Rivet analyses

title: BESIII_2017_I1794583

Cross section for $e^+e^-\to D\bar{D}$ near the $\psi(3770)$ resonance

Experiment: BESIII (BEPC)

Inspire ID: 1794583

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.D 109 (2024) 11, 114010 - arXiv: 2404.03896 - URN/HDL:11299/199064

Beams: e+ e-

Beam energies: (1.9, 1.9); (1.9, 1.9); (1.9, 1.9); (1.9, 1.9); (1.9, 1.9); (1.9, 1.9); (1.9, 1.9); (1.9, 1.9); (1.9, 1.9); (1.9, 1.9); (1.9, 1.9); (1.9, 1.9); (1.9, 1.9); (1.9, 1.9); (1.9, 1.9); (1.9, 1.9); (1.9, 1.9); (1.9, 1.9); (1.9, 1.9); (1.9, 1.9); (1.9, 1.9); (1.9, 1.9); (1.9, 1.9); (1.9, 1.9); (1.9, 1.9); (1.9, 1.9); (1.9, 1.9); (1.9, 1.9); (1.9, 1.9); (1.9, 1.9); (1.9, 1.9); (1.9, 1.9); (1.9, 1.9); (1.9, 1.9)GeV

Run details: - e+ e- > hadrons

Measurement of the cross section for $e^+e^-\to D\bar{D}$ near the $\psi(3770)$ resonance. The experimental values are taken from PhD thesis of A. Julin together with the extraction of the Born cross section from Phys.Rev.D 109 (2024) 11, 114010.

Source code:BESIII_2017_I1794583.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief e+e- -> D Dbar class BESIII_2017_I1794583 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2017_I1794583);


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

/// Book histograms and initialise projections before the run
void init() {
  // Initialise and register projections
  declare(FinalState(), "FS");
  declare(UnstableParticles(Cuts::abspid == 411 || Cuts::abspid == 421), "UFS");
  book(_sigma[0], 1, 1, 1);
  book(_sigma[1], 2, 1, 1);

  for (const string& en : _sigma[0].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()] -= 1;
      --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 (size_t ix = 0; ix < ufs.particles().size(); ++ix) {
    const Particle& p1 = ufs.particles()[ix];
    map<long, int> nRes = nCount;
    int ncount = ntotal;
    findChildren(p1, nRes, ncount);
    bool matched = false;
    for (size_t iy = ix + 1; iy < ufs.particles().size(); ++iy) {
      const Particle& p2 = ufs.particles()[iy];
      if (p2.pid() != -p1.pid()) continue;
      if (!p2.parents().empty() && p2.parents()[0].pid() == p1.pid()) continue;
      map<long, int> nRes2 = nRes;
      int ncount2 = ncount;
      findChildren(p2, nRes2, ncount2);
      if (ncount2 != 0) continue;
      matched = true;
      for (const auto& val : nRes2) {
        if (val.second != 0) {
          matched = false;
          break;
        }
      }
      if (matched) break;
    }
    if (matched) {
      _sigma[int(p1.abspid() != 421)]->fill(_sqs);
      break;
    }
  }
}


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

/// @}


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

};

RIVET_DECLARE_PLUGIN(BESIII_2017_I1794583); } ```