Rivet analyses

title: ARGUS_1987_I248680

$\gamma\gamma\to K^{0}\bar{K}^{0}$ between 1.6 and 3.5 GeV

Experiment: ARGUS (DORIS)

Inspire ID: 248680

Status: VALIDATED

Authors: - Peter Richardson

References: - Eur.Phys.J.C 16 (2000) 435-444

Beams: 22 22

Beam energies: (0.8, 0.8); (0.9, 0.9); (0.9, 0.9); (0.9, 0.9); (1.0, 1.0); (1.0, 1.0); (1.1, 1.1); (1.1, 1.1); (1.1, 1.1); (1.2, 1.2); (1.2, 1.2); (1.3, 1.3); (1.3, 1.3); (1.3, 1.3); (1.4, 1.4); (1.4, 1.4); (1.5, 1.5); (1.5, 1.5); (1.5, 1.5); (1.6, 1.6); (1.6, 1.6); (1.7, 1.7)GeV

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

Measurement of the differential cross section for $\gamma\gamma\to K^{0}\bar{K}^{0}$ for $1.6 \text{GeV} < W < 3.5 \text{GeV}$. The cross section is measured as a function of the centre-of-mass energy of the photonic collision using the $K^+K^-\pi^+\pi^-$ final state.

Source code:ARGUS_1987_I248680.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/FinalState.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief gamma gamma -> K0K0 class ARGUS_1987_I248680 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(ARGUS_1987_I248680);


/// @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 (size_t ih = 0; ih < 5; ++ih) {
    book(_est[ih], 5, 1, ih + 1);
    book(_xsec[ih], "_aux_xsec_" + toString(ih), _est[ih].binning().edges<0>());
  }
  for (double eVal : allowedEnergies()) {
    const string en = toString(round(eVal / MeV));
    if (isCompatibleWithSqrtS(eVal)) _sqs = en;
    for (size_t ix = 0; ix < 9; ++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;
  }
  // find any K* mesons
  int ires = -1;
  const UnstableParticles& ufs = apply<UnstableParticles>(event, "UFS");
  Particles Kstar = ufs.particles(Cuts::abspid == 313);
  for (size_t 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;
    // K*K*
    for (size_t 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) {
        break;
      }
    }
    if (matched) {
      _nMeson[_sqs + "1"s]->fill();
      ires = 7;
      break;
    }
    int sign = Kstar[ix].pid() / Kstar[ix].abspid();
    // three body intermediate states
    if (ncount == 2) {
      // K*0 K- pi+ +ccd
      matched = true;
      for (const auto& val : nRes) {
        if (val.first == sign * 211 || val.first == -sign * 321) {
          if (val.second != 1) {
            matched = false;
            break;
          }
        }
        else {
          if (val.second != 0) {
            matched = false;
            break;
          }
        }
      }
      if (matched) {
        _nMeson[_sqs + "2"s]->fill();
        ires = 6;
        break;
      }
    }
  }
  // look for phi modes
  for (const Particle& p : ufs.particles(Cuts::pid == PID::PHI)) {
    if (p.children().empty()) continue;
    map<long, int> nRes = nCount;
    int ncount = ntotal;
    findChildren(p, nRes, ncount);
    if (ncount == 2) {
      bool matched = true;
      for (const auto& val : nRes) {
        if (abs(val.first) == 211) {
          if (val.second != 1) {
            matched = false;
            break;
          }
        }
        else {
          if (val.second != 0) {
            matched = false;
            break;
          }
        }
      }
      if (matched) {
        ires = 8;
        break;
      }
    }
  }
  // 4 meson modes
  if (ntotal == 4 && nCount[PID::KPLUS] == 1 && nCount[PID::KMINUS] == 1 && nCount[PID::PIPLUS] == 1
      && nCount[PID::PIMINUS] == 1) {
    _nMeson[_sqs + "0"s]->fill();
    _nMeson[_sqs + "4"s]->fill();
    _xsec[0]->fill(sqrtS() / GeV);
    if (ires < 0) {
      _nMeson[_sqs + "3"s]->fill();
      _nMeson[_sqs + "5"s]->fill();
      _xsec[1]->fill(sqrtS() / GeV);
    }
    else {
      _nMeson[_sqs + toString(ires)]->fill();
      if (ires > 3) _xsec[ires - 4]->fill(sqrtS() / GeV);
    }
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  const double sf = crossSection() / nanobarn / sumOfWeights();
  scale(_nMeson, sf);
  scale(_xsec, sf);
  for (size_t ih = 0; ih < 4; ++ih) {
    barchart(_xsec[ih], _est[ih]);
  }
  // loop over tables in paper
  for (size_t ih = 1; ih < 5; ++ih) {
    for (size_t iy = 1; iy < 2; ++iy) {
      string iloc = toString(ih + iy - 2);
      BinnedEstimatePtr<string> mult;
      book(mult, ih, 1, iy);
      for (auto& b : mult->bins()) {
        const double eVal = stod(b.xEdge());
        const string en = toString(round(eVal / MeV));
        b.set(_nMeson[en + iloc]->val(), _nMeson[en + iloc]->err());
      }
    }
  }
}

/// @}


/// @name Histograms
/// @{
map<string, CounterPtr> _nMeson;
Histo1DPtr _xsec[5];
Estimate1DPtr _est[5];
string _sqs = "";
/// @}

};

RIVET_DECLARE_PLUGIN(ARGUS_1987_I248680);

} ```