Rivet analyses

title: BELLE_2022_I2146263

Cross section for $e^+e^-\to\eta\phi$

Experiment: BELLE (KEKB)

Inspire ID: 2146263

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.D 107 (2023) 012006 - arXiv: 2209.00810

Beams: e+ e-

Beam energies: ANY

Run details: - e+ e- to hadrons

Measurement of the cross section for $e^+e^-\to\eta\phi$ using ISR for centre-of-mass energies between 1.55 and 3.95 GeV by the BELLE collaboration.

Source code:BELLE_2022_I2146263.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/FinalState.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief e+ e- > eta phi class BELLE_2022_I2146263 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BELLE_2022_I2146263);


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

/// Book histograms and initialise projections before the run
void init() {

  // Initialise and register projections
  declare(FinalState(), "FS");
  declare(UnstableParticles(), "UFS");
  book(_sigmaPhiEta, "/TMP/_nPhiEta", refData(1, 1, 1));
}

void findChildren(const Particle& p, map<long, int>& nRes, int& ncount) {
  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");

  // loop over eta mesons
  for (const Particle& p : ufs.particles(Cuts::pid == 221)) {
    if (p.children().empty()) continue;
    map<long, int> nRes = nCount;
    int ncount = ntotal;
    findChildren(p, nRes, ncount);
    // loop over phi mesons
    for (const Particle& p2 : ufs.particles(Cuts::pid == 333)) {
      if (p2.parents()[0].isSame(p)) continue;
      map<long, int> nResB = nRes;
      int ncountB = ncount;
      findChildren(p2, nResB, ncountB);
      if (ncountB != 0) continue;
      bool matched = true;
      for (const auto& val : nResB) {
        if (val.second != 0) {
          matched = false;
          break;
        }
      }
      if (matched) _sigmaPhiEta->fill(sqrtS());
    }
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  scale(_sigmaPhiEta, crossSection() / sumOfWeights() / picobarn);
  Estimate1DPtr tmp;
  book(tmp, 1, 1, 1);
  barchart(_sigmaPhiEta, tmp);
}

/// @}


/// @name Histograms
/// @{
Histo1DPtr _sigmaPhiEta;
/// @}

};

RIVET_DECLARE_PLUGIN(BELLE_2022_I2146263);

} ```