Rivet analyses

title: BESIII_2024_I2779452

Cross section for $e^+e^-\to\omega \chi_{c(1,2)}$ and $X(3872)$ for $\sqrt{s}=4.66$ to 4.95 GeV

Experiment: BESIII (BEPC)

Inspire ID: 2779452

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.D 110 (2024) 1, 012006 - arXiv: 2404.13840

Beams: e+ e-

Beam energies: (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)GeV

Run details: - e+ e- -> hadrons

Measurement of the cross section for $e^+e^-\to\omega\chi_{c(1,2)}$ and $e^+e^-\to\omega X(3872)$ for $\sqrt{s}=4.66$ to 4.95 GeV. There is no consensus as to the nature of the $X(3872)$ $c\bar{c}$ state and therefore we taken its PDG code to be 9030443, i.e. the first unused code for an undetermined spin one $c\bar{c}$ state. This can be changed using the PID option if a different code is used by the event generator performing the simulation.

Source code:BESIII_2024_I2779452.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/FinalState.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief Cross section for $e^+e^-\to\omega \chi_{c(1,2)}$ and $X(3872)$ for $\sqrt{s}=4.66$ to 4.95 GeV class BESIII_2024_I2779452 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2024_I2779452);


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

/// Book histograms and initialise projections before the run
void init() {
  // set the PDG code
  _pid = getOption<double>("PID", 9030443);
  // projections
  declare(FinalState(), "FS");
  declare(UnstableParticles(), "UFS");
  // histos
  for (size_t ix = 0; ix < 3; ++ix) {
    book(_h[ix], 1 + ix, 1, 1);
  }
  for (const string& en : _h[0].binning().edges<0>()) {
    const double eval = stod(en);
    if (isCompatibleWithSqrtS(eval)) {
      _sqs = en;
      break;
    }
  }
  raiseBeamErrorIf(_sqs.empty());
}

void findChildren2(const Particle& p, map<long, int>& nRes, int& ncount) const {
  for (const Particle& child : p.children()) {
    if (child.pid() == 443) {
      nRes[child.pid()] += 1;
      ++ncount;
    }
    else if (child.children().empty()) {
      ++nRes[child.pid()];
      ++ncount;
    }
    else {
      findChildren(child, nRes, ncount);
    }
  }
}

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& XX : ufs.particles(Cuts::pid == _pid || Cuts::pid == 20443 || Cuts::pid == 445)) {
    if (XX.children().empty()) continue;
    bool matched = false;
    map<long, int> nRes = nCount;
    int ncount = ntotal;
    findChildren(XX, nRes, ncount);
    for (const Particle& omega : ufs.particles(Cuts::pid == 223)) {
      if (omega.parents()[0].pid() == _pid || omega.children().empty()) continue;
      map<long, int> nRes2 = nRes;
      int ncount2 = ncount;
      findChildren(omega, nRes2, ncount2);
      matched = true;
      for (const auto& val : nRes2) {
        if (val.second != 0) {
          matched = false;
          break;
        }
      }
      if (matched) {
        if (XX.pid() == 20443)
          _h[1]->fill(_sqs);
        else if (XX.pid() == 445)
          _h[2]->fill(_sqs);
        // check decay mode
        else {
          int nOut = 0;
          map<long, int> nDecay;
          findChildren2(XX, nDecay, nOut);
          if (nOut == 3 && nDecay[443] == 1 && nDecay[211] == 1 && nDecay[-211] == 1) _h[0]->fill(_sqs);
        }
        break;
      }
    }
    if (matched) break;
  }
}


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

/// @}


/// @name Histograms
/// @{
int _pid;
BinnedHistoPtr<string> _h[3];
string _sqs = "";
/// @}

};

RIVET_DECLARE_PLUGIN(BESIII_2024_I2779452);

} ```