Rivet analyses

title: SND_2022_I2102082

Cross section for $e^+e^-\to n\bar{n}$ between threshold and 2 GeV

Experiment: SND (VEPP-2M)

Inspire ID: 2102082

Status: VALIDATED

Authors: - Peter Richardson

References: - Eur.Phys.J.C 82 (2022) 8, 761

Beams: e+ e-

Beam energies: (0.9, 0.9); (0.9, 0.9); (1.0, 1.0); (1.0, 1.0); (1.0, 1.0); (1.0, 1.0); (1.0, 1.0); (1.0, 1.0); (1.0, 1.0); (1.0, 1.0); (1.0, 1.0); (1.0, 1.0); (1.0, 1.0); (1.0, 1.0)GeV

Run details: - e+e- to hadrons

Measurement of the cross section for $e^+e^-\to n\bar{n}$ at energies between threshold and 2 GeV.

Source code:SND_2022_I2102082.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/FinalState.hh"

namespace Rivet {

/// @brief e+ e- > n nbar class SND_2022_I2102082 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(SND_2022_I2102082);


/// @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>()) {
    double eval = stod(en) * MeV;
    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() / nanobarn);
}

/// @}


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

};

RIVET_DECLARE_PLUGIN(SND_2022_I2102082); } ```