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DM2_1990_I297706

Cross section for $e^+e^-\to p\bar{p}$ and $\Lambda\bar{\Lambda}$ at 2.4 GeV
Experiment: DM2 (DCI)
Inspire ID: 297706
Status: VALIDATED
Authors:
  • Peter Richardson
References:
  • Z.Phys. C48 (1990) 23-28, 1990
Beams: e+ e-
Beam energies: ANY
Run details:
  • e+e- to hadrons

Measurement of the cross section for $e^+e^-\to p\bar{p}$ and $\Lambda\bar{\Lambda}$ at 2.4 GeV.

Source code: DM2_1990_I297706.cc
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// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/FinalState.hh"
#include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {


  /// @brief Add a short analysis description here
  class DM2_1990_I297706 : public Analysis {
  public:

    /// Constructor
    DEFAULT_RIVET_ANALYSIS_CTOR(DM2_1990_I297706);


    /// @name Analysis methods
    //@{

    /// Book histograms and initialise projections before the run
    void init() {
      // Initialise and register projections
      declare(FinalState(), "FS");
      declare(UnstableParticles(), "UFS");
      book(_nProton,  "/TMP/nProton" );
      book(_nLambda,  "/TMP/nLambda" );
    }

    void findChildren(const Particle & p,map<long,int> & nRes, int &ncount) {
      for (const Particle &child : p.children()) {
	if(child.children().empty()) {
	  nRes[child.pid()]-=1;
	  --ncount;
	}
	else
	  findChildren(child,nRes,ncount);
      }
    }

    /// Perform the per-event analysis
    void analyze(const Event& event) {
      const FinalState& fs = apply<FinalState>(event, "FS");
      // total hadronic and muonic cross sections
      map<long,int> nCount;
      int ntotal(0);
      for (const Particle& p : fs.particles()) {
	nCount[p.pid()] += 1;
	++ntotal;
      }
      if(ntotal==2 && nCount[2212]==1 && nCount[-2212]==1)
	_nProton->fill();
      
      // find the Lambdas
      const FinalState& ufs = apply<UnstableParticles>(event, "UFS");
      for(unsigned int ix=0;ix<ufs.particles().size();++ix) {
	const Particle& p1 = ufs.particles()[ix];
	if(abs(p1.pid())!=3122) continue;
	bool matched = false;
	// check fs
	bool fs = true;
	for (const Particle & child : p1.children()) {
	  if(child.pid()==p1.pid()) {
	    fs = false;
	    break;
	  }
	}
	if(!fs) continue;
	// find the children
	map<long,int> nRes = nCount;
	int ncount = ntotal;
	findChildren(p1,nRes,ncount);
	for(unsigned int iy=ix+1;iy<ufs.particles().size();++iy) {
	  const Particle& p2 = ufs.particles()[iy];
	  if(abs(p2.pid())!=3122) continue;
	  // check fs
	  bool fs = true;
	  for (const Particle & child : p2.children()) {
	    if(child.pid()==p2.pid()) {
	      fs = false;
	      break;
	    }
	  }
	  if(!fs) continue;
	  map<long,int> nRes2 = nRes;
	  int ncount2 = ncount;
	  findChildren(p2,nRes2,ncount2);
	  if(ncount2!=0) continue;
	  matched=true;
	  for(auto const & val : nRes2) {
	    if(val.second!=0) {
	      matched = false;
	      break;
	    }
	  }
	  if(matched) {
	    _nLambda->fill();
	    break;
	  }
	}
	if(matched) break;
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      double fact = crossSection()/ sumOfWeights() /picobarn;
      for(unsigned int ix=1;ix<3;++ix) {
	double sigma,error;
	if(ix==1) {
	  sigma = _nProton->val()*fact;
	  error = _nProton->err()*fact;
	}
	else {
	  sigma = _nLambda->val()*fact;
	  error = _nLambda->err()*fact;
	}
	Scatter2D temphisto(refData(ix, 1, 1));
	Scatter2DPtr mult;
	book(mult, ix, 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()/GeV, x-ex2.first, x+ex2.second)) {
	    mult->addPoint(x, sigma, ex, make_pair(error,error));
	  }
	  else {
	    mult->addPoint(x, 0., ex, make_pair(0.,.0));
	  }
	}
      }
    }
    //@}

    /// @name Histograms
    //@{
    CounterPtr _nProton,_nLambda;
    //@}

  };


  // The hook for the plugin system
  DECLARE_RIVET_PLUGIN(DM2_1990_I297706);


}