Rivet analyses

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

namespace Rivet {


  /// @brief gamma gamma -> eta eta
  class BELLE_2010_I862260 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BELLE_2010_I862260);


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

    /// Book histograms and initialise projections before the run
    void init() {
      // Initialise and register projections
      declare(FinalState(), "FS");
      declare(UnstableParticles(), "UFS");
      // book histos
      if (inRange(sqrtS() / GeV, 1.096, 4.)) {
        book(_sigmaEtaEta[0], "TMP/nEtaPi_1", refData(1, 1, 1));
        if (sqrtS() <= 2.) book(_sigmaEtaEta[1], "TMP/nEtaPi_2", refData(1, 1, 2));
        double sMin = 1.096, sMax = 1.12, step = 0.04;
        unsigned int ihist = 2;
        while (sMin < 3.3) {
          if (inRange(sqrtS() / GeV, sMin, sMax)) {
            break;
          }
          sMin = sMax;
          sMax += step;
          ihist += 1;
          if (fuzzyEquals(2.4, sMin)) step = 0.1;
        }
        if (ihist <= 43) book(_h_cTheta, ihist, 1, 1);
      }
      else {
        throw Error("Invalid CMS energy for BELLE_2010_I862260");
      }
    }

    void findChildren(const Particle& p, map<long, int>& nRes, int& ncount) {
      for (const Particle& child : p.children()) {
        if (child.children().empty()) {
          nRes[child.pid()] -= 1;
          --ncount;
        }
        else {
          findChildren(child, nRes, ncount);
        }
      }
    }

    /// Perform the per-event analysis
    void analyze(const Event& event) {
      const UnstableParticles& ufs = apply<UnstableParticles>(event, "UFS");
      Particles etas = ufs.particles(Cuts::pid == PID::ETA);
      if (etas.size() < 2) vetoEvent;
      const FinalState& fs = apply<FinalState>(event, "FS");
      // find the final-state particles
      map<long, int> nCount;
      int ntotal(0);
      for (const Particle& p : fs.particles()) {
        nCount[p.pid()] += 1;
        ++ntotal;
      }
      for (unsigned int ix = 0; ix < etas.size(); ++ix) {
        if (etas[ix].children().empty()) continue;
        map<long, int> nRes = nCount;
        int ncount = ntotal;
        findChildren(etas[ix], nRes, ncount);
        for (unsigned int iy = ix + 1; iy < etas.size(); ++iy) {
          if (etas[iy].children().empty()) continue;
          map<long, int> nRes2 = nRes;
          int ncount2 = ncount;
          findChildren(etas[iy], nRes2, ncount2);
          if (ncount2 != 0) continue;
          bool matched = true;
          for (const auto& val : nRes2) {
            if (val.second != 0) {
              matched = false;
              break;
            }
          }
          if (matched) {
            double cTheta = abs(etas[iy].momentum().z() / etas[iy].momentum().p3().mod());
            if (cTheta <= 0.9) _sigmaEtaEta[0]->fill(sqrtS());
            if (_sigmaEtaEta[1]) _sigmaEtaEta[1]->fill(sqrtS());
            if (_h_cTheta) _h_cTheta->fill(cTheta);
            break;
          }
        }
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      const double fact = crossSection() / nanobarn / sumOfWeights();
      if (_h_cTheta) scale(_h_cTheta, fact);
      for (unsigned int ix = 0; ix < 2; ++ix) {
        if (!_sigmaEtaEta[ix]) continue;
        scale(_sigmaEtaEta[ix], fact);
        Estimate1DPtr tmp;
        book(tmp, 1, 1, 1 + ix);
        barchart(_sigmaEtaEta[ix], tmp);
      }
    }
    /// @}


    /// @name Histograms
    /// @{
    Histo1DPtr _sigmaEtaEta[2], _h_cTheta;
    /// @}
  };


  RIVET_DECLARE_PLUGIN(BELLE_2010_I862260);

}