    /// Perform the per-event analysis
    void analyze(const Event& event) {
      // Get B0 Mesons
      for (const Particle& p : apply<UnstableParticles>(event, "UFS").particles(Cuts::pid == PID::B0)) {
        _wB0->fill();
        if (isSemileptonicDecay(p, {PID::DMINUS, PID::POSITRON, PID::NU_E}))
          _h_B_Denu->fill(recoilW(p, PID::DMINUS));
        if (isSemileptonicDecay(p, {PID::DMINUS, PID::ANTIMUON, PID::NU_MU}))
          _h_B_Dmunu->fill(recoilW(p, PID::DMINUS));
      }
      // Get B+ Mesons
      for (const Particle& p : apply<UnstableParticles>(event, "UFS").particles(Cuts::pid == PID::BPLUS)) {
        _wBPlus->fill();
        if (isSemileptonicDecay(p, {PID::D0BAR, PID::POSITRON, PID::NU_E}))
          _h_B_Deplusnu->fill(recoilW(p, PID::D0BAR));
        if (isSemileptonicDecay(p, {PID::D0BAR, PID::ANTIMUON, PID::NU_MU}))
          _h_B_Dmuplusnu->fill(recoilW(p, PID::D0BAR));
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      const double hbar = 6.582119569e-25;
      const double t0 = 1.519e-12, tPlus = 1.638e-12;
      scale(_h_B_Denu, 1e15 * hbar / t0 / *_wB0);
      scale(_h_B_Dmunu, 1e15 * hbar / t0 / *_wB0);
      scale(_h_B_Deplusnu, 1e15 * hbar / tPlus / *_wBPlus);
      scale(_h_B_Dmuplusnu, 1e15 * hbar / tPlus / *_wBPlus);
    }

    /// @}


  private:


    /// @name Histograms
    /// @{
    CounterPtr _wB0, _wBPlus;
    Histo1DPtr _h_B_Denu;
    Histo1DPtr _h_B_Dmunu;
    Histo1DPtr _h_B_Deplusnu;
    Histo1DPtr _h_B_Dmuplusnu;
    /// @}
  };


  RIVET_DECLARE_PLUGIN(BELLE_2015_I1397632);


}