Rivet analyses

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

namespace Rivet {


  /// @brief B -> Xc ell - nu_ell
  class BELLE_2007_I732595 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BELLE_2007_I732595);


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

    /// Book histograms and initialise projections before the run
    void init() {
      // projections
      declare(UnstableParticles(Cuts::abspid == 511 || Cuts::abspid == 521), "UFS");
      // histograms
      for (unsigned int ix = 0; ix < 2; ++ix) {
        book(_p[ix], 1, 1, 1 + 2 * ix);
      }
    }

    void findDecayProducts(const Particle& parent,
                           Particles& em,
                           Particles& ep,
                           Particles& nue,
                           Particles& nueBar,
                           bool& charm) {
      for (const Particle& p : parent.children()) {
        if (PID::isCharmHadron(p.pid())) {
          charm = true;
        }
        else if (p.pid() == PID::EMINUS || p.pid() == PID::MUON) {
          em.push_back(p);
        }
        else if (p.pid() == PID::EPLUS || p.pid() == PID::ANTIMUON) {
          ep.push_back(p);
        }
        else if (p.pid() == PID::NU_E || p.pid() == PID::NU_MU) {
          nue.push_back(p);
        }
        else if (p.pid() == PID::NU_EBAR || p.pid() == PID::NU_MUBAR) {
          nueBar.push_back(p);
        }
        else if (PID::isBottomHadron(p.pid())) {
          findDecayProducts(p, em, ep, nue, nueBar, charm);
        }
        else if (!PID::isHadron(p.pid())) {
          findDecayProducts(p, em, ep, nue, nueBar, charm);
        }
      }
    }

    /// Perform the per-event analysis
    void analyze(const Event& event) {
      if (_edges.empty()) {
        _edges = _p[0]->xEdges();
        for (const string& en : _edges) _eCut.push_back(std::stod(en) * GeV);
      }
      // find and loop over B mesons
      for (const Particle& p : apply<UnstableParticles>(event, "UFS").particles()) {
        if (p.children().empty() || (p.children().size() == 1 && p.children()[1].abspid() == p.abspid()))
          continue;
        // find decay products
        bool charm = false;
        Particles em, ep, nue, nueBar;
        findDecayProducts(p, em, ep, nue, nueBar, charm);
        if (!charm) continue;
        FourMomentum pl, pnu;
        if (em.size() == 1 && nueBar.size() == 1 && em[0].pid() + 1 == -nueBar[0].pid()) {
          pl = em[0].mom();
          pnu = nueBar[0].mom();
        }
        else if (ep.size() == 1 && nue.size() == 1 && nue[0].pid() == -ep[0].pid() + 1) {
          pl = ep[0].mom();
          pnu = nue[0].mom();
        }
        else {
          continue;
        }
        // boost to rest frame
        LorentzTransform boost = LorentzTransform::mkFrameTransformFromBeta(p.mom().betaVec());
        double mX2 = (p.mom() - pl - pnu).mass2();
        pl = boost.transform(pl);
        double Estar = pl.E();
        for (unsigned int ix = 0; ix < 2; ++ix) {
          for (unsigned int ix = 0; ix < _eCut.size(); ++ix) {
            if (Estar > _eCut[ix]) {
              _p[0]->fill(_edges[ix], mX2);
              _p[1]->fill(_edges[ix], sqr(mX2));
            }
          }
        }
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      // compute <(mx2-<mx2>)^2> = <mx4>-<mx2>^2
      BinnedEstimatePtr<string> tmp;
      book(tmp, 1, 1, 2);
      for (unsigned int ix = 0; ix < _p[0]->numBins(); ++ix) {
        const double value = _p[1]->bin(ix + 1).mean(2) - sqr(_p[0]->bin(ix + 1).mean(2));
        const double error = value
            * sqrt(sqr(_p[1]->bin(ix + 1).relStdErr(2)) + 4. * sqr(_p[0]->bin(ix + 1).relStdErr(2)));
        tmp->bin(ix + 1).set(value, error);
      }
    }

    /// @}


    /// @name Histograms
    /// @{
    BinnedProfilePtr<string> _p[2];
    vector<string> _edges;
    vector<double> _eCut;
    /// @}
  };


  RIVET_DECLARE_PLUGIN(BELLE_2007_I732595);

}