Rivet analyses

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

namespace Rivet {


  /// @brief J/psi and psi(2S) in Upsilon(1S) decays
  class BELLE_2016_I1454405 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BELLE_2016_I1454405);


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

    /// Book histograms and initialise projections before the run
    void init() {
      // Initialise and register projections
      declare(UnstableParticles(Cuts::pid == 553), "UFS");
      //histos
      for (unsigned int ix = 0; ix < 2; ++ix)
        for (unsigned int iy = 0; iy < 2; ++iy) book(_h[ix][iy], 1, 1 + ix, 1 + iy);
      book(_nUps, "TMP/nUps");
    }

    /// Recursively walk the decay tree to find decay products of @a p
    void findDecayProducts(Particle mother, Particles& unstable) {
      for (const Particle& p : mother.children()) {
        const int id = abs(p.pid());
        if (id == 443 || id == 100443) {
          unstable.push_back(p);
        }
        if (!p.children().empty()) findDecayProducts(p, unstable);
      }
    }

    /// Perform the per-event analysis
    void analyze(const Event& event) {
      // Find the Upsilons among the unstables
      for (const Particle& ups : apply<UnstableParticles>(event, "UFS").particles()) {
        _nUps->fill();
        // boost to rest frame
        LorentzTransform boost;
        if (ups.p3().mod() > 1 * MeV)
          boost = LorentzTransform::mkFrameTransformFromBeta(ups.momentum().betaVec());
        // find  psi/psi(2S)
        Particles unstable;
        findDecayProducts(ups, unstable);
        // loop over psi/psi(2S)
        for (const Particle& psi : unstable) {
          double Pmax = 0.5 * (sqr(ups.mass()) - sqr(psi.mass())) / ups.mass();
          const FourMomentum p2 = boost.transform(psi.momentum());
          const double xP = p2.p3().mod() / Pmax;
          if (psi.pid() == 443) {
            _h[0][0]->fill(xP);
            _h[1][0]->fill(xP);
          }
          else {
            _h[0][1]->fill(xP);
            _h[1][1]->fill(xP);
          }
        }
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      for (unsigned int ix = 0; ix < 2; ++ix)
        for (unsigned int iy = 0; iy < 2; ++iy) scale(_h[ix][iy], 1e4 / *_nUps);
    }

    /// @}


    /// @name Histograms
    /// @{
    Histo1DPtr _h[2][2];
    CounterPtr _nUps;
    /// @}
  };


  RIVET_DECLARE_PLUGIN(BELLE_2016_I1454405);

}