Rivet analyses

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

namespace Rivet {


  /// @brief J/psi -> eta', eta, pi0 e+e-
  class BESIII_2014_I1287631 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2014_I1287631);


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

    /// Book histograms and initialise projections before the run
    void init() {
      UnstableParticles ufs = UnstableParticles(Cuts::abspid == PID::JPSI);
      declare(ufs, "UFS");
      DecayedParticles psi(ufs);
      psi.addStable(PID::PI0);
      psi.addStable(PID::ETA);
      psi.addStable(PID::ETAPRIME);
      declare(psi, "PSI");
      for (unsigned int ix = 0; ix < 5; ++ix) book(_h[ix], 1, 1, ix + 1);
      book(_h[5], 2, 1, 1);
      book(_c, "TMP/den");
    }


    /// Perform the per-event analysis
    void analyze(const Event& event) {
      // define the decay mode
      static const map<PdgId, unsigned int>& mode0 = {{PID::ETAPRIME, 1}, {PID::PHOTON, 1}};
      static const map<PdgId, unsigned int>& mode1 = {{PID::ETAPRIME, 1}, {11, 1}, {-11, 1}};
      static const map<PdgId, unsigned int>& mode2 = {{PID::ETA, 1}, {11, 1}, {-11, 1}};
      static const map<PdgId, unsigned int>& mode3 = {{PID::PI0, 1}, {11, 1}, {-11, 1}};
      DecayedParticles psi = apply<DecayedParticles>(event, "PSI");
      // loop over particles
      for (unsigned int ix = 0; ix < psi.decaying().size(); ++ix) {
        unsigned int imode = 0;
        if (psi.modeMatches(ix, 2, mode0)) {
          _c->fill();
          continue;
        }
        else if (psi.modeMatches(ix, 3, mode1)) {
          imode = 1;
        }
        else if (psi.modeMatches(ix, 3, mode2)) {
          imode = 2;
        }
        else if (psi.modeMatches(ix, 3, mode3)) {
          imode = 3;
        }
        else
          continue;
        // e+ e-
        const Particle& em = psi.decayProducts()[ix].at(11)[0];
        const Particle& ep = psi.decayProducts()[ix].at(-11)[0];
        double q = (ep.momentum() + em.momentum()).mass();
        if (imode == 1) {
          _h[0]->fill(q);
          _h[1]->fill(q);
          double me = em.mass();
          double beta = sqrt(1. - 4. * sqr(me / q));
          double mJpsi = psi.decaying()[ix].mass();
          double mEta = psi.decayProducts()[ix].at(331)[0].mass();
          double p = sqrt(sqr(1. + sqr(q) / (sqr(mJpsi) - sqr(mEta)))
                          - 4. * sqr(mJpsi * q / (sqr(mJpsi) - sqr(mEta))));
          double fact = beta * GeV / q * (1. + 2. * sqr(me / q)) * pow(p, 3);
          _h[5]->fill(q, 1. / fact);
        }
        else if (imode == 2) {
          _h[2]->fill(q);
          _h[3]->fill(q);
        }
        else {
          _h[4]->fill(q);
        }
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      for (unsigned int ix = 0; ix < 5; ++ix) normalize(_h[ix], 1., false);
      static double alpha = 7.2973525664e-3;
      scale(_h[5], 1.5 * M_PI / alpha / *_c);
    }

    /// @}


    /// @name Histograms
    /// @{
    Histo1DPtr _h[6];
    CounterPtr _c;
    /// @}
  };


  RIVET_DECLARE_PLUGIN(BESIII_2014_I1287631);

}