Rivet analyses

Cross section for e+e−→ neutron and antineutron between 2. and 3.08 GeV

Experiment: BESIII (BEPC II)

Inspire ID: 1966612

Status: VALIDATED

Authors: - Peter Richardson

References: - Nature Phys. 17 (2021) 11, 1200-1204

Beams: e+ e-

Beam energies: (1.0, 1.0); (1.0, 1.0); (1.1, 1.1); (1.1, 1.1); (1.1, 1.1); (1.1, 1.1); (1.1, 1.1); (1.1, 1.1); (1.2, 1.2); (1.2, 1.2); (1.2, 1.2); (1.3, 1.3); (1.4, 1.4); (1.5, 1.5); (1.5, 1.5); (1.5, 1.5); (1.5, 1.5); (1.5, 1.5)GeV

Run details: - e+ e- to hadrons

Measurement of the cross section for e+e− → pp̄ for energies between 2. and 3.08 GeV.

Source code:BESIII_2021_I1966612.cc

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

namespace Rivet {


  /// @brief e+ e- > n nbar
  class BESIII_2021_I1966612 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2021_I1966612);


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

    /// Book histograms and initialise projections before the run
    void init() {

      // Initialise and register projections
      declare(FinalState(), "FS");

      // Book histograms
      book(_nneutron, 1, 1, 1);

      for (const string& en : _nneutron.binning().edges<0>()) {
        const double eval = stod(en)*GeV;
        if (isCompatibleWithSqrtS(eval)) {
          _sqs = en; break;
        }
      }
      raiseBeamErrorIf(_sqs.empty());
    }


    /// Perform the per-event analysis
    void analyze(const Event& event) {
      const FinalState& fs = apply<FinalState>(event, "FS");
      if (fs.particles().size()!=2) vetoEvent;
      for (const Particle& p :  fs.particles()) {
        if (p.abspid()!=PID::NEUTRON) vetoEvent;
      }
      _nneutron->fill(_sqs);
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      scale(_nneutron, crossSection()/ sumOfWeights() /picobarn);
    }

    ///@}


    /// @name Histograms
    ///@{
    BinnedHistoPtr<string> _nneutron;
    string _sqs = "";
    ///@}


  };


  RIVET_DECLARE_PLUGIN(BESIII_2021_I1966612);

}