Rivet Analyses Reference

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

Source code: SND_2014_I1321689.cc
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// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/FinalState.hh"


namespace Rivet {


  /// @brief Add a short analysis description here
  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
      book(_nneutron, "TMP/neutron");

    }


    /// 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(abs(p.pid())!=PID::NEUTRON) vetoEvent;
      }
      _nneutron->fill();
    }


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

      double sigma = _nneutron->val();
      double error = _nneutron->err();
      sigma *= crossSection()/ sumOfWeights() /nanobarn;
      error *= crossSection()/ sumOfWeights() /nanobarn;
      for(unsigned int ix=1;ix<3;++ix) {
	Scatter2D temphisto(refData(ix, 1, 1));
	Scatter2DPtr mult;
	book(mult, ix, 1, 1);
	for (size_t b = 0; b < temphisto.numPoints(); b++) {
	  const double x  = temphisto.point(b).x();
	  pair<double,double> ex = temphisto.point(b).xErrs();
	  pair<double,double> ex2 = ex;
	  if(ex2.first ==0.) ex2. first=0.0001;
	  if(ex2.second==0.) ex2.second=0.0001;
	  if (inRange(sqrtS()/MeV, x-ex2.first, x+ex2.second)) {
	    mult->addPoint(x, sigma, ex, make_pair(error,error));
	  }
	  else {
	    mult->addPoint(x, 0., ex, make_pair(0.,.0));
	  }
	}
      }

    }

    //@}


    /// @name Histograms
    //@{
    CounterPtr _nneutron;
    //@}


  };


  // The hook for the plugin system
  RIVET_DECLARE_PLUGIN(SND_2014_I1321689);


}