Rivet Analyses Reference

MARKII_1984_I195739

$\gamma\gamma\to\pi^+\pi^-/K^+K^-$ for centre-of-mass energies between 1.6 and 2.5 GeV
Experiment: MARKII (PEP)
Inspire ID: 195739
Status: VALIDATED
Authors:
  • Peter Richardson
References:
  • Phys.Rev.D 30 (1984) 851, 1984
Beams: 22 22
Beam energies: ANY
Run details:
  • gamma gamma to hadrons

Measurement of the differential cross section for $\gamma\gamma\to\pi^+\pi^-/K^+K^-$ for $1.6 \text{GeV} < W < 2.5 \text{GeV}$.

Source code: MARKII_1984_I195739.cc
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// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/FinalState.hh"

namespace Rivet {


  /// @brief gamma gamma -> pi+pi-/K+ K-
  class MARKII_1984_I195739 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(MARKII_1984_I195739);


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

    /// Book histograms and initialise projections before the run
    void init() {
      declare(FinalState(),"FS");
      // check CMS energy in range
      if(sqrtS()<1.6*GeV || sqrtS()>2.5*GeV)
	throw Error("Invalid CMS energy for MARKII_1984_I195739");
      book(_cPiK, "/TMP/nPiK_");
    }


    /// Perform the per-event analysis
    void analyze(const Event& event) {
      Particles part = applyProjection<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>0.3) vetoEvent;
      _cPiK->fill();
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      double fact = crossSection()/nanobarn/sumOfWeights();
      double sigma = _cPiK->val()*fact;
      double error = _cPiK->err()*fact;
      Scatter2D temphisto(refData(1, 1, 1));
      Scatter2DPtr cross;
      book(cross, 1, 1, 1);
      for (size_t b = 0; b < temphisto.numPoints(); b++) {
	const double x  = temphisto.point(b).x();
	pair<double,double> ex = temphisto.point(b).xErrs();
	pair<double,double> ex2 = ex;
	if(ex2.first ==0.) ex2. first=0.0001;
	if(ex2.second==0.) ex2.second=0.0001;
	if (inRange(sqrtS(), x-ex2.first, x+ex2.second)) {
	  cross->addPoint(x, sigma, ex, make_pair(error,error));
	}
	else {
	  cross->addPoint(x, 0., ex, make_pair(0.,.0));
	}
      }
    }

    ///@}


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


  };


  RIVET_DECLARE_PLUGIN(MARKII_1984_I195739);

}