Rivet analyses

title: SND_2020_I1806118

Cross Section for $e^+e^-\to K^+K^-\pi^0$ and $\phi\pi^0$ from threshold to 2.1 GeV

Experiment: SND (VEPP-2000)

Inspire ID: 1806118

Status: VALIDATED

Authors: - Peter Richardson

References: - arXiv: 2006.05465

Beams: e+ e-

Beam energies: ANY

Run details: - e+ e- to hadrons

Cross section for $e^+e^-\to K^+K^-\pi^0$ between threshold and 2.1 GeV. The $\phi\pi^0$ radiative subprocess is also measured.

Source code:SND_2020_I1806118.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/FinalState.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief e+e- -> K+K-pi0 class SND_2020_I1806118 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(SND_2020_I1806118);


/// @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(_nKKPi, 1, 1, 1);
  book(_nPhiPi, "TMP/nPhiPi", refData(2, 1, 1));
  for (const string& en : _nKKPi.binning().edges<0>()) {
    double end = stod(en) * GeV;
    if (isCompatibleWithSqrtS(end, 5e-3)) {
      _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;
  }
  if (ntotal == 3 && nCount[321] == 1 && nCount[-321] == 1 && nCount[111] == 1) {
    // KK pi state
    _nKKPi->fill(_sqs);
  }
  // phi pi state
  const FinalState& ufs = apply<FinalState>(event, "UFS");
  for (const Particle& p : ufs.particles(Cuts::pid == 333)) {
    if (p.children().empty()) continue;
    map<long, int> nRes = nCount;
    int ncount = ntotal;
    findChildren(p, nRes, ncount);
    if (ncount != 1) continue;
    bool matched = true;
    for (const auto& val : nRes) {
      if (val.first == 111) {
        if (val.second != 1) {
          matched = false;
          break;
        }
      }
      else if (val.second != 0) {
        matched = false;
        break;
      }
    }
    if (matched) {
      _nPhiPi->fill(sqrtS() / GeV);
      break;
    }
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  double fact = crossSection() / sumOfWeights() / nanobarn;
  scale(_nKKPi, fact);
  scale(_nPhiPi, fact);
  Estimate1DPtr mult;
  book(mult, 2, 1, 1);
  barchart(_nPhiPi, mult);
}
/// @}


/// @name Histograms
/// @{
BinnedHistoPtr<string> _nKKPi;
Histo1DPtr _nPhiPi;
string _sqs = "";
/// @}

};

RIVET_DECLARE_PLUGIN(SND_2020_I1806118); } ```