Rivet analyses

title: CMD2_2007_I728302

Cross section for $e^+e^-\to \pi^+\pi^-$ between 600 and 970 MeV

Experiment: CMD2 (VEPP-2M)

Inspire ID: 728302

Status: VALIDATED

Authors: - Peter Richardson

References: - Phys.Lett. B648 (2007) 28-38, 2007

Beams: e+ e-

Beam energies: (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); (0.5, 0.5); (0.5, 0.5); (0.5, 0.5); (0.5, 0.5); (0.5, 0.5)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 600 and 970 MeV. Useful for comparing models of the pion form factor.

Source code:CMD2_2007_I728302.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/FinalState.hh"

namespace Rivet {

/// @brief Add a short analysis description here class CMD2_2007_I728302 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(CMD2_2007_I728302);


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

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

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

  // Book histograms
  book(_npion, 2, 1, 1);
  for (double en : allowedEnergies()) {
    if (isCompatibleWithSqrtS(en)) {
      _sqs = round(en / MeV);
      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_2007_I728302); } ```