Rivet analyses

title: 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: (45.6, 45.6)GeV

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

```c++ // -- 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
RIVET_DEFAULT_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<UnstableParticles>(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;
      const 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;
      const 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(const Estimate1DPtr& hist) {
  double sum1(0.), sum2(0.);
  for (const auto& bin : hist->bins()) {
    double Oi = bin.val();
    if (Oi == 0.) continue;
    const double bi = 4. * (bin.xMax() + bin.xMin())
        / (3. + sqr(bin.xMax()) + bin.xMax() * bin.xMin() + sqr(bin.xMin()));
    const double Ei = bin.errAvg();
    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);
  Estimate1DPtr sK;
  book(sK, "a_K", 20, -1., 1.);
  asymm(_h_Kp, _h_Km, sK);
  pair<double, double> alpha = calcAsymmetry(sK);
  BinnedEstimatePtr<string> h_K;
  book(h_K, 1, 1, 1);
  h_K->bin(1).set(-alpha.first, alpha.second);

  normalize(_h_lm);
  normalize(_h_lb);
  Estimate1DPtr sLam;
  book(sLam, "a_Lam", 20, -1., 1.);
  asymm(_h_lm, _h_lb, sLam);
  alpha = calcAsymmetry(sLam);
  BinnedEstimatePtr<string> h_lam;
  book(h_lam, 1, 1, 2);
  h_lam->bin(1).set(alpha.first, alpha.second);
}

/// @}


/// @name Histograms
/// @{
Histo1DPtr _h_Kp, _h_Km, _h_lm, _h_lb;
const string Ecm = "91.2";
/// @}

};

RIVET_DECLARE_PLUGIN(DELPHI_1995_I382285);

} ```