Rivet analyses

title: BESIII_2018_I1633425

Cross-section for $e^+e^-\to\pi^0\pi^0\psi(2S)$ for energies between 4.009 to 4.600 GeV

Experiment: BESIII (BEPC)

Inspire ID: 1633425

Status: VALIDATED

Authors: - Peter Richardson

References: - Phys.Rev. D97 (2018) no.5, 052001

Beams: e+ e-

Beam energies: (2.1, 2.1); (2.1, 2.1); (2.2, 2.2); (2.2, 2.2); (2.3, 2.3)GeV

Run details: - e+ e- to hadrons

Cross section for $e^+e^-\to\pi^+\pi^-h_c$ for energies between 3.89 and 4.6 GeV measured by the BESIII collaboration.

Source code:BESIII_2018_I1633425.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/FinalState.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief Cross-section for e+e- -> pi0pi0psi(2S) for energies between 4.009 to 4.600 GeV class BESIII_2018_I1633425 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2018_I1633425);


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

/// Book histograms and initialise projections before the run
void init() {
  declare(FinalState(), "FS");
  declare(UnstableParticles(), "UFS");
  book(_nPsi2, 1, 1, 1);
  for (const string& en : _nPsi2.binning().edges<0>()) {
    const double eval = stod(en) * GeV;
    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);
  for (const Particle& p : fs.particles()) {
    nCount[p.pid()] += 1;
    ++ntotal;
  }
  const FinalState& ufs = apply<FinalState>(event, "UFS");
  for (const Particle& p : ufs.particles()) {
    if (p.children().empty()) continue;
    // find the psi(2S)
    if (p.pid() == 100443) {
      map<long, int> nRes = nCount;
      int ncount = ntotal;
      findChildren(p, nRes, ncount);
      // omega pi+pi-
      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) {
        _nPsi2->fill(_sqs);
        break;
      }
    }
  }
}

/// Normalise histograms etc., after the run
void finalize() {
  scale(_nPsi2, crossSection() / sumOfWeights() / picobarn);
}
/// @}


/// @name Histograms
/// @{
BinnedHistoPtr<string> _nPsi2;
string _sqs = "";
/// @}

};

RIVET_DECLARE_PLUGIN(BESIII_2018_I1633425);

} ```