Rivet analyses

e⁺e⁻ → e⁺e⁻η^′ via intermediate photons at 10.58 GeV

Experiment: BABAR (PEP-II)

Inspire ID: 1691222

Status: VALIDATED

Authors: - Peter Richardson

References: - Phys.Rev.D 98 (2018) 11, 112002

Beams: e+ e-

Beam energies: (5.3, 5.3)GeV

Run details: - e+ e- > e+e- meson via photon photon -> meson

Measurement of the cross section for the production of η^′ in photon-photon collisions, i.e. e⁺e⁻ → γγe⁺e⁻ followed by γγ → η^′, by the Babar experiment at 10.58 GeV. This measurement is doubly differential in the virtuality of the two photons.

Source code:`BABAR_2018_I1691222.cc`

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

namespace Rivet {


  /// @brief e+e- > e+e- eta'
  class BABAR_2018_I1691222 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BABAR_2018_I1691222);


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

    /// Book histograms and initialise projections before the run
    void init() {
      // Initialise and register projections
      declare(Beam(), "Beams");
      declare(FinalState(), "FS");
      declare(UnstableParticles(), "UFS");
      // book the histograms
      book(_h_etap, 1, 1, 1);
    }

    void findChildren(const Particle& p, map<long, int>& nRes, int& ncount) {
      for (const Particle& child : p.children()) {
        if (child.children().empty()) {
          --nRes[child.pid()];
          --ncount;
        }
        else {
          findChildren(child, nRes, ncount);
        }
      }
    }

    bool findScattered(Particle beam, double& q2) {
      bool found = false;
      Particle scat = beam;
      while (!scat.children().empty()) {
        found = false;
        for (const Particle& p : scat.children()) {
          if (p.pid() == scat.pid()) {
            scat = p;
            found = true;
            break;
          }
        }
        if (!found) break;
      }
      if (!found) return false;
      q2 = -(beam.momentum() - scat.momentum()).mass2();
      return true;
    }

    /// Perform the per-event analysis
    void analyze(const Event& event) {
      if (_edges.empty()) _edges = _h_etap->xEdges();
      // find scattered leptons and calc Q2
      const Beam& beams = apply<Beam>(event, "Beams");
      double q12 = -1, q22 = -1;
      if (!findScattered(beams.beams().first, q12)) vetoEvent;
      if (!findScattered(beams.beams().second, q22)) vetoEvent;
      if (q22 > q12) swap(q12, q22);
      // check the final state
      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;
      }
      // find the meson
      const FinalState& ufs = apply<FinalState>(event, "UFS");
      for (const Particle& p : ufs.particles(Cuts::pid == 331)) {
        if (p.children().empty()) continue;
        map<long, int> nRes = nCount;
        int ncount = ntotal;
        findChildren(p, nRes, ncount);
        bool matched = true;
        for (const auto& val : nRes) {
          if (abs(val.first) == 11) {
            if (val.second != 1) {
              matched = false;
              break;
            }
          }
          else if (val.second != 0) {
            matched = false;
            break;
          }
        }
        if (matched) {
          // 2<Q2<10 for both photons bin
          if (q12 > 2. && q12 < 10. && q22 > 2. && q22 < 10.) {
            _h_etap->fill(_edges[0], 1. / sqr(8.));
          }
          // 10<Q2<30 for both photons bin
          else if (q12 > 10 && q12 < 30. && q22 > 10. && q22 < 30.)
            _h_etap->fill(_edges[1], 1. / sqr(20.));
          // 10<Q12<30 2<Q22<10
          else if (q22 > 2. && q22 < 10. && q12 > 10. && q12 < 30.)
            _h_etap->fill(_edges[2], 1. / 8. / 20. / 2.);
          // 2<Q22<30 30<Q12<60
          else if (q22 > 2. && q22 < 30. && q12 > 30. && q12 < 60.)
            _h_etap->fill(_edges[3], 1. / 28. / 30. / 2.);
          // 30<Q2<60 for both photons
          else if (q22 > 30. && q22 < 60. && q12 > 30. && q12 < 60.)
            _h_etap->fill(_edges[4], 1. / sqr(30.));
        }
      }
    }

    /// Normalise histograms etc., after the run
    void finalize() {
      scale(_h_etap, 1e4 * crossSection() / femtobarn / sumW());
    }

    ///@}


    /// @name Histograms
    ///@{
    BinnedHistoPtr<string> _h_etap;
    vector<string> _edges;
    ///@}
  };


  RIVET_DECLARE_PLUGIN(BABAR_2018_I1691222);

}

Rivet analyses

e+e− → e+e−η′ via intermediate photons at 10.58 GeV

Source code:BABAR_2018_I1691222.cc

e⁺e⁻ → e⁺e⁻η^′ via intermediate photons at 10.58 GeV

Source code:`BABAR_2018_I1691222.cc`