Rivet analyses

title: CMD2_2000_I511375

Cross section for $e^+e^-\to\pi^+\pi^+\pi^-\pi^+$ below 1 GeV

Experiment: CMD2 (VEPP-2M)

Inspire ID: 511375

Status: VALIDATED

Authors: - Peter Richardson

References: - Phys.Lett. B475 (2000) 190-197, 2000

Beams: e+ e-

Beam energies: ANY

Run details: - e+e- to hadrons

Measurement of the cross section for $e^+e^-\to\pi^+\pi^+\pi^-\pi^+$ below 1 GeV

Source code:CMD2_2000_I511375.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/FinalState.hh"

namespace Rivet {

/// @brief e+e- > pi+pi- class CMD2_2000_I511375 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(CMD2_2000_I511375);


/// @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>()) {
    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() / GeV, emin, emax)) {
        _sqs = en;
        break;
      }
    }
    else {
      const 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() != 4) 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(CMD2_2000_I511375); } ```