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DELPHI_1999_I448370

Charged particle fragmentation functions at LEP1
Experiment: DELPHI (LEP)
Inspire ID: 448370
Status: VALIDATED
Authors:
  • Peter Richardson
References:
  • Eur.Phys.J. C6 (1999) 19-33
Beams: e+ e-
Beam energies: ANY
Run details:
  • e+e-> hadrons

The transverse, longitudinal and asymmetric components of the fragmentation function are measured from the inclusive charged particles produced in $e^+e^-$ collisions at LEP, include separation of bottom and light quark(uds) events.

Source code: DELPHI_1999_I448370.cc
  1// -*- C++ -*-
  2#include "Rivet/Analysis.hh"
  3#include "Rivet/Projections/Beam.hh"
  4#include "Rivet/Projections/ChargedFinalState.hh"
  5
  6#define I_KNOW_THE_INITIAL_QUARKS_PROJECTION_IS_DODGY_BUT_NEED_TO_USE_IT
  7#include "Rivet/Projections/InitialQuarks.hh"
  8
  9namespace Rivet {
 10
 11
 12  /// @brief Add a short analysis description here
 13  class DELPHI_1999_I448370 : public Analysis {
 14  public:
 15
 16    /// Constructor
 17    RIVET_DEFAULT_ANALYSIS_CTOR(DELPHI_1999_I448370);
 18
 19
 20    /// @name Analysis methods
 21    //@{
 22
 23    /// Book histograms and initialise projections before the run
 24    void init() {
 25      declare(Beam(), "Beams");
 26      declare(ChargedFinalState(), "FS");
 27      declare(InitialQuarks(), "IQF");
 28      
 29      // Book histograms
 30       book(_h_F_T       , 1, 1, 1);
 31       book(_h_F_L       , 2, 1, 1);
 32       book(_h_F_A       , 3, 1, 1);
 33       book(_h_F_TL      , 4, 1, 1);
 34       book(_h_F_T_total , 5, 1, 1);
 35       book(_h_F_L_total , 5, 1, 2);
 36       book(_h_F_TL_total, 5, 1, 3);
 37       book(_h_b_F_T     , 7, 1, 1);
 38       book(_h_b_F_L     , 7, 1, 2);
 39       book(_h_light_F_T , 8, 1, 1);
 40       book(_h_light_F_L , 8, 1, 2);
 41       book(_n_bottom    , 9, 1, 1);
 42       book(_n_light     , 9, 1, 2);
 43      
 44       book(_c_light , "/TMP/wLight");
 45       book(_c_bottom, "/TMP/wBottom");
 46       book(_c_total , "/TMP/wTotal");
 47
 48    }
 49
 50
 51    /// Perform the per-event analysis
 52    void analyze(const Event& event) {
 53      // First, veto on leptonic events by requiring at least 4 charged FS particles
 54      const FinalState& fs = apply<FinalState>(event, "FS");
 55      const size_t numParticles = fs.particles().size();
 56
 57      // Even if we only generate hadronic events, we still need a cut on numCharged >= 2.
 58      if (numParticles < 2) {
 59        MSG_DEBUG("Failed leptonic event cut");
 60        vetoEvent;
 61      }
 62      MSG_DEBUG("Passed leptonic event cut");
 63
 64      int flavour = 0;
 65      const InitialQuarks& iqf = apply<InitialQuarks>(event, "IQF");
 66
 67      // If we only have two quarks (qqbar), just take the flavour.
 68      // If we have more than two quarks, look for the highest energetic q-qbar pair.
 69      if (iqf.particles().size() == 2) {
 70        flavour = iqf.particles().front().abspid();
 71      }
 72      else {
 73        map<int, double> quarkmap;
 74        for (const Particle& p : iqf.particles()) {
 75          if (quarkmap[p.pid()] < p.E()) {
 76            quarkmap[p.pid()] = p.E();
 77          }
 78        }
 79        double maxenergy = 0.;
 80        for (int i = 1; i <= 5; ++i) {
 81          if (quarkmap[i]+quarkmap[-i] > maxenergy) {
 82            flavour = i;
 83          }
 84        }
 85      }
 86      if     (flavour==5) _c_bottom->fill();
 87      else if(flavour!=4) _c_light ->fill();
 88      _c_total->fill();
 89      // Get beams and average beam momentum
 90      const ParticlePair& beams = apply<Beam>(event, "Beams").beams();
 91      const double meanBeamMom = ( beams.first.p3().mod() +
 92                                   beams.second.p3().mod() ) / 2.0;
 93      MSG_DEBUG("Avg beam momentum = " << meanBeamMom);
 94      Vector3 axis;
 95      if(beams.first.pid()>0)
 96	axis = beams.first .momentum().p3().unit();
 97      else
 98	axis = beams.second.momentum().p3().unit();
 99
100      // loop over charged particles
101      double v=0.8, v2=sqr(v), v5=v2*v2*v;
102      for (const Particle& p : fs.particles()) {
103        double xp = p.p3().mod()/meanBeamMom;
104	double ctheta = axis.dot(p.momentum().p3().unit());
105	if(abs(ctheta)<0.8) {
106	  double WT = 0.5 /v5*(5.*sqr(ctheta)*(3.-v2)-v2*(5.-3.*v2));
107	  double WL = 0.25/v5*(v2*(5.+3.*v2)-5.*sqr(ctheta)*(3.+v2));
108	  double WA = 2.*ctheta/v2/v;
109	  _h_F_T  ->fill(xp,WT);
110	  _h_F_L  ->fill(xp,WL);
111	  _h_F_TL ->fill(xp,(WL+WT));
112	  _h_F_T_total ->fill(xp,0.5*xp*WT);
113	  _h_F_L_total ->fill(xp,0.5*xp*WL);
114	  _h_F_TL_total->fill(xp,0.5*xp*(WL+WT));
115	  if(p.charge()>0) {
116	    _h_F_A->fill(xp, WA);
117	  }
118	  else {
119	    _h_F_A->fill(xp,-WA);
120	  }
121	  if(flavour==5) {
122	    _h_b_F_T  ->fill(xp,WT);
123	    _h_b_F_L  ->fill(xp,WL);
124	  }
125	  else if(flavour!=4) {
126	    _h_light_F_T->fill(xp,WT);
127	    _h_light_F_L->fill(xp,WL);
128	  }
129	}
130      }
131
132      if(flavour==5)
133	_n_bottom->fill(91.2,fs.particles().size());
134      else if(flavour!=4)
135	_n_light->fill(91.2,fs.particles().size());
136
137    }
138
139
140    /// Normalise histograms etc., after the run
141    void finalize() {
142      scale(_h_F_T ,1./ *_c_total);
143      scale(_h_F_L ,1./ *_c_total);
144      scale(_h_F_A ,1./ *_c_total);
145      scale(_h_F_TL,1./ *_c_total);
146      {Scatter2DPtr temp; divide(_h_F_L, _h_F_T , book(temp, 6, 1, 1));}
147      {Scatter2DPtr temp; divide(_h_F_L, _h_F_TL, book(temp, 6, 1, 2));}
148      scale(_h_F_T_total ,1./ *_c_total);
149      scale(_h_F_L_total ,1./ *_c_total);
150      scale(_h_F_TL_total,1./ *_c_total);
151      scale(_h_b_F_T ,1./ *_c_bottom);
152      scale(_h_b_F_L ,1./ *_c_bottom);
153      scale(_h_light_F_T ,1./ *_c_light);
154      scale(_h_light_F_L ,1./ *_c_light);
155      scale(_n_bottom ,1./ *_c_bottom);
156      scale(_n_light ,1./ *_c_light);
157    }
158
159    //@}
160
161
162    /// @name Histograms
163    //@{
164    Histo1DPtr _h_F_T,_h_F_L,_h_F_A,_h_F_TL,_h_b_F_T,_h_b_F_L,_h_light_F_T,_h_light_F_L,_n_light,_n_bottom;
165    Histo1DPtr _h_F_T_total,_h_F_L_total,_h_F_TL_total;
166    CounterPtr _c_light,_c_bottom,_c_total;
167    //@}
168
169
170  };
171
172
173  // The hook for the plugin system
174  RIVET_DECLARE_PLUGIN(DELPHI_1999_I448370);
175
176
177}