Rivet analyses

title: BESIII_2017_I1644905

Cross section for $e^+e^-\to\phi\chi_{c(1,2)}$ at $\sqrt{s}=4.600$ GeV

Experiment: BESIII ()

Inspire ID: 1644905

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.D 97 (2018) 3, 032008

Beams: e+ e-

Beam energies: (2.3, 2.3)GeV

Run details: - e+ e- -> hadrons

Measurement of the cross section for $e^+e^-\to\phi\chi_{c(1,2)}$ at $\sqrt{s}=4.600$ GeV.

Source code:BESIII_2017_I1644905.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/FinalState.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief e+ e- -> phi chi_c(1,2) class BESIII_2017_I1644905 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2017_I1644905);


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

/// Book histograms and initialise projections before the run
void init() {
  // projections
  declare(FinalState(), "FS");
  declare(UnstableParticles(), "UFS");
  for (unsigned int ix = 0; ix < 2; ++ix) {
    book(_h[ix], 1, 1, 1 + ix);
  }
}

void findChildren(const Particle& p, map<long, int>& nRes, int& ncount) {
  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");
  // loop over any phi mesons
  for (const Particle& phi : ufs.particles(Cuts::pid == 333)) {
    bool matched = false;
    if (phi.children().empty()) continue;
    map<long, int> nRes = nCount;
    int ncount = ntotal;
    findChildren(phi, nRes, ncount);
    for (const Particle& chi : ufs.particles(Cuts::pid == 20443 || Cuts::pid == 445)) {
      if (chi.children().empty()) continue;
      map<long, int> nRes2 = nRes;
      int ncount2 = ncount;
      findChildren(chi, nRes2, ncount2);
      matched = true;
      for (const auto& val : nRes2) {
        if (val.second != 0) {
          matched = false;
          break;
        }
      }
      if (!matched) continue;
      if (chi.pid() == 20443)
        _h[0]->fill("4.6"s);
      else if (chi.pid() == 445)
        _h[1]->fill("4.6"s);
      break;
    }
    if (matched) break;
  }
}


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

/// @}


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

};

RIVET_DECLARE_PLUGIN(BESIII_2017_I1644905);

} ```