Rivet analyses

title: BESIII_2024_I2751832

Cross section for $e^+e^-\to\pi^+\pi^-\pi^0$ between 2.00 and 3.08 GeV

Experiment: BESIII (BEPC)

Inspire ID: 2751832

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - arXiv: 2401.14711

Beams: e+ e-

Beam energies: (1.0, 1.0); (1.0, 1.0); (1.1, 1.1); (1.1, 1.1); (1.1, 1.1); (1.1, 1.1); (1.1, 1.1); (1.1, 1.1); (1.2, 1.2); (1.2, 1.2); (1.2, 1.2); (1.3, 1.3); (1.3, 1.3); (1.4, 1.4); (1.5, 1.5); (1.5, 1.5); (1.5, 1.5); (1.5, 1.5); (1.5, 1.5)GeV

Run details: - e+ e- to hadrons, pi0 set stable

Cross section for $e^+e^-\to\pi^+\pi^-\pi^0$ between 2.00 and 3.08 GeV measured by BESII. The $\rho\pi$ and $\rho(1450)\pi$ subprocesses are also extracted.

Source code:BESIII_2024_I2751832.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/FinalState.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief e+ e- -> pi+ pi- pi0 class BESIII_2024_I2751832 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2024_I2751832);


/// @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 < 3; ++ix) book(_sigma[ix], 1, 1, 1 + ix);

  for (const string& en : _sigma[0].binning().edges<0>()) {
    double eval = stod(en);
    if (isCompatibleWithSqrtS(eval)) {
      _sqs = en;
      break;
    }
  }
  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);
  Particle pip, pim;
  for (const Particle& p : fs.particles()) {
    nCount[p.pid()] += 1;
    ++ntotal;
    if (p.pid() == 211)
      pip = p;
    else if (p.pid() == -211)
      pim = p;
  }
  if (ntotal != 3) vetoEvent;
  if (nCount[-211] == 1 && nCount[211] == 1 && nCount[111] == 1) {
    _sigma[0]->fill(_sqs);
  }
  else {
    vetoEvent;
  }
  const FinalState& ufs = apply<FinalState>(event, "UFS");
  for (const Particle& p : ufs.particles(Cuts::abspid == 113 || Cuts::abspid == 213
                                         || Cuts::abspid == 100113 || Cuts::abspid == 100213)) {
    if (p.children().empty()) continue;
    map<long, int> nRes = nCount;
    int ncount = ntotal;
    findChildren(p, nRes, ncount);
    if (ncount != 1) continue;
    int idOther = 211;
    if (p.pid() == 113 || p.pid() == 100113) {
      idOther = 111;
    }
    else if (p.pid() == 213 || p.pid() == 100213) {
      idOther = -211;
    }
    bool matched = true;
    for (const auto& val : nRes) {
      if (val.first == idOther) {
        if (val.second != 1) {
          matched = false;
          break;
        }
      }
      else if (val.second != 0) {
        matched = false;
        break;
      }
    }
    if (matched) {
      if (p.pid() == 213 || p.pid() == 113)
        _sigma[1]->fill(_sqs);
      else
        _sigma[2]->fill(_sqs);
      break;
    }
    else
      continue;
  }
}


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

/// @}


/// @name Histograms
/// @{
BinnedHistoPtr<string> _sigma[3];
string _sqs = "";
/// @}

};

RIVET_DECLARE_PLUGIN(BESIII_2024_I2751832);

} ```