Rivet analyses

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

namespace Rivet {


  /// @brief B -> pi, eta and omega decays
  class BABAR_2012_I1125973 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BABAR_2012_I1125973);


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

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

      // Initialise and register projections
      declare(UnstableParticles(Cuts::pid == PID::BPLUS || Cuts::pid == PID::B0), "UFS");

      // histograms
      for (unsigned int ix = 0; ix < 2; ++ix) {
        book(_h_B0_pi[ix], 1, 1, ix + 1);
        book(_h_Bp_pi[ix], 2, 1, ix + 1);
        book(_nB[ix], "TMP/nB_" + toString(ix + 1));
      }
      book(_h_omega, 3, 1, 1);
      book(_h_eta, 4, 1, 1);
    }

    // Calculate the Q2 using mother and daughter charged lepton
    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) {
      // Get B+ Mesons
      for (const Particle& p : apply<UnstableParticles>(event, "UFS").particles()) {
        if (p.pid() == PID::B0) {
          _nB[0]->fill();
          if (isSemileptonicDecay(p, {PID::PIMINUS, PID::POSITRON, PID::NU_E})
              || isSemileptonicDecay(p, {PID::PIMINUS, PID::ANTIMUON, PID::NU_MU})) {
            double Q2 = q2(p, PID::PIMINUS);
            _h_B0_pi[0]->fill(Q2);
            _h_B0_pi[1]->fill(Q2);
          }
        }
        else {
          _nB[1]->fill();
          if (isSemileptonicDecay(p, {PID::PI0, PID::POSITRON, PID::NU_E})
              || isSemileptonicDecay(p, {PID::PI0, PID::ANTIMUON, PID::NU_MU})) {
            double Q2 = q2(p, PID::PI0);
            _h_Bp_pi[0]->fill(Q2);
            _h_Bp_pi[1]->fill(Q2);
          }
          else if (isSemileptonicDecay(p, {PID::OMEGA, PID::POSITRON, PID::NU_E})
                   || isSemileptonicDecay(p, {PID::OMEGA, PID::ANTIMUON, PID::NU_MU})) {
            _h_omega->fill(q2(p, PID::OMEGA));
          }
          else if (isSemileptonicDecay(p, {PID::ETA, PID::POSITRON, PID::NU_E})
                   || isSemileptonicDecay(p, {PID::ETA, PID::ANTIMUON, PID::NU_MU})) {
            _h_eta->fill(q2(p, PID::ETA));
          }
        }
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      // BR in units of 10^{-7}
      for (unsigned int ix = 0; ix < 2; ++ix) {
        scale(_h_B0_pi[ix], 1e7 / *_nB[0]);
        scale(_h_Bp_pi[ix], 1e7 / *_nB[1]);
      }
      scale(_h_omega, 1e7 / *_nB[1]);
      scale(_h_eta, 1e7 / *_nB[1]);
    }

    /// @}


    /// @name Histograms
    /// @{
    CounterPtr _nB[2];
    Histo1DPtr _h_B0_pi[2], _h_Bp_pi[2], _h_omega, _h_eta;
    /// @}
  };


  RIVET_DECLARE_PLUGIN(BABAR_2012_I1125973);

}