Rivet analyses

title: PLUTO_1984_I204487

$\gamma\gamma\to\pi^+\pi^-$ for centre-of-mass energies between 0.36 and 1.72 GeV

Experiment: PLUTO (PETRA)

Inspire ID: 204487

Status: VALIDATED

Authors: - Peter Richardson

References: - Z.Phys.C 26 (1984) 199, 1984

Beams: 22 22

Beam energies: ANY

Run details: - gamma gamma to hadrons

Measurement of the differential cross section for $\gamma\gamma\to\pi^+\pi^-$. The cross section as a function of the centre-of-mass energy of the photonic collision is measured.

Source code:PLUTO_1984_I204487.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/FinalState.hh"

namespace Rivet {

/// @brief gamma gamma -> pi+pi- class PLUTO_1984_I204487 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(PLUTO_1984_I204487);


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

/// Book histograms and initialise projections before the run
void init() {
  // Final state
  declare(FinalState(), "FS");
  // check CMS energy in range
  if (sqrtS() < 0.36 * GeV || sqrtS() > 1.72 * GeV)
    throw Error("Invalid CMS energy for PLUTO_1984_I1260740");
  book(_cPi, "/TMP/nPi");
}


/// Perform the per-event analysis
void analyze(const Event& event) {
  Particles part = apply<FinalState>(event, "FS").particles();
  if (part.size() != 2) vetoEvent;
  double cTheta(0.);
  bool foundP(false), foundM(false);
  for (const Particle& p : part) {
    if (p.pid() == PID::PIPLUS) {
      foundP = true;
      cTheta = abs(p.momentum().z() / p.momentum().p3().mod());
    }
    else if (p.pid() == PID::PIMINUS)
      foundM = true;
  }
  if (!foundP || !foundM) vetoEvent;
  if (cTheta <= 0.2) _cPi->fill();
}


/// Normalise histograms etc., after the run
void finalize() {
  double fact = crossSection() / nanobarn / sumOfWeights();
  double sigma = _cPi->val() * fact / 0.2;
  double error = _cPi->err() * fact / 0.2;
  Estimate1DPtr mult;
  book(mult, 1, 1, 1);
  for (auto& b : mult->bins()) {
    if (inRange(sqrtS(), b.xMin(), b.xMax())) {
      b.set(sigma, error);
    }
  }
}

///@}


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

};

RIVET_DECLARE_PLUGIN(PLUTO_1984_I204487);

} ```