Rivet analyses

title: ARGUS_1991_I315058

$\gamma\gamma\to \rho^+\rho^-$ between 1.2 and 2.2 GeV

Experiment: ARGUS (DORIS)

Inspire ID: 315058

Status: VALIDATED

Authors: - Peter Richardson

References: - Phys.Lett.B 267 (1991) 535-540

Beams: 22 22

Beam energies: ANY

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

Measurement of the cross section for $\gamma\gamma\to \rho^+\rho^-$ between 1.2 and 2.2 GeV

Source code:ARGUS_1991_I315058.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/FinalState.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief gamma gamma -> rho+ rho- class ARGUS_1991_I315058 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(ARGUS_1991_I315058);


/// @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
  if (inRange(sqrtS() / GeV, 1.2, 2.2)) {
    for (unsigned int ix = 0; ix < 3; ++ix) {
      book(_c[ix], "TMP/nMeson_" + toString(ix + 1));
    }
  }
  else {
    throw Error("Invalid CMS energy for ARGUS_1991_I315058");
  }
}

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");
  // find the final-state particles
  map<long, int> nCount;
  int ntotal(0);
  for (const Particle& p : fs.particles()) {
    nCount[p.pid()] += 1;
    ++ntotal;
  }
  bool foundRes = false;
  // find any rho mesons
  Particles rho = apply<UnstableParticles>(event, "UFS").particles(Cuts::abspid == 213);
  for (unsigned int ix = 0; ix < rho.size(); ++ix) {
    if (rho[ix].children().empty()) continue;
    map<long, int> nRes = nCount;
    int ncount = ntotal;
    findChildren(rho[ix], nRes, ncount);
    bool matched = false;
    for (unsigned int iy = ix + 1; iy < rho.size(); ++iy) {
      if (rho[iy].children().empty()) continue;
      if (rho[ix].pid() != -rho[iy].pid()) continue;
      map<long, int> nRes2 = nRes;
      int ncount2 = ncount;
      findChildren(rho[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) {
      _c[0]->fill();
      foundRes = true;
      break;
    }
    else {
      int sign = rho[ix].pid() / rho[ix].abspid();
      bool matched2 = true;
      for (const auto& val : nRes) {
        if (val.first == -sign * 211 || val.first == 111) {
          if (val.second != 1) {
            matched2 = false;
            break;
          }
        }
        else {
          if (val.second != 0) {
            matched2 = false;
            break;
          }
        }
      }
      if (matched2) {
        _c[1]->fill();
        foundRes = true;
        break;
      }
    }
  }
  // 4 pion final-state
  if (ntotal == 4) {
    if (nCount[PID::PIPLUS] == 1 && nCount[PID::PIMINUS] == 1 && nCount[PID::PI0] == 2) {
      if (!foundRes) _c[2]->fill();
    }
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  scale(_c, crossSection() / nanobarn / sumOfWeights());
  // loop over tables in paper
  for (unsigned int ix = 0; ix < 3; ++ix) {
    Estimate1DPtr mult;
    book(mult, 1, 1, 1 + ix);
    for (auto& b : mult->bins()) {
      if (inRange(sqrtS(), b.xMin(), b.xMax())) {
        b.set(_c[ix]->val(), _c[ix]->err());
      }
    }
  }
}

/// @}


/// @name Histograms
/// @{
CounterPtr _c[3];
/// @}

};

RIVET_DECLARE_PLUGIN(ARGUS_1991_I315058);

} ```