Rivet analyses

Cross section for e+e− → 3(π+π−)π0 below 2 GeV by CMD3

Experiment: CMD3 (VEPP-2M)

Inspire ID: 1720610

Status: VALIDATED

Authors: - Peter Richardson

References: - arXiv: 1902.06449

Beams: e+ e-

Beam energies: ANY

Run details: - e+ e- to hadrons

Measurement of the cross section for e+e− → 3(π+π−)π0, and the resonant sub-processes 2(π+π−)ω and 2(π+π−)η, for energies below 2 GeV by the CMD3 experiment

Source code:CMD3_2019_I1720610.cc

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

namespace Rivet {


  /// @brief e+e- -> 3(pi+pi-)pi0
  class CMD3_2019_I1720610 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(CMD3_2019_I1720610);


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

    /// Book histograms and initialise projections before the run
    void init() {

      // Initialise and register projections
      declare(FinalState(), "FS");
      declare(UnstableParticles(Cuts::pid == 221 || Cuts::pid == 223), "UFS");

      // Book histograms
      book(_sigma[0], "TMP/c_all", refData(1, 1, 1));
      book(_sigma[1], "TMP/c_eta", refData(1, 1, 2));
      book(_sigma[2], "TMP/c_omega", refData(1, 1, 3));
    }

    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) {
      // find the final-state particles
      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;
      }
      if (ntotal == 7 && nCount[211] == 3 && nCount[-211] == 3 && nCount[111] == 1) {
        _sigma[0]->fill(sqrtS() / MeV);
      }
      // find omega/phi + eta
      const FinalState& ufs = apply<FinalState>(event, "UFS");
      bool found = false;
      for (const Particle& p : ufs.particles()) {
        if (p.children().empty()) continue;
        map<long, int> nRes = nCount;
        int ncount = ntotal;
        findChildren(p, nRes, ncount);
        // eta/omega 2(pi+pi-)
        if (ncount == 4) {
          bool matched = true;
          for (const auto& val : nRes) {
            if (abs(val.first) == 211) {
              if (val.second != 2) {
                matched = false;
                break;
              }
            }
            else if (val.second != 0) {
              matched = false;
              break;
            }
          }
          if (matched) {
            if (p.pid() == 221) {
              _sigma[1]->fill(sqrtS() / MeV);
            }
            else if (p.pid() == 223) {
              _sigma[2]->fill(sqrtS() / MeV);
            }
            found = true;
            break;
          }
        }
        if (found) break;
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      const double fact = crossSection() / nanobarn / sumOfWeights();
      for (unsigned int ix = 0; ix < 3; ++ix) {
        scale(_sigma[ix], fact);
        Estimate1DPtr tmp;
        book(tmp, 1, 1, 1 + ix);
        barchart(_sigma[ix], tmp);
      }
    }

    /// @}


    /// @name Histograms
    /// @{
    Histo1DPtr _sigma[3];
    /// @}
  };


  RIVET_DECLARE_PLUGIN(CMD3_2019_I1720610);


}