Rivet analyses

title: BESIII_2023_I2661512

Cross section for $e^+e^-\to\Delta^{++}\bar{p}\pi^-+\text{c.c}$ for $\sqrt{s}=2.3094\to2.6464$

Experiment: BESIII (BEPC)

Inspire ID: 2661512

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.D 108 (2023) 7, 072010 - arXiv: 2305.12166

Beams: e+ e-

Beam energies: (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)GeV

Run details: - e+e- to hadrons

Measurement of the cross section for $e^+e^-\to\Delta^{++}\bar{p}\pi^-+\text{c.c}$ for $\sqrt{s}=2.3094\to2.6464$ by the BESIII collaboration.

Source code:BESIII_2023_I2661512.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/FinalState.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief e+e- > Delta++ pbar- pi- class BESIII_2023_I2661512 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2023_I2661512);


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

/// Book histograms and initialise projections before the run
void init() {
  declare(FinalState(), "FS");
  declare(UnstableParticles(Cuts::abspid == 2224), "UFS");
  for (size_t ih = 0; ih < 2; ++ih) {
    book(_sigma[ih], 1 + ih, 1, 1);
    for (const string& en : _sigma[ih].binning().edges<0>()) {
      double eval = stod(en);
      if (isCompatibleWithSqrtS(eval)) _sqs = en;
    }
  }
  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;
  }
  // loop over delta++
  for (const Particle& p : apply<FinalState>(event, "UFS").particles()) {
    int sign = -p.pid() / p.abspid();
    map<long, int> nRes = nCount;
    int ncount = ntotal;
    findChildren(p, nRes, ncount);
    bool matched = true;
    for (const auto& val : nRes) {
      if (val.first == 211 * sign || val.first == 2212 * sign) {
        if (val.second != 1) {
          matched = false;
          break;
        }
      }
      else if (val.second != 0) {
        matched = false;
        break;
      }
    }
    if (matched) {
      size_t ih = _sqs == "2.6454"s;
      _sigma[ih]->fill(_sqs);
      break;
    }
  }
}


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

/// @}


/// @name Histograms
/// @{
BinnedHistoPtr<string> _sigma[2];
string _sqs = "";
/// @}

};

RIVET_DECLARE_PLUGIN(BESIII_2023_I2661512);

} ```