Rivet analyses

γγ → π⁺π⁻ ($0.5<\sqrt{s}<3.25$ GeV) and K⁺K⁻ ($1.25<\sqrt{s}<3.5$ GeV)

Experiment: TPC (PEP)

Inspire ID: 228072

Status: VALIDATED

Authors: - Peter Richardson

References: - Phys.Rev.Lett. 57 (1986) 404, 1986

Beams: 22 22

Beam energies: ANY

Run details: - gamma gamma to hadrons

Measurement of the differential cross section for γγ → π⁺π⁻ ($0.5<\sqrt{s}<3.25$ GeV) and K⁺K⁻ ($1.25<\sqrt{s}<3.5$ GeV). The cross section as a function of the centre-of-mass energy of the photonic collision is measured

Source code:`TPC_1986_I228072.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 TPC_1986_I228072 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(TPC_1986_I228072);


    /// @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() < 0.5 * GeV || sqrtS() > 3.5 * GeV) throw Error("Invalid CMS energy for TPC_1986_I228072");

      // Book histograms
      book(_cPi[0], "/TMP/nPi_06");
      book(_cPi[1], "/TMP/nPi_03");
      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 (cTheta > 0.6) vetoEvent;
      if (foundPi) {
        _cPi[0]->fill();
        if (cTheta < 0.3) _cPi[1]->fill();
      }
      else if (foundK)
        _cK->fill();
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      double fact = crossSection() / nanobarn / sumOfWeights();
      for (unsigned int ih = 1; ih < 6; ++ih) {
        if (ih == 2 || ih == 3) continue;
        double sigma(0.), error(0.);
        CounterPtr count;
        if (ih == 1) {
          count = _cPi[0];
        }
        else if (ih == 4) {
          count = _cPi[1];
        }
        else if (ih == 5) {
          count = _cK;
        }
        else
          assert(false);
        if (count->numEntries() == 0) continue;
        sigma = count->val() * fact;
        error = count->err() * fact;
        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
    ///@{
    CounterPtr _cPi[2], _cK;
    ///@}
  };


  RIVET_DECLARE_PLUGIN(TPC_1986_I228072);

}

Rivet analyses

γγ → π+π− ($0.5<\sqrt{s}<3.25$ GeV) and K+K− ($1.25<\sqrt{s}<3.5$ GeV)

Source code:TPC_1986_I228072.cc

γγ → π⁺π⁻ ($0.5<\sqrt{s}<3.25$ GeV) and K⁺K⁻ ($1.25<\sqrt{s}<3.5$ GeV)

Source code:`TPC_1986_I228072.cc`