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OPAL_1996_I428493

Production of $B^*$ mesons at LEP1
Experiment: OPAL (LEP)
Inspire ID: 428493
Status: VALIDATED
Authors:
  • Peter Richardson
References:
  • Production of $B^*$ mesons at LEP1
Beams: e- e+
Beam energies: ANY
Run details:
  • e+e- to hadrons

The polarization and ratio of vector to pseudoscalar for $B$ meson production at LEP1.

Source code: OPAL_1996_I428493.cc
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// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/ChargedFinalState.hh"
#include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {


  /// @brief Add a short analysis description here
  class OPAL_1996_I428493 : public Analysis {
  public:

    /// Constructor
    DEFAULT_RIVET_ANALYSIS_CTOR(OPAL_1996_I428493);


    /// @name Analysis methods
    //@{

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

      // // Initialise and register projections
      declare(ChargedFinalState(), "FS");
      declare(UnstableParticles(), "UFS");

      // Book histograms
      book(_h_ctheta1, 3,1,1);
      book(_h_ctheta2, "/TMP/ctheta",20,-1.,1.);
      book(_c_hadron , "/TMP/chadron");
      book(_c_bStar  , "/TMP/cbStar ");
      book(_c_B      , "/TMP/cB     ");
    }


    /// Perform the per-event analysis
    void analyze(const Event& event) {
      // First, veto on leptonic events by requiring at least 4 charged FS particles
      const FinalState& fs = apply<FinalState>(event, "FS");
      const size_t numParticles = fs.particles().size();

      // Even if we only generate hadronic events, we still need a cut on numCharged >= 2.
      if (numParticles < 2) {
        MSG_DEBUG("Failed leptonic event cut");
        vetoEvent;
      }
      MSG_DEBUG("Passed leptonic event cut");

      _c_hadron->fill();
      // loop over the particles
      for(const Particle& p : apply<UnstableParticles>(event, "UFS").particles(Cuts::abspid==513 or Cuts::abspid==523 or
									       Cuts::abspid==511 or Cuts::abspid==521)) {
	int sign = p.pid()/p.abspid();
	// count number of Bs not from mixing or B*
	if(p.abspid()==511 || p.abspid()==521) {
	  if(p.parents()[0].abspid()==p.abspid()) continue;
	  if(p.parents()[0].abspid()==513 || p.parents()[0].abspid()==523) continue;
	  _c_B->fill(); 
	}
	// B*
	else {
	  _c_bStar->fill();
	  Particle decay;
	  if(p.children().size()!=2) continue;
	  int mid = p.abspid()-2;
	  if(p.children()[0].pid()==sign*mid && 
	     p.children()[1].pid()==22) {
	    decay = p.children()[1];
	  }
	  else if(p.children()[1].pid()==sign*mid && 
		  p.children()[0].pid()==22) {
	    decay = p.children()[0];
	  }
	  else
	    continue;
	  LorentzTransform boost = LorentzTransform::mkFrameTransformFromBeta(p.momentum().betaVec());
	  Vector3 e1z = p.p3().unit();	
	  FourMomentum pp = boost.transform(decay.momentum());
	  Vector3 axis1 = boost.transform(decay.momentum()).p3().unit();
	  double ctheta = e1z.dot(axis1);
	  _h_ctheta1->fill(ctheta);
	  _h_ctheta2->fill(ctheta);
	}
      }
    }
    
    pair<double,double> calcRho(Histo1DPtr hist) {
      if(hist->numEntries()==0.) return make_pair(0.,0.);
      double sum1(0.),sum2(0.);
      for (auto bin : hist->bins() ) {
	double Oi = bin.area();
	if(Oi==0.) continue;
	double ai = 0.125*( -bin.xMin()*(3.+sqr(bin.xMin())) + bin.xMax()*(3.+sqr(bin.xMax())));
	double bi = 0.375*( -bin.xMin()*(1.-sqr(bin.xMin())) + bin.xMax()*(1.-sqr(bin.xMax())));
	double Ei = bin.areaErr();
	sum1 += sqr(bi/Ei);
	sum2 += bi/sqr(Ei)*(Oi-ai);
      }
      return make_pair(sum2/sum1,sqrt(1./sum1));
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      // polarization
      scale(_h_ctheta1,1./_c_hadron->val());
      normalize(_h_ctheta2);
      pair<double,double> rho = calcRho(_h_ctheta2);
      Scatter2DPtr h_rho;
      book(h_rho,2,1,1);
      h_rho->addPoint(0.5, rho.first, make_pair(0.5,0.5),
		      make_pair(rho.second,rho.second) );
      Scatter2DPtr h1;
      book(h1, 1,1,1);
      Counter ctemp = *_c_bStar+*_c_B;
      // no of B*/B+B*
      double val = _c_bStar->val()/ctemp.val();
      double err = val*sqrt(sqr(_c_bStar->err()/_c_bStar->val())+sqr(ctemp.err()/ctemp.val()));
      h1->addPoint(0.5,val,make_pair(0.5,0.5),make_pair(err,err) );
    }

    //@}


    /// @name Histograms
    //@{
    Histo1DPtr _h_ctheta1, _h_ctheta2;
    CounterPtr _c_hadron,_c_bStar,_c_B;
    //@}


  };


  // The hook for the plugin system
  DECLARE_RIVET_PLUGIN(OPAL_1996_I428493);


}