Rivet analyses

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

namespace Rivet {


  /// @brief B -> Xs gamma
  class BELLE_2009_I825222 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BELLE_2009_I825222);


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

    /// Book histograms and initialise projections before the run
    void init() {
      // Initialise and register projections
      declare(UnstableParticles(Cuts::abspid == 521 || Cuts::abspid == 511), "UFS");
      // Book histograms
      book(_h_br, 1, 1, 1);
      book(_p_E, 1, 1, 2);
      book(_p_E2, "TMP/E2", refData<YODA::BinnedEstimate<string>>(1, 1, 3));
      book(_nBottom, "TMP/BottomCounter");
    }

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

    /// Perform the per-event analysis
    void analyze(const Event& event) {
      if (_edges.empty()) {
        _edges = _h_br->xEdges();
        for (const string& en : _edges) _eCut.push_back(std::stod(en) * GeV);
      }
      // Loop over bottoms
      for (const Particle& bottom : apply<UnstableParticles>(event, "UFS").particles()) {
        // remove mixing entries etc
        if (bottom.children()[0].abspid() == bottom.abspid()) continue;
        _nBottom->fill();
        FourMomentum pgamma(0., 0., 0., 0.);
        unsigned int ngamma = 0;
        for (const Particle& child : bottom.children()) {
          if (child.pid() == PID::PHOTON) {
            ngamma += 1;
            pgamma += child.momentum();
          }
        }
        if (ngamma != 1) continue;
        unsigned int nK0(0), nKp(0), nKm(0);
        FourMomentum p_tot(0, 0, 0, 0);
        findDecayProducts(bottom, nK0, nKp, nKm);
        unsigned int nk = nKp - nKm + nK0;
        if (nk % 2 == 1) {
          const LorentzTransform boost = LorentzTransform::mkFrameTransformFromBeta(
              bottom.momentum().betaVec());
          double eGamma = boost.transform(pgamma).E();
          for (unsigned int ix = 0; ix < _eCut.size(); ++ix) {
            if (eGamma > _eCut[ix]) {
              _h_br->fill(_edges[ix]);
              _p_E->fill(_edges[ix], eGamma);
              _p_E2->fill(_edges[ix], sqr(eGamma));
            }
          }
        }
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      // 1e4 for br ormalization
      scale(_h_br, 1e4 / _nBottom->sumW());
      // dispersion
      BinnedEstimatePtr<string> dispersion;
      book(dispersion, 1, 1, 3);
      for (auto& b : dispersion->bins()) {
        const auto& bE = _p_E->bin(b.index());
        const auto& bE2 = _p_E2->bin(b.index());
        const double val = bE2.mean(2) - sqr(bE.mean(2));
        const double err = val * sqrt(sqr(bE2.stdErr(2) / bE2.mean(2)) + 4. * sqr(bE.stdErr(2) / bE.mean(2)));
        b.set(val, err);
      }
    }

    /// @}


    /// @name Histograms
    /// @{
    BinnedHistoPtr<string> _h_br;
    BinnedProfilePtr<string> _p_E, _p_E2;
    CounterPtr _nBottom;
    vector<string> _edges;
    vector<double> _eCut;
    /// @}
  };


  RIVET_DECLARE_PLUGIN(BELLE_2009_I825222);

}