Rivet analyses

γγ → ρ+ρ− between 0.8 and 3.4 GeV

Experiment: ARGUS (DORIS)

Inspire ID: 266416

Status: VALIDATED

Authors: - Peter Richardson

References: - Phys.Lett.B 217 (1989) 205-210

Beams: 22 22

Beam energies: (0.4, 0.4); (0.5, 0.5); (0.5, 0.5); (0.6, 0.6); (0.6, 0.6); (0.7, 0.7); (0.7, 0.7); (0.7, 0.7); (0.8, 0.8); (0.8, 0.8); (0.8, 0.8); (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); (1.1, 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); (1.6, 1.6); (1.6, 1.6); (1.7, 1.7)GeV

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

Measurement of the differential cross section for γγ → ρ+ρ− for 0.8GeV < W < 3.4GeV. The cross section is measured as a function of the centre-of-mass energy of the photonic collision using the π+π−π0π0 final state.

Source code:ARGUS_1989_I266416.cc

// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/FinalState.hh"
#include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {


  /// @brief gamma gamma -> rho+ rho-
  class ARGUS_1989_I266416 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(ARGUS_1989_I266416);


    /// @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 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 (size_t 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) {
          _nMeson[_sqs + "1"s]->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) {
            _nMeson[_sqs + "2"s]->fill();
            foundRes = true;
            break;
          }
        }
      }
      // 4 pion final-state
      if (ntotal == 4) {
        if (nCount[PID::PIPLUS] == 1 && nCount[PID::PIMINUS] == 1 && nCount[PID::PI0] == 2) {
          _nMeson[_sqs + "0"s]->fill();
          if (!foundRes) _nMeson[_sqs + "3"]->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_1989_I266416);

}