Rivet analyses

title: SND_2016_I1418483

Cross section for $e^+e^-\to\pi\gamma$ for energies between 600 MeV and 1380 MeV

Experiment: SND (VEPP-2M)

Inspire ID: 1418483

Status: VALIDATED

Authors: - Peter Richardson

References: - Phys.Rev. D93 (2016) no.9, 092001

Beams: e+ e-

Beam energies: ANY

Run details: - e+ e- to hadrons

Cross section for $e^+e^-\to\pi\gamma$ for energies between 600 MeV and 1380 MeV

Source code:SND_2016_I1418483.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/FinalState.hh"

namespace Rivet {

/// @brief e+e- -> pi0 gamma class SND_2016_I1418483 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(SND_2016_I1418483);


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

/// Book histograms and initialise projections before the run
void init() {
  declare(FinalState(), "FS");
  book(_numPi0Gamma, 1, 1, 5);
  for (const string& en : _numPi0Gamma.binning().edges<0>()) {
    const size_t idx = en.find("-");
    if (idx != string::npos) {
      const double emin = stod(en.substr(0, idx));
      const double emax = stod(en.substr(idx + 1, string::npos));
      if (inRange(sqrtS() / MeV, emin, emax)) {
        _sqs = en;
        break;
      }
    }
    else {
      const 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");

  map<long, int> nCount;
  int ntotal(0);
  for (const Particle& p : fs.particles()) {
    nCount[p.pid()] += 1;
    ++ntotal;
  }
  if (ntotal == 2 && nCount[22] == 1 && nCount[111] == 1) {
    _numPi0Gamma->fill(_sqs);
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  scale(_numPi0Gamma, crossSection() / sumOfWeights() / nanobarn);
}

/// @}


/// @name Histograms
/// @{
BinnedHistoPtr<string> _numPi0Gamma;
string _sqs = "";
/// @}

};

RIVET_DECLARE_PLUGIN(SND_2016_I1418483);

} ```