Rivet analyses

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

namespace Rivet {


  /// @brief B -> X_s gamma spectrum
  class BELLE_2015_I1330289 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BELLE_2015_I1330289);


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

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

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

      // Book histograms
      book(_h_spectrum, 1, 1, 2);
      book(_nBottom, "TMP/BottomCounter");
    }


    void findDecayProducts(const Particle& mother,
                           unsigned int& nK0,
                           unsigned int& nKp,
                           unsigned int& nKm,
                           FourMomentum& ptot) {
      for (const Particle& p : mother.children()) {
        int id = p.pid();
        if (id == PID::KPLUS) {
          ++nKp;
          ptot += p.momentum();
        }
        else if (id == PID::KMINUS) {
          ++nKm;
          ptot += p.momentum();
        }
        else if (id == PID::K0S) {
          ++nK0;
          ptot += p.momentum();
        }
        else if (id == PID::PI0 || id == PID::PIPLUS || id == PID::PIMINUS) {
          ptot += p.momentum();
        }
        else if (!p.children().empty()) {
          findDecayProducts(p, nK0, nKp, nKm, ptot);
        }
        else
          ptot += p.momentum();
      }
    }


    /// Perform the per-event analysis
    void analyze(const Event& event) {

      // Loop over bottoms
      for (const Particle& bottom : apply<UnstableParticles>(event, "UFS").particles()) {
        if (bottom.pid() != -521 && bottom.pid() != -511) continue;
        FourMomentum pgamma(0., 0., 0., 0.);
        unsigned int ngamma = 0;
        bool fs = true;
        for (const Particle& child : bottom.children()) {
          if (child.pid() == bottom.pid()) {
            fs = false;
            break;
          }
          else if (child.pid() == PID::PHOTON) {
            ngamma += 1;
            pgamma += child.momentum();
          }
        }
        if (!fs) continue;
        _nBottom->fill();
        if (ngamma != 1) continue;
        unsigned int nK0(0), nKp(0), nKm(0);
        FourMomentum p_tot(0, 0, 0, 0);
        findDecayProducts(bottom, nK0, nKp, nKm, p_tot);
        unsigned int nk = nKp - nKm + nK0;
        if (nk % 2 == 1) {
          p_tot -= pgamma;
          _h_spectrum->fill(p_tot.mass() / GeV);
        }
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      scale(_h_spectrum, 1e6 / _nBottom->sumW());
      // multiply by the bin width
      for (size_t ix = 0; ix < _h_spectrum->numBins(); ++ix) {
        _h_spectrum->bin(ix + 1).scaleW(_h_spectrum->bin(ix + 1).xWidth());
      }
    }

    /// @}


    /// @name Histograms
    /// @{
    Histo1DPtr _h_spectrum;
    CounterPtr _nBottom;
    /// @}
  };


  RIVET_DECLARE_PLUGIN(BELLE_2015_I1330289);

}