Rivet analyses

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


namespace Rivet {


  /// @brief gamma gamma -> Lambda Lmabdabar, Sigma0 Sigmabar0
  class BELLE_2006_I727063 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BELLE_2006_I727063);


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

    /// Book histograms and initialise projections before the run
    void init() {
      // Initialise and register projections
      declare(FinalState(), "FS");
      declare(UnstableParticles(Cuts::abspid == 3122 || Cuts::abspid == 3212), "UFS");
      // histograms
      for (unsigned int ix = 0; ix < 2; ++ix) {
        book(_sigma[ix], "TMP/c_" + toString(ix + 1), refData(1, 1, 1 + ix));
      }
    }

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

    /// Perform the per-event analysis
    void analyze(const Event& event) {
      // check the final state
      const FinalState& fs = apply<FinalState>(event, "FS");
      map<long, int> nCount;
      int ntotal(0);
      for (const Particle& p : fs.particles()) {
        nCount[p.pid()] += 1;
        ++ntotal;
      }
      const FinalState& ufs = apply<FinalState>(event, "UFS");
      Particle Lambda, Lambar;
      // loop over baryon
      bool matched = false;
      for (const Particle& p : ufs.particles()) {
        if (p.children().empty() || p.pid() < 0) continue;
        map<long, int> nRes = nCount;
        int ncount = ntotal;
        findChildren(p, nRes, ncount);
        // and antibaryons
        for (const Particle& p2 : ufs.particles()) {
          if (p2.children().empty() || p2.pid() > 0) continue;
          map<long, int> nRes2 = nRes;
          int ncount2 = ncount;
          findChildren(p2, nRes2, ncount2);
          if (ncount2 != 0) continue;
          matched = 2;
          for (const auto& val : nRes2) {
            if (val.second != 0) {
              matched = false;
              break;
            }
          }
          if (matched) {
            Lambda = p;
            Lambar = p2;
            break;
          }
        }
      }
      if (!matched) vetoEvent;
      if (Lambda.pid() != -Lambar.pid()) vetoEvent;
      double cTheta = abs(Lambda.momentum().z() / Lambda.momentum().p3().mod());
      if (cTheta > 0.6) vetoEvent;
      if (Lambda.pid() == 3122)
        _sigma[1]->fill(sqrtS());
      else
        _sigma[0]->fill(sqrtS());
    }


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

    /// @}


    /// @name Histograms
    /// @{
    Histo1DPtr _sigma[2];
    /// @}
  };


  RIVET_DECLARE_PLUGIN(BELLE_2006_I727063);

}