Rivet analyses

title: BESIII_2022_I2129305

Cross section for $e^+e^-\to \pi^+\pi^- D^+D^-$ between 4.19 and 4.946 GeV

Experiment: BESIII (BEPC)

Inspire ID: 2129305

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - arXiv: 2208.00099

Beams: e+ e-

Beam energies: (2.1, 2.1); (2.1, 2.1); (2.1, 2.1); (2.1, 2.1); (2.1, 2.1); (2.1, 2.1); (2.1, 2.1); (2.1, 2.1); (2.1, 2.1); (2.1, 2.1); (2.1, 2.1); (2.1, 2.1); (2.1, 2.1); (2.2, 2.2); (2.2, 2.2); (2.2, 2.2); (2.2, 2.2); (2.2, 2.2); (2.2, 2.2); (2.2, 2.2); (2.2, 2.2); (2.2, 2.2); (2.2, 2.2); (2.3, 2.3); (2.3, 2.3); (2.3, 2.3); (2.3, 2.3); (2.3, 2.3); (2.3, 2.3); (2.3, 2.3); (2.3, 2.3); (2.4, 2.4); (2.4, 2.4); (2.4, 2.4); (2.4, 2.4); (2.4, 2.4); (2.5, 2.5); (2.5, 2.5); (2.5, 2.5)GeV

Run details: - e+e- to hadrons, KS0 and pi0 should be set stable

Cross section for $e^+e^-\to \pi^+\pi^- D^+D^-$ between 4.19 and 4.946 GeV. The cross section for the $\psi_3(3842)$ resonant contribution is also measured.

Source code:BESIII_2022_I2129305.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/FinalState.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief e+e- > pi+pi- D+ D- class BESIII_2022_I2129305 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2022_I2129305);


/// @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 < 2; ++ix) {
    book(_sigma[ix], ix + 1, 1, 1);
    for (const string& en : _sigma[ix].binning().edges<0>()) {
      const double eval = stod(en) * GeV;
      if (isCompatibleWithSqrtS(eval)) {
        _sqs[ix] = en;
        break;
      }
    }
  }
  raiseBeamErrorIf(_sqs[0].empty() && _sqs[1].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");
  bool matched = false;
  for (const Particle& Dp : ufs.particles(Cuts::pid == PID::DPLUS)) {
    if (Dp.children().empty()) continue;
    map<long, int> nRes = nCount;
    int ncount = ntotal;
    findChildren(Dp, nRes, ncount);
    for (const Particle& Dm : ufs.particles(Cuts::pid == PID::DMINUS)) {
      if (Dm.children().empty()) continue;
      map<long, int> nRes2 = nRes;
      int ncount2 = ncount;
      findChildren(Dm, nRes2, ncount2);
      if (ncount2 != 2) continue;
      matched = true;
      for (const auto& val : nRes2) {
        if (abs(val.first) == 211) {
          if (val.second != 1) {
            matched = false;
            break;
          }
        }
        else if (val.second != 0) {
          matched = false;
          break;
        }
      }
      if (matched) {
        _sigma[0]->fill(_sqs[0]);
        if (!Dm.parents().empty() && !Dp.parents().empty()) {
          // see if D+ from psi3
          Particle parent1 = Dp;
          while (!parent1.parents().empty()) {
            parent1 = parent1.parents()[0];
            if (parent1.pid() == 447) break;
          }
          if (parent1.pid() != 447) break;
          // see if D- from psi3
          Particle parent2 = Dm;
          while (!parent2.parents().empty()) {
            parent2 = parent2.parents()[0];
            if (parent2.pid() == 447) break;
          }
          if (parent2.pid() != 447) break;
          if (fuzzyEquals(parent1.momentum(), parent2.momentum())) {
            _sigma[1]->fill(_sqs[1]);
          }
        }
        break;
      }
    }
    if (matched) break;
  }
}


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

/// @}


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

};

RIVET_DECLARE_PLUGIN(BESIII_2022_I2129305);

} ```