Rivet analyses

title: CMD2_2006_I728191

Cross section for $e^+e^-\to \pi^+\pi^-$ between 370 and 520 MeV

Experiment: CMD2 (VEPP-2M)

Inspire ID: 728191

Status: VALIDATED

Authors: - Peter Richardson

References: - JETP Lett. 84 (2006) 413-417, 2006

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)GeV

Run details: - e+ e- to hadrons below 0.6 and 0.9 GeV

Measurement of the cross section for $e^+e^-\to \pi^+\pi^-$ at energies between 370 and 520 MeV. Useful for comparing models of the pion form factor.

Source code:CMD2_2006_I728191.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/FinalState.hh"

namespace Rivet {

/// @brief Add a short analysis description here class CMD2_2006_I728191 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(CMD2_2006_I728191);


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

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

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

  // Book histograms
  book(_npion, 3, 1, 1);
  for (double eVal : allowedEnergies()) {
    int en = round(eVal / MeV);
    if (isCompatibleWithSqrtS(eVal)) {
      _sqs = en;
      break;
    }
  }
  raiseBeamErrorIf(_sqs < 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;
  }
  _npion->fill(_sqs);
}


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

/// @}


/// @name Histograms
/// @{
BinnedHistoPtr<int> _npion;
int _sqs = -1;
/// @}

};

RIVET_DECLARE_PLUGIN(CMD2_2006_I728191); } ```