Rivet analyses

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

namespace Rivet {


  /// @brief B -> Xc ell - nu_ell
  class BABAR_2009_I827787 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BABAR_2009_I827787);


    /// @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 < 6; ++ix) {
        book(_p_X[ix], 1, 1, 1 + ix);
        if (ix < 3) book(_p_n[ix], 2, 1, 1 + ix);
      }
    }
    void findDecayProducts(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_X[0]->xEdges();
      static const double Lambda = 0.65 * GeV;
      // find and loop over Upslion(4S)
      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].momentum();
          pnu = nueBar[0].momentum();
        }
        else if (ep.size() == 1 && nue.size() == 1 && nue[0].pid() == -ep[0].pid() + 1) {
          pl = ep[0].momentum();
          pnu = nue[0].momentum();
        }
        else
          continue;
        // boost to rest frame
        LorentzTransform boost = LorentzTransform::mkFrameTransformFromBeta(p.momentum().betaVec());
        FourMomentum pX = boost.transform(p.momentum() - pl - pnu);
        pl = boost.transform(pl);
        double modp = pl.p3().mod();
        double mX = pX.mass();
        double nX2 = sqr(mX) - 2. * Lambda * pX.t() + sqr(Lambda);
        double m1 = mX, m2 = nX2;
        for (unsigned int ix = 0; ix < 6; ++ix) {
          double Emin = 0.8;
          for (unsigned int iy = 0; iy < _edges.size(); ++iy) {
            if (modp > Emin) _p_X[ix]->fill(_edges[iy], m1);
            Emin += 0.1;
          }
          m1 *= mX;
          if (ix >= 3) continue;
          Emin = 0.8;
          for (unsigned int iy = 0; iy < _edges.size(); ++iy) {
            if (modp > Emin) _p_n[ix]->fill(_edges[iy], m2);
            Emin += 0.1;
          }
          m2 *= nX2;
        }
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() { }

    /// @}


    /// @name Histograms
    /// @{
    BinnedProfilePtr<string> _p_X[6], _p_n[3];
    vector<string> _edges;
    /// @}
  };


  RIVET_DECLARE_PLUGIN(BABAR_2009_I827787);

}