Rivet analyses

title: ARGUS_1988_I262713

$\gamma\gamma\to K^{+}K^{-}$ between 1.6 and 2.6 GeV

Experiment: ARGUS (DORIS)

Inspire ID: 262713

Status: VALIDATED

Authors: - Peter Richardson

References: - Phys.Lett.B 212 (1988) 528-532, 1988

Beams: 22 22

Beam energies: (0.8, 0.8); (0.9, 0.9); (0.9, 0.9); (1.1, 1.1); (1.1, 1.1); (1.1, 1.1); (1.2, 1.2); (1.4, 1.4); (1.4, 1.4)GeV

Run details: - gamma gamma to hadrons, K0S and pi0 mesons must be set stable

Measurement of the differential cross section for $\gamma\gamma\to K^{+}K^{-}$ for $1.4 \text{GeV} < W < 2.6 \text{GeV}$. The cross section is measured as a function of the centre-of-mass energy of the photonic collision using the $2K^0_S\pi^+\pi^-$ and $K^0_SK^-\pi^0\pi^+$+c.c final states.

Source code:ARGUS_1988_I262713.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/FinalState.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief gamma gamma -> K+K- class ARGUS_1988_I262713 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(ARGUS_1988_I262713);


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

/// Book histograms and initialise projections before the run
void init() {
  // Initialise and register projections
  declare(FinalState(), "FS");
  declare(UnstableParticles(), "UFS");
  // book histos
  for (double eVal : allowedEnergies()) {
    const string en = toString(round(eVal / MeV));
    if (isCompatibleWithSqrtS(eVal)) _sqs = en;
    for (size_t ix = 0; ix < 4; ++ix) {
      book(_nMeson[en + toString(ix)], "TMP/nMeson_" + en + "_" + toString(ix + 1));
    }
  }
  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");
  // find the final-state particles
  map<long, int> nCount;
  int ntotal(0);
  for (const Particle& p : fs.particles()) {
    nCount[p.pid()] += 1;
    ++ntotal;
  }
  bool resonant = false;
  // find any K* mesons
  Particles Kstar = apply<UnstableParticles>(event, "UFS").particles(Cuts::abspid == 323);
  for (unsigned int ix = 0; ix < Kstar.size(); ++ix) {
    if (Kstar[ix].children().empty()) continue;
    map<long, int> nRes = nCount;
    int ncount = ntotal;
    findChildren(Kstar[ix], nRes, ncount);
    bool matched = false;
    for (unsigned int iy = ix + 1; iy < Kstar.size(); ++iy) {
      if (Kstar[iy].children().empty()) continue;
      if (Kstar[ix].pid() != -Kstar[iy].pid()) continue;
      map<long, int> nRes2 = nRes;
      int ncount2 = ncount;
      findChildren(Kstar[iy], nRes2, ncount2);
      if (ncount2 != 0) continue;
      matched = true;
      for (const auto& val : nRes2) {
        if (val.second != 0) {
          matched = false;
          break;
        }
      }
      if (matched) {
        _nMeson[_sqs + "0"s]->fill();
        resonant = true;
        break;
      }
    }
    if (matched) break;
  }
  // 4 meson final state
  if (ntotal == 4) {
    if (nCount[PID::K0S] == 2 && nCount[PID::PIPLUS] == 1 && nCount[PID::PIMINUS] == 1) {
      _nMeson[_sqs + "1"s]->fill();
    }
    else if (nCount[PID::K0S] == 1 && nCount[PID::PI0] == 1
             && ((nCount[PID::KPLUS] == 1 && nCount[PID::PIMINUS] == 1)
                 || (nCount[PID::KMINUS] == 1 && nCount[PID::PIPLUS] == 1))) {
      _nMeson[_sqs + "2"s]->fill();
      if (!resonant) _nMeson[_sqs + "3"s]->fill();
    }
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  scale(_nMeson, crossSection() / nanobarn / sumOfWeights());
  // loop over tables in paper
  for (size_t ix = 0; ix < 4; ++ix) {
    BinnedEstimatePtr<string> mult;
    book(mult, ix + 1, 1, 1);
    for (auto& b : mult->bins()) {
      const double eVal = std::stod(b.xEdge());
      const string en = toString(round(eVal / MeV));
      b.set(_nMeson[en + toString(ix)]->val(), _nMeson[en + toString(ix)]->err());
    }
  }
}

/// @}


/// @name Histograms
/// @{
map<string, CounterPtr> _nMeson;
string _sqs = "";
/// @}

};

RIVET_DECLARE_PLUGIN(ARGUS_1988_I262713);

} ```