Rivet analyses

title: SND_2014_I1321689

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

Experiment: SND (VEPP-2M)

Inspire ID: 1321689

Status: VALIDATED

Authors: - Peter Richardson

References: - Phys.Rev. D90 (2014) 112007, 2014

Beams: e+ e-

Beam energies: ANY

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_2014_I1321689.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/FinalState.hh"

namespace Rivet {

/// @brief e+ e- > n nbar class SND_2014_I1321689 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(SND_2014_I1321689);


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

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

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

  // Book histograms
  for (unsigned int ix = 0; ix < 2; ++ix) book(_nneutron[ix], 1 + ix, 1, 1);
}


/// 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;
  }
  for (unsigned int ix = 0; ix < 2; ++ix) _nneutron[ix]->fill(round(sqrtS() / MeV));
}


/// Normalise histograms etc., after the run
void finalize() {

  for (unsigned int ix = 0; ix < 2; ++ix)
    scale(_nneutron[ix], crossSection() / sumOfWeights() / nanobarn);
}

/// @}


/// @name Histograms
/// @{
BinnedHistoPtr<int> _nneutron[2];
/// @}

};

RIVET_DECLARE_PLUGIN(SND_2014_I1321689);

} ```