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Rivet analyses reference

DELPHI_1995_I382285

Forward-Backward Asymmetry for $K^\pm$ and $\Lambda^0$,$\bar\Lambda^0$ at LEP1
Experiment: DELPHI (LEP)
Inspire ID: 382285
Status: VALIDATED
Authors:
  • Peter Richardson
References:
  • Z.Phys. C67 (1995) 1-14, 1995
Beams: e+ e-
Beam energies: ANY
Run details:
  • e+e-> hadrons

Forward-Backward Asymmetry for $K^\pm$ and $\Lambda^0$,$\bar\Lambda^0$ at LEP1, the paper goes on to extract the strange quark asymmetry but this involves a lot of corrections and therefore only the $K^\pm$ and $\Lambda^0$,$\bar\Lambda^0$ are included

Source code: DELPHI_1995_I382285.cc
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// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/Beam.hh"
#include "Rivet/Projections/FinalState.hh"
#include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {


  /// @brief K+- Lambda asymmetries
  class DELPHI_1995_I382285 : public Analysis {
  public:

    /// Constructor
    DEFAULT_RIVET_ANALYSIS_CTOR(DELPHI_1995_I382285);


    /// @name Analysis methods
    //@{

    /// Book histograms and initialise projections before the run
    void init() {

      // Initialise and register projections
      declare(Beam(), "Beams");
      declare(FinalState(), "FS");
      declare(UnstableParticles(), "UFS");

      // Book histograms
      book(_h_Kp, "/TMP/cos_Kp",20,-1.,1.);
      book(_h_Km, "/TMP/cos_Km",20,-1.,1.);
      book(_h_lm, "/TMP/cos_lm",20,-1.,1.);
      book(_h_lb, "/TMP/cos_lb",20,-1.,1.);

    }


    /// Perform the per-event analysis
    void analyze(const Event& event) {

      // Get beams and average beam momentum
      const ParticlePair& beams = apply<Beam>(event, "Beams").beams();
      const double meanBeamMom = ( beams.first.p3().mod() +
                                   beams.second.p3().mod() ) / 2.0;
      Vector3 beamAxis;
      if(beams.first.pid()==11) {
	beamAxis = beams.first .momentum().p3().unit();
      }
      else {
	beamAxis = beams.second.momentum().p3().unit();
      }
      MSG_DEBUG("Avg beam momentum = " << meanBeamMom);
      const UnstableParticles& ufs = apply<UnstableFinalState>(event, "UFS");
      for(const Particle & p : ufs.particles(Cuts::abspid==3122 || Cuts::abspid==321 )) {
	double modp = p.momentum().p3().mod();
	if(p.abspid()==321) {
	  if(modp<10. || modp>18.) continue;
	  double cK = beamAxis.dot(p.momentum().p3().unit());
	  if(p.pid()>0)
	    _h_Kp->fill(cK);
	  else
	    _h_Km->fill(cK);
	}
	else {
	  if(modp<11.41 || modp>22.82) continue;
	  double cLam = beamAxis.dot(p.momentum().p3().unit());
	  if(p.pid()>0)
	    _h_lm->fill(cLam);
	  else
	    _h_lb->fill(cLam);
	}
      }
    }
    
    pair<double,double> calcAsymmetry(Scatter2DPtr hist) {
      double sum1(0.),sum2(0.);
      for (auto bin : hist->points() ) {
	double Oi = bin.y();
	if(Oi==0.) continue;
	double bi = 4.*(bin.xMax()+bin.xMin())/(3.+sqr(bin.xMax())+bin.xMax()*bin.xMin()+sqr(bin.xMin()));
	double Ei = bin.yErrAvg();
	sum1 += sqr(bi/Ei);
	sum2 += bi/sqr(Ei)*Oi;
      }
      return make_pair(sum2/sum1,sqrt(1./sum1));
    }
    
    /// Normalise histograms etc., after the run
    void finalize() {
       	normalize(_h_Kp);
       	normalize(_h_Km);
       	Scatter2DPtr sK;
	book(sK,"a_K");
       	asymm(_h_Kp,_h_Km,sK);
	pair<double,double> alpha = calcAsymmetry(sK);
	Scatter2DPtr h_K;
	book(h_K, 1,1,1);
       	h_K->addPoint(91.2, -alpha.first, make_pair(0.5,0.5),
		      make_pair(alpha.second,alpha.second) );
	
       	normalize(_h_lm);
       	normalize(_h_lb);
       	Scatter2DPtr sLam;
	book(sLam,"a_Lam");
       	asymm(_h_lm,_h_lb,sLam);
	alpha = calcAsymmetry(sLam);
	Scatter2DPtr h_lam;
	book(h_lam, 1,1,2);
       	h_lam->addPoint(91.2, alpha.first, make_pair(0.5,0.5),
			make_pair(alpha.second,alpha.second) );
    }

    //@}


    /// @name Histograms
    //@{
    Histo1DPtr  _h_Kp,_h_Km,_h_lm,_h_lb;
    //@}


  };


  // The hook for the plugin system
  DECLARE_RIVET_PLUGIN(DELPHI_1995_I382285);


}