Rivet analyses

γγ → π⁺π⁻ ($2<\sqrt{s}<6$ GeV) and K⁺K⁻ ($2.25<\sqrt{s}<4$ GeV)

Experiment: ALEPH (LEP)

Inspire ID: 626022

Status: VALIDATED

Authors: none listed

References: - Phys.Lett.B 569 (2003) 140-150

Beams: 22 22

Beam energies: ANY

Run details: - gamma gamma to hadrons

Measurement of the differential cross section for γγ → π⁺π⁻ ($2<\sqrt{s}<6$ GeV) and K⁺K⁻ ($2.25<\sqrt{s}<4$ GeV). The cross section as a function of the centre-of-mass energy of the photonic collision is measured, and the differential cross section with respect to the meson scattering angle are measured.

Source code:`ALEPH_2003_I626022.cc`

// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/FastJets.hh"
#include "Rivet/Projections/FinalState.hh"
#include "Rivet/Projections/LeptonFinder.hh"
#include "Rivet/Projections/MissingMomentum.hh"
#include "Rivet/Projections/PromptFinalState.hh"

namespace Rivet {


  /// @brief gamma gamma -> pi+pi-/K+ K-
  class ALEPH_2003_I626022 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(ALEPH_2003_I626022);


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

    /// Book histograms and initialise projections before the run
    void init() {
      // check CMS energy in range
      if (sqrtS() < 2. * GeV || sqrtS() > 6. * GeV) throw Error("Invalid CMS energy for ");
      // Final state
      declare(FinalState(), "FS");
      // histos
      book(_h_Pi, 1, 1, 1);
      if (sqrtS() < 4.) book(_h_K, 2, 1, 1);
      book(_cPi, "/TMP/nPi_");
      book(_cK, "/TMP/nK_");
    }


    /// Perform the per-event analysis
    void analyze(const Event& event) {
      Particles part = apply<FinalState>(event, "FS").particles();
      if (part.size() != 2) vetoEvent;
      if (part[0].pid() != -part[1].pid()) vetoEvent;
      double cTheta(0.);
      bool foundPi(false), foundK(false);
      for (const Particle& p : part) {
        if (p.pid() == PID::PIPLUS) {
          foundPi = true;
          cTheta = abs(p.momentum().z() / p.momentum().p3().mod());
        }
        else if (p.pid() == PID::KPLUS) {
          foundK = true;
          cTheta = abs(p.momentum().z() / p.momentum().p3().mod());
        }
      }
      if (!foundPi && !foundK) vetoEvent;
      if (foundPi && _h_Pi) _h_Pi->fill(cTheta);
      if (foundK && _h_K) _h_K->fill(cTheta);
      if (foundPi)
        _cPi->fill();
      else if (foundK)
        _cK->fill();
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      double fact = crossSection() / nanobarn / sumOfWeights();
      if (_h_Pi) scale(_h_Pi, fact);
      if (_h_K) scale(_h_K, fact);
      for (unsigned int ih = 3; ih < 5; ++ih) {
        CounterPtr count = ih == 3 ? _cPi : _cK;
        double sigma = count->val() * fact;
        double error = count->err() * fact;
        // hist for axis
        Estimate1DPtr cross;
        book(cross, ih, 1, 1);
        for (auto& b : cross->bins()) {
          if (inRange(sqrtS(), b.xMin(), b.xMax())) {
            b.set(sigma, error);
          }
        }
      }
    }

    ///@}


    /// @name Histograms
    ///@{
    Histo1DPtr _h_Pi, _h_K;
    CounterPtr _cPi, _cK;
    ///@}
  };


  RIVET_DECLARE_PLUGIN(ALEPH_2003_I626022);

}

Rivet analyses

γγ → π+π− ($2<\sqrt{s}<6$ GeV) and K+K− ($2.25<\sqrt{s}<4$ GeV)

Source code:ALEPH_2003_I626022.cc

γγ → π⁺π⁻ ($2<\sqrt{s}<6$ GeV) and K⁺K⁻ ($2.25<\sqrt{s}<4$ GeV)

Source code:`ALEPH_2003_I626022.cc`