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/FinalState.hh"
#include "Rivet/Projections/FastJets.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`