Rivet analyses

title: CMD_1985_I221309

Cross section for $e^+e^-\to \pi^+\pi^-$ for energies below 1.4 GeV

Experiment: CMD (VEPP-2M)

Inspire ID: 221309

Status: VALIDATED

Authors: - Peter Richardson

References: - Nucl.Phys. B256 (1985) 365-384, 1985

Beams: e+ e-

Beam energies: (0.2, 0.2); (0.2, 0.2); (0.2, 0.2); (0.2, 0.2); (0.2, 0.2); (0.2, 0.2); (0.2, 0.2); (0.2, 0.2); (0.3, 0.3); (0.3, 0.3); (0.3, 0.3); (0.3, 0.3); (0.3, 0.3); (0.3, 0.3); (0.3, 0.3); (0.3, 0.3); (0.3, 0.3); (0.3, 0.3); (0.3, 0.3); (0.4, 0.4); (0.4, 0.4); (0.4, 0.4); (0.4, 0.4); (0.4, 0.4); (0.4, 0.4); (0.4, 0.4); (0.4, 0.4); (0.4, 0.4); (0.4, 0.4); (0.4, 0.4); (0.4, 0.4); (0.4, 0.4); (0.4, 0.4); (0.4, 0.4); (0.4, 0.4); (0.4, 0.4); (0.4, 0.4); (0.4, 0.4); (0.4, 0.4); (0.4, 0.4); (0.4, 0.4); (0.4, 0.4); (0.4, 0.4); (0.4, 0.4); (0.4, 0.4); (0.4, 0.4); (0.4, 0.4); (0.4, 0.4); (0.4, 0.4); (0.4, 0.4); (0.4, 0.4); (0.4, 0.4); (0.4, 0.4); (0.4, 0.4); (0.4, 0.4); (0.4, 0.4); (0.4, 0.4); (0.4, 0.4); (0.4, 0.4); (0.5, 0.5); (0.5, 0.5); (0.5, 0.5); (0.5, 0.5); (0.5, 0.5); (0.5, 0.5); (0.5, 0.5); (0.5, 0.5); (0.5, 0.5); (0.5, 0.5); (0.5, 0.5); (0.5, 0.5); (0.5, 0.5); (0.5, 0.5); (0.5, 0.5); (0.6, 0.6); (0.6, 0.6); (0.6, 0.6); (0.6, 0.6); (0.6, 0.6); (0.6, 0.6); (0.6, 0.6); (0.6, 0.6); (0.6, 0.6); (0.6, 0.6); (0.6, 0.6); (0.6, 0.6); (0.6, 0.6); (0.6, 0.6); (0.6, 0.6); (0.6, 0.6); (0.6, 0.6); (0.6, 0.6); (0.6, 0.6); (0.7, 0.7); (0.7, 0.7); (0.7, 0.7); (0.7, 0.7); (0.7, 0.7); (0.7, 0.7); (0.7, 0.7); (0.7, 0.7); (0.7, 0.7); (0.7, 0.7)GeV

Run details: - e+e- to hadrons

Measurement of the cross section for $e^+e^-\to \pi^+\pi^-$ at energies below 1.4 GeV.

Source code:CMD_1985_I221309.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/FinalState.hh"

namespace Rivet {

/// @brief e+e- -> pi+pi- class CMD_1985_I221309 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(CMD_1985_I221309);


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

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

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

  // Book histograms
  book(_sigma1, 1, 1, 1);
  book(_sigma2, 2, 1, 1);
  for (const string& en : _sigma1.binning().edges<0>()) {
    double eval = stod(en) * MeV;
    if (isCompatibleWithSqrtS(eval)) {
      _sqs = en;
      break;
    }
  }
  for (int en : _sigma2.binning().edges<0>()) {
    double eval = en * MeV;
    if (isCompatibleWithSqrtS(eval)) {
      _isqs = en;
      break;
    }
  }
  raiseBeamErrorIf(_sqs.empty() && _isqs < 0.);
}


/// 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::PIPLUS) vetoEvent;
  }
  if (!_sqs.empty()) _sigma1->fill(_sqs);
  if (_isqs > 0) _sigma2->fill(_isqs);
}


/// Normalise histograms etc., after the run
void finalize() {
  scale(_sigma1, crossSection() / sumOfWeights() / nanobarn);
  scale(_sigma2, crossSection() / sumOfWeights() / nanobarn);
}

/// @}


/// @name Histograms
/// @{
BinnedHistoPtr<string> _sigma1;
BinnedHistoPtr<int> _sigma2;
string _sqs = "";
int _isqs = -1;
/// @}

};

RIVET_DECLARE_PLUGIN(CMD_1985_I221309); } ```