Rivet analyses

title: BABAR_2009_I829441

Cross section for $e^+e^-\to \pi^+\pi^-$ below 3 GeV

Experiment: BABAR (PEP-II)

Inspire ID: 829441

Status: VALIDATED

Authors: - Peter Richardson

References: - Phys.Rev.Lett. 103 (2009) 231801 - Phys.Rev. D86 (2012) 032013

Beams: e+ e-

Beam energies: ANY

Run details: - e+e- to hadrons

Source code:BABAR_2009_I829441.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/FinalState.hh"

namespace Rivet {

/// @brief Add a short analysis description here class BABAR_2009_I829441 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BABAR_2009_I829441);


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

/// Book histograms and initialise projections before the run
void init() {
  // Initialise and register projections
  declare(FinalState(), "FS");

  // Book histograms
  book(_npion, "TMP/pion");
}


/// 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 (abs(p.pid()) != PID::PIPLUS) vetoEvent;
  }
  _npion->fill();
}


/// Normalise histograms etc., after the run
void finalize() {
  double sigma = _npion->val();
  double error = _npion->err();
  sigma *= crossSection() / sumOfWeights() / nanobarn;
  error *= crossSection() / sumOfWeights() / nanobarn;
  Estimate1DPtr mult;
  book(mult, 1, 1, 1);
  for (auto& b : mult->bins()) {
    if (inRange(sqrtS() / GeV, b.xMin(), b.xMax())) {
      b.set(sigma, error);
    }
  }
}

/// @}


/// @name Histograms
/// @{
CounterPtr _npion;
/// @}

};

RIVET_DECLARE_PLUGIN(BABAR_2009_I829441);

} ```