Rivet analyses

γγ → π+π− 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 γγ → π+π−. 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++ -*-
#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);

}