Rivet analyses

title: CMD3_2019_I1720610

Cross section for $e^+e^-\to3(\pi^+\pi^-)\pi^0$ 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 $e^+e^-\to3(\pi^+\pi^-)\pi^0$, and the resonant sub-processes $2(\pi^+\pi^-)\omega$ and $2(\pi^+\pi^-)\eta$, for energies below 2 GeV by the CMD3 experiment

Source code:CMD3_2019_I1720610.cc

```c++ // -- 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);

} ```