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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:
References:
- Z.Phys. C67 (1995) 1-14, 1995
Beams: e+ e-
Beam energies: ANY
Run details:
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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129 | // -*- 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;
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
RIVET_DECLARE_PLUGIN(DELPHI_1995_I382285);
}
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