Rivet analyses

title: DM2_1989_I267118

Cross section for $e^+e^-\to \pi^+\pi^-$ between 1.35 and 2.4 GeV

Experiment: DM2 (DCI)

Inspire ID: 267118

Status: VALIDATED

Authors: - Peter Richardson

References: - Phys.Lett. B220 (1989) 321-327, 1989

Beams: e+ e-

Beam energies: (0.7, 0.7); (0.7, 0.7); (0.7, 0.7); (0.7, 0.7); (0.8, 0.8); (0.8, 0.8); (0.8, 0.8); (0.8, 0.8); (0.9, 0.9); (0.9, 0.9); (0.9, 0.9); (0.9, 0.9); (1.0, 1.0); (1.0, 1.0); (1.0, 1.0); (1.0, 1.0); (1.1, 1.1)GeV

Run details: - e+ e- to hadrons

Measurement of the cross section for $e^+e^-\to \pi^+\pi^-$ at energies between 1.35 and 2.4 GeV. Useful for comparing models of the pion form factor.

Source code:DM2_1989_I267118.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/FinalState.hh"

namespace Rivet {

/// @brief e+e- > pi+pi- class DM2_1989_I267118 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(DM2_1989_I267118);


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

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

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

  // Book histograms
  book(_npion, 1, 1, 1);
  for (const string& en : _npion.binning().edges<0>()) {
    double eval = stod(en) * GeV;
    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");
  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<string> _npion;
string _sqs = "";
/// @}

};

RIVET_DECLARE_PLUGIN(DM2_1989_I267118); } ```