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ALEPH_1995_I398426

Production of $B^*$ mesons at LEP1
Experiment: ALEPH (LEP)
Inspire ID: 398426
Status: VALIDATED NOHEPDATA
Authors:
  • Peter Richardson
References:
  • Z.Phys. C69 (1996) 393-404
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: ALEPH_1995_I398426.cc
  1// -*- C++ -*-
  2#include "Rivet/Analysis.hh"
  3#include "Rivet/Projections/ChargedFinalState.hh"
  4#include "Rivet/Projections/UnstableParticles.hh"
  5
  6namespace Rivet {
  7
  8
  9  /// @brief Add a short analysis description here
 10  class ALEPH_1995_I398426 : public Analysis {
 11  public:
 12
 13    /// Constructor
 14    RIVET_DEFAULT_ANALYSIS_CTOR(ALEPH_1995_I398426);
 15
 16
 17    /// @name Analysis methods
 18    //@{
 19
 20    /// Book histograms and initialise projections before the run
 21    void init() {
 22
 23      // // Initialise and register projections
 24      declare(ChargedFinalState(), "FS");
 25      declare(UnstableParticles(), "UFS");
 26
 27      // Book histograms
 28      book(_h_ctheta1, 3,1,1);
 29      book(_h_ctheta2, "/TMP/ctheta",20,-1.,1.);
 30      book(_c_hadron , "/TMP/chadron");
 31      book(_c_bStar  , "/TMP/cbStar ");
 32      book(_c_B      , "/TMP/cB     ");
 33    }
 34
 35
 36    /// Perform the per-event analysis
 37    void analyze(const Event& event) {
 38      // First, veto on leptonic events by requiring at least 4 charged FS particles
 39      const FinalState& fs = apply<FinalState>(event, "FS");
 40      const size_t numParticles = fs.particles().size();
 41
 42      // Even if we only generate hadronic events, we still need a cut on numCharged >= 2.
 43      if (numParticles < 2) {
 44        MSG_DEBUG("Failed leptonic event cut");
 45        vetoEvent;
 46      }
 47      MSG_DEBUG("Passed leptonic event cut");
 48
 49      _c_hadron->fill();
 50      // loop over the particles
 51      for(const Particle& p : apply<UnstableParticles>(event, "UFS").particles(Cuts::abspid==513 or Cuts::abspid==523 or
 52									       Cuts::abspid==511 or Cuts::abspid==521)) {
 53	int sign = p.pid()/p.abspid();
 54	// count number of Bs not from mixing or B*
 55	if(p.abspid()==511 || p.abspid()==521) {
 56	  if(p.parents()[0].abspid()==p.abspid()) continue;
 57	  if(p.parents()[0].abspid()==513 || p.parents()[0].abspid()==523) continue;
 58	  _c_B->fill(); 
 59	}
 60	// B*
 61	else {
 62	  _c_bStar->fill();
 63	  Particle decay;
 64	  if(p.children().size()!=2) continue;
 65	  int mid = p.abspid()-2;
 66	  if(p.children()[0].pid()==sign*mid && 
 67	     p.children()[1].pid()==22) {
 68	    decay = p.children()[1];
 69	  }
 70	  else if(p.children()[1].pid()==sign*mid && 
 71		  p.children()[0].pid()==22) {
 72	    decay = p.children()[0];
 73	  }
 74	  else
 75	    continue;
 76	  LorentzTransform boost = LorentzTransform::mkFrameTransformFromBeta(p.momentum().betaVec());
 77	  Vector3 e1z = p.p3().unit();	
 78	  FourMomentum pp = boost.transform(decay.momentum());
 79	  Vector3 axis1 = boost.transform(decay.momentum()).p3().unit();
 80	  double ctheta = e1z.dot(axis1);
 81	  _h_ctheta1->fill(ctheta);
 82	  _h_ctheta2->fill(ctheta);
 83	}
 84      }
 85    }
 86    
 87    pair<double,double> calcRho(Histo1DPtr hist) {
 88      if(hist->numEntries()==0.) return make_pair(0.,0.);
 89      double sum1(0.),sum2(0.);
 90      for (auto bin : hist->bins() ) {
 91	double Oi = bin.area();
 92	if(Oi==0.) continue;
 93	double ai = 0.125*( -bin.xMin()*(3.+sqr(bin.xMin())) + bin.xMax()*(3.+sqr(bin.xMax())));
 94	double bi = 0.375*( -bin.xMin()*(1.-sqr(bin.xMin())) + bin.xMax()*(1.-sqr(bin.xMax())));
 95	double Ei = bin.areaErr();
 96	sum1 += sqr(bi/Ei);
 97	sum2 += bi/sqr(Ei)*(Oi-ai);
 98      }
 99      return make_pair(sum2/sum1,sqrt(1./sum1));
100    }
101
102    /// Normalise histograms etc., after the run
103    void finalize() {
104      // polarization
105      scale(_h_ctheta1,1./_c_hadron->val());
106      normalize(_h_ctheta2);
107      pair<double,double> rho = calcRho(_h_ctheta2);
108      Scatter2DPtr h_rho;
109      book(h_rho,2,1,1);
110      h_rho->addPoint(0.5, rho.first, make_pair(0.5,0.5),
111		      make_pair(rho.second,rho.second) );
112      Scatter2DPtr h1;
113      book(h1,1,1,1);
114      Counter ctemp = *_c_bStar+*_c_B;
115      // no of B*/B+B*
116      double val = _c_bStar->val()/ctemp.val();
117      double err = val*sqrt(sqr(_c_bStar->err()/_c_bStar->val())+sqr(ctemp.err()/ctemp.val()));
118      h1->addPoint(0.5,val,make_pair(0.5,0.5),make_pair(err,err) );
119    }
120
121    //@}
122
123
124    /// @name Histograms
125    //@{
126    Histo1DPtr _h_ctheta1, _h_ctheta2;
127    CounterPtr _c_hadron,_c_bStar,_c_B;
128    //@}
129
130
131  };
132
133
134  // The hook for the plugin system
135  RIVET_DECLARE_PLUGIN(ALEPH_1995_I398426);
136
137
138}