Rivet analyses

title: BESIII_2019_I1756876

Cross section for $e^+e^-\to D^+D^-\pi^+\pi^-$ for $E_{\text{CMS}}=4.36\to4.60$ GeV

Experiment: BESIII (BEPC)

Inspire ID: 1756876

Status: VALIDATED

Authors: - Peter Richardson

References: - arXiv: 1909.12478

Beams: e- e+

Beam energies: (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)GeV

Run details: - e+e- to hadrons

Cross section for $e^+e^-\to D^+D^-\pi^+\pi^-$ for $E_{\text{CMS}}=4.36\to4.60$ GeV. The cross sections for the subprocesses $e^+e^-\to D_1(2420)^\pm D^\mp$ and $e^+e^-\to \psi(3770) \pi^+\pi^-$ are measured.

Source code:BESIII_2019_I1756876.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/FinalState.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief Cross section for D+D- pi+ pi- (D1 D and psi(3770) pi+pi- subprocesses) class BESIII_2019_I1756876 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2019_I1756876);


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

/// Book histograms and initialise projections before the run
void init() {
  // Initialise and register projections
  declare(FinalState(), "FS");
  declare(UnstableParticles(), "UFS");
  // Book histograms
  book(_nD1D, 1, 1, 1);
  book(_nPsi, 1, 1, 2);
  for (const string& en : _nD1D.binning().edges<0>()) {
    const double eval = stod(en) * MeV;
    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");
  bool matched = false;
  for (const Particle& p1 : ufs.particles(Cuts::abspid == 411)) {
    int sign = p1.pid() / 411;
    map<long, int> nRes = nCount;
    int ncount = ntotal;
    findChildren(p1, nRes, ncount);
    matched = false;
    for (const Particle& p2 : ufs.particles(Cuts::pid == -sign * 411)) {
      map<long, int> nRes2 = nRes;
      int ncount2 = ncount;
      findChildren(p2, 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) break;
    }
    if (matched) break;
  }
  if (!matched) vetoEvent;
  // psi(3770) pi+pi-
  for (const Particle& p1 : ufs.particles(Cuts::abspid == 30443)) {
    if (p1.children().empty()) continue;
    map<long, int> nRes = nCount;
    int ncount = ntotal;
    findChildren(p1, nRes, ncount);
    // psi(3770) pi+pi-
    if (ncount != 2) continue;
    bool matched = true;
    for (const auto& val : nRes) {
      if (abs(val.first) == 211) {
        if (val.second != 1) {
          matched = false;
          break;
        }
      }
      else if (val.second != 0) {
        matched = false;
        break;
      }
    }
    if (matched) {
      _nPsi->fill(_sqs);
      return;
    }
  }
  // D1 D
  for (const Particle& p1 : ufs.particles(Cuts::abspid == 10413)) {
    if (p1.children().empty()) continue;
    int sign = p1.pid() / 10413;
    map<long, int> nRes = nCount;
    int ncount = ntotal;
    findChildren(p1, nRes, ncount);
    matched = false;
    for (const Particle& p2 : ufs.particles(Cuts::pid == -sign * 411)) {
      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) {
      _nD1D->fill(_sqs);
      return;
    }
  }
}

/// Normalise histograms etc., after the run
void finalize() {
  double fact = crossSection() / sumOfWeights() / picobarn;
  scale(_nD1D, fact);
  scale(_nPsi, fact);
}

/// @}

/// @name Histograms
/// @{
BinnedHistoPtr<string> _nD1D, _nPsi;
string _sqs = "";
/// @}

};

RIVET_DECLARE_PLUGIN(BESIII_2019_I1756876);

} ```