Rivet analyses

title: BABAR_2018_I1700745

Cross section for $e^+e^-\to\pi^+\pi^-3\pi^0$ and $\pi^+\pi^-2\pi^0\eta$ between threshold and 4.35 GeV

Experiment: BABAR (PEP-II)

Inspire ID: 1700745

Status: VALIDATED

Authors: - Peter Richardson

References: - arXiv: 1810.11962

Beams: e+ e-

Beam energies: (0.6, 0.6); (0.6, 0.6); (0.6, 0.6); (0.6, 0.6); (0.7, 0.7); (0.7, 0.7); (0.7, 0.7); (0.7, 0.7); (0.8, 0.8); (0.8, 0.8); (0.8, 0.8); (0.8, 0.8); (0.9, 0.9); (0.9, 0.9); (0.9, 0.9); (0.9, 0.9); (1.0, 1.0); (1.0, 1.0); (1.0, 1.0); (1.0, 1.0); (1.1, 1.1); (1.1, 1.1); (1.1, 1.1); (1.1, 1.1); (1.2, 1.2); (1.2, 1.2); (1.2, 1.2); (1.2, 1.2); (1.3, 1.3); (1.3, 1.3); (1.3, 1.3); (1.3, 1.3); (1.4, 1.4); (1.4, 1.4); (1.4, 1.4); (1.4, 1.4); (1.5, 1.5); (1.5, 1.5); (1.5, 1.5); (1.5, 1.5); (1.6, 1.6); (1.6, 1.6); (1.6, 1.6); (1.6, 1.6); (1.7, 1.7); (1.7, 1.7); (1.7, 1.7); (1.7, 1.7); (1.8, 1.8); (1.8, 1.8); (1.8, 1.8); (1.8, 1.8); (1.9, 1.9); (1.9, 1.9); (1.9, 1.9); (1.9, 1.9); (2.0, 2.0); (2.0, 2.0); (2.0, 2.0); (2.0, 2.0); (2.1, 2.1); (2.1, 2.1); (2.1, 2.1); (2.1, 2.1); (2.2, 2.2)GeV

Run details: - e+e- to hadrons

Measurement of the cross section for $e^+e^-\to\pi^+\pi^-3\pi^0$ and $\pi^+\pi^-2\pi^0\eta$ between threshold and 4.35 GeV. The cross sections for the $\pi^+\pi^-\eta$, $\omega\pi^0\pi^0$ and $\omega\pi^0\eta$ resonant contributions are also measured.

Source code:BABAR_2018_I1700745.cc

```c++ // -- C++ --

include "Rivet/Analysis.hh"

include "Rivet/Projections/FinalState.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief e+e- -> pi+pi- and 3pi0 or 2pi0eta class BABAR_2018_I1700745 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BABAR_2018_I1700745);


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

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


  // Initialise and register projections
  declare(FinalState(), "FS");
  declare(UnstableParticles(), "UFS");

  for (size_t ix = 0; ix < 5; ++ix) {
    book(_sigma[ix], 1 + ix, 1, 1);
    for (const string& en : _sigma[0].binning().edges<0>()) {
      const double eval = std::stod(en) * GeV;
      if (isCompatibleWithSqrtS(eval)) {
        _sqs = en;
        break;
      }
    }
  }
  if (_sqs.empty() && isCompatibleWithSqrtS(1.075)) {
    _sqs = "1.075";
  }
  else
    raiseBeamErrorIf(_sqs.empty());
}

void findChildren(const Particle& p, map<long, int>& nRes, int& ncount) const {
  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) {
  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 == 5 && nCount[211] == 1 && nCount[-211] == 1 && nCount[111] == 3) {
    _sigma[0]->fill(_sqs);
  }
  const FinalState& ufs = apply<FinalState>(event, "UFS");
  for (const Particle& p : ufs.particles()) {
    if (p.children().empty()) continue;
    if (p.pid() == 221 || p.pid() == 223) { // find eta/omegas
      map<long, int> nRes = nCount;
      int ncount = ntotal;
      findChildren(p, nRes, ncount);
      if (p.pid() == 221) { // eta
        if (ncount == 2) {  // 2 pi eta
          bool matched = true;
          for (const auto& val : nRes) {
            if (abs(val.first) == 211) {
              if (val.second != 1) {
                matched = false;
                break;
              }
            }
            else if (val.second != 0) {
              matched = false;
              break;
            }
          }
          if (matched) _sigma[1]->fill(_sqs);
        }
        else if (ncount == 4) { // 4 pi eta
          bool matched = true;
          for (const auto& val : nRes) {
            if (abs(val.first) == 211) {
              if (val.second != 1) {
                matched = false;
                break;
              }
            }
            else if (abs(val.first) == 111) {
              if (val.second != 2) {
                matched = false;
                break;
              }
            }
            else if (val.second != 0) {
              matched = false;
              break;
            }
          }
          if (matched) _sigma[3]->fill(_sqs);
        }
        for (const Particle& p2 : ufs.particles()) { // pi0 omega eta
          if (p2.pid() != 223) continue;
          map<long, int> nResB = nRes;
          int ncountB = ncount;
          findChildren(p2, nResB, ncountB);
          if (ncountB != 1) continue;
          bool matched = true;
          for (const auto& val : nResB) {
            if (abs(val.first) == 111) {
              if (val.second != 1) {
                matched = false;
                break;
              }
            }
            else if (val.second != 0) {
              matched = false;
              break;
            }
          }
          if (matched) {
            _sigma[4]->fill(_sqs);
            break;
          }
        }
      }
      else {
        if (ncount != 2) continue;
        bool matched = true;
        for (const auto& val : nRes) {
          if (abs(val.first) == 111) {
            if (val.second != 2) {
              matched = false;
              break;
            }
          }
          else if (val.second != 0) {
            matched = false;
            break;
          }
        }
        if (matched) _sigma[2]->fill(_sqs);
      }
    }
  }
}

/// Normalise histograms etc., after the run
void finalize() {
  scale(_sigma, crossSection() / sumOfWeights() / nanobarn);
}
/// @}


/// @name Histograms
/// @{
BinnedHistoPtr<string> _sigma[5];
string _sqs = "";
/// @}

};

RIVET_DECLARE_PLUGIN(BABAR_2018_I1700745);

} ```