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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
  1// -*- C++ -*-
  2#include "Rivet/Analysis.hh"
  3#include "Rivet/Projections/Beam.hh"
  4#include "Rivet/Projections/FinalState.hh"
  5#include "Rivet/Projections/UnstableParticles.hh"
  6
  7namespace Rivet {
  8
  9
 10  /// @brief K+- Lambda asymmetries
 11  class DELPHI_1995_I382285 : public Analysis {
 12  public:
 13
 14    /// Constructor
 15    RIVET_DEFAULT_ANALYSIS_CTOR(DELPHI_1995_I382285);
 16
 17
 18    /// @name Analysis methods
 19    /// @{
 20
 21    /// Book histograms and initialise projections before the run
 22    void init() {
 23
 24      // Initialise and register projections
 25      declare(Beam(), "Beams");
 26      declare(FinalState(), "FS");
 27      declare(UnstableParticles(), "UFS");
 28
 29      // Book histograms
 30      book(_h_Kp, "/TMP/cos_Kp",20,-1.,1.);
 31      book(_h_Km, "/TMP/cos_Km",20,-1.,1.);
 32      book(_h_lm, "/TMP/cos_lm",20,-1.,1.);
 33      book(_h_lb, "/TMP/cos_lb",20,-1.,1.);
 34
 35    }
 36
 37
 38    /// Perform the per-event analysis
 39    void analyze(const Event& event) {
 40
 41      // Get beams and average beam momentum
 42      const ParticlePair& beams = apply<Beam>(event, "Beams").beams();
 43      const double meanBeamMom = ( beams.first.p3().mod() +
 44                                   beams.second.p3().mod() ) / 2.0;
 45      Vector3 beamAxis;
 46      if (beams.first.pid()==11) {
 47        beamAxis = beams.first .momentum().p3().unit();
 48      }
 49      else {
 50        beamAxis = beams.second.momentum().p3().unit();
 51      }
 52      MSG_DEBUG("Avg beam momentum = " << meanBeamMom);
 53      const UnstableParticles& ufs = apply<UnstableParticles>(event, "UFS");
 54      for (const Particle & p : ufs.particles(Cuts::abspid==3122 || Cuts::abspid==321 )) {
 55        double modp = p.momentum().p3().mod();
 56        if (p.abspid()==321) {
 57          if (modp<10. || modp>18.) continue;
 58          const double cK = beamAxis.dot(p.momentum().p3().unit());
 59          if (p.pid()>0)  _h_Kp->fill(cK);
 60          else            _h_Km->fill(cK);
 61        }
 62        else {
 63          if (modp<11.41 || modp>22.82) continue;
 64          const double cLam = beamAxis.dot(p.momentum().p3().unit());
 65          if (p.pid()>0)  _h_lm->fill(cLam);
 66          else            _h_lb->fill(cLam);
 67        }
 68      }
 69    }
 70
 71    pair<double,double> calcAsymmetry(const Estimate1DPtr& hist) {
 72      double sum1(0.), sum2(0.);
 73      for (const auto& bin : hist->bins()) {
 74        double Oi = bin.val();
 75        if (Oi==0.) continue;
 76        const double bi = 4.*(bin.xMax()+bin.xMin())/(3.+sqr(bin.xMax())+bin.xMax()*bin.xMin()+sqr(bin.xMin()));
 77        const double Ei = bin.errAvg();
 78        sum1 += sqr(bi/Ei);
 79        sum2 += bi/sqr(Ei)*Oi;
 80      }
 81      return make_pair(sum2/sum1,sqrt(1./sum1));
 82    }
 83
 84    /// Normalise histograms etc., after the run
 85    void finalize() {
 86       	normalize(_h_Kp);
 87       	normalize(_h_Km);
 88       	Estimate1DPtr sK;
 89        book(sK,"a_K");
 90       	asymm(_h_Kp,_h_Km,sK);
 91        pair<double,double> alpha = calcAsymmetry(sK);
 92        BinnedEstimatePtr<string> h_K;
 93        book(h_K, 1,1,1);
 94       	h_K->bin(1).set(-alpha.first, alpha.second);
 95
 96       	normalize(_h_lm);
 97       	normalize(_h_lb);
 98       	Estimate1DPtr sLam;
 99        book(sLam,"a_Lam");
100       	asymm(_h_lm,_h_lb,sLam);
101        alpha = calcAsymmetry(sLam);
102        BinnedEstimatePtr<string> h_lam;
103        book(h_lam, 1, 1, 2);
104       	h_lam->bin(1).set(alpha.first, alpha.second);
105    }
106
107    /// @}
108
109
110    /// @name Histograms
111    /// @{
112    Histo1DPtr  _h_Kp,_h_Km,_h_lm,_h_lb;
113    const string Ecm = "91.2";
114    /// @}
115
116
117  };
118
119
120  RIVET_DECLARE_PLUGIN(DELPHI_1995_I382285);
121
122
123}