Rivet analyses

title: CMD3_2013_I1217420

Cross section for $e^+e^-\to3(\pi^+\pi^-)$ below 2 GeV by CMD3

Experiment: CMD3 (VEPP-2M)

Inspire ID: 1217420

Status: VALIDATED

Authors: - Peter Richardson

References: - arXiv: 1302.0053

Beams: e+ e-

Beam energies: ANY

Run details: - e+ e- to hadrons

Measurement of the cross section for $e^+e^-\to3(\pi^+\pi^-)$ for energies below 2 GeV by the CMD3 experiment

Source code:CMD3_2013_I1217420.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/FinalState.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief e+e- -> 3(pi+pi-) class CMD3_2013_I1217420 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(CMD3_2013_I1217420);


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

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

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

  // Book histograms
  for (unsigned int ix = 0; ix < 3; ++ix) book(_sigma[ix], 1, 1, 1 + ix);
}

void findChildren(const Particle& p, map<long, int>& nRes, int& ncount) {
  for (const Particle& child : p.children()) {
    if (child.children().empty()) {
      --nRes[child.pid()];
      --ncount;
    }
    else
      findChildren(child, nRes, ncount);
  }
}

/// Perform the per-event analysis
void analyze(const Event& event) {
  // find the final-state particles
  const FinalState& fs = apply<FinalState>(event, "FS");
  map<long, int> nCount;
  int ntotal(0);
  for (const Particle& p : fs.particles()) {
    nCount[p.pid()] += 1;
    ++ntotal;
  }
  if (ntotal == 6 && nCount[211] == 3 && nCount[-211] == 3) {
    for (unsigned int ix = 0; ix < 3; ++ix) _sigma[ix]->fill(round(sqrtS() / MeV));
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  double fact = crossSection() / nanobarn / sumOfWeights();
  for (unsigned int ix = 0; ix < 3; ++ix) scale(_sigma[ix], fact);
}

/// @}


/// @name Histograms
/// @{
BinnedHistoPtr<int> _sigma[3];
/// @}

};

RIVET_DECLARE_PLUGIN(CMD3_2013_I1217420);

} ```