rivet is hosted by Hepforge, IPPP Durham

Rivet analyses reference

HRS_1987_I250823

$D^{*\pm}$ polarization at 29 GeV
Experiment: HRS (PEP)
Inspire ID: 250823
Status: VALIDATED
Authors:
  • Peter Richardson
References:
  • Phys.Lett. B199 (1987) 585-590
Beams: e- e+
Beam energies: ANY
Run details:
  • e+e- to hadrons

The polarization of $D^{*\pm}$ mesons produced in $e^+e^-$ collisions is measured for a centre-of-mass energy of 29 GeV.

Source code: HRS_1987_I250823.cc
  1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/Beam.hh"
#include "Rivet/Projections/FinalState.hh"
#include "Rivet/Projections/UnstableParticles.hh"
#include "Rivet/Projections/Sphericity.hh"

namespace Rivet {


  /// @brief D*+/- polarization at 29 GeV
  class HRS_1987_I250823 : public Analysis {
  public:

    /// Constructor
    DEFAULT_RIVET_ANALYSIS_CTOR(HRS_1987_I250823);


    /// @name Analysis methods
    //@{

    /// Book histograms and initialise projections before the run
    void init() {
      declare(Beam(), "Beams");
      declare(Sphericity(FinalState()), "Sphericity");
      declare(UnstableParticles(), "UFS" );
      for(unsigned int i=0;i<9;++i) {
       	unsigned int ix(0),iy(1);
       	if(i<3) {
       	  ix=1;
       	  iy=i+1;
       	}
       	else if(i==3) {
       	  ix=2;
       	}
       	else if(i<6) {
       	  ix=3;
       	  iy=i-3;
       	}
       	else {
       	  ix=i-2;
       	}
	book(_p_rho00[i],ix,iy,1);
	book(_p_rho11[i],ix,iy,2);
	book(_p_rho10[i],ix,iy,3);
      }
    }


    /// 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;
      MSG_DEBUG("Avg beam momentum = " << meanBeamMom);
      Vector3 axis;
      if(beams.first.pid()>0)
	axis = beams.first .momentum().p3().unit();
      else
	axis = beams.second.momentum().p3().unit();
      
      // sphericity, to define an axis
      const Sphericity& sphericity = apply<Sphericity>(event, "Sphericity");

      // loop over the particles
      for(const Particle& p : apply<UnstableParticles>(event, "UFS").particles(Cuts::abspid==413)) {
	int sign = p.pid()/p.abspid();
	Particle decay;
	double xE = p.momentum().E()/meanBeamMom;
	if(p.children()[0].pid()==sign*421 && 
	   p.children()[1].pid()==sign*211) {
	  decay = p.children()[1];
	}
	else if(p.children()[1].pid()==sign*421 && 
		p.children()[0].pid()==sign*211) {
	  decay = p.children()[0];
	}
	else
	  continue;
	// axis and ctheta
	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);
	// y and z axis
	Vector3 e1y = e1z.cross(axis).unit();
	Vector3 e1x = e1y.cross(e1z).unit();
	double phi = atan2(e1y.dot(axis1),e1x.dot(axis1));
	double w1 = 0.5*(5.*sqr(ctheta)-1.);
	double w2 = -1.25*(1.-sqr(ctheta))*cos(2.*phi);
	double w3 = -1.25*sqrt(2)*ctheta*sqrt(1.-sqr(ctheta))*cos(phi);
	// fill the hists by x_E
	for(unsigned int ix=0;ix<6;++ix) {
	  _p_rho00[ix]->fill(xE,w1);
	  _p_rho11[ix]->fill(xE,w2);
	  _p_rho10[ix]->fill(xE,w3);
	}
	_p_rho00[6]->fill(1.,w1);
	_p_rho11[6]->fill(1.,w2);
	_p_rho10[6]->fill(1.,w3);
	// using jet axis
	double pT = sqrt(sqr(sphericity.sphericityMajorAxis().dot(p.momentum().p3()))+
			 sqr(sphericity.sphericityMinorAxis().dot(p.momentum().p3())));
	Vector3 axis2;
	if(p.momentum().p3().dot(sphericity.sphericityAxis())>=0.) {
	  axis2 = sphericity.sphericityAxis();
	}
	else {
	  axis2 =-sphericity.sphericityAxis();
	}
	Vector3 e2y = e1z.cross(axis2).unit();
	Vector3 e2x = e2y.cross(e1z).unit();
	// alpha and beta
	phi = atan2(e2y.dot(axis1),e2x.dot(axis1));
	w1 = 0.5*(5.*sqr(ctheta)-1.);
	w2 = -1.25*(1.-sqr(ctheta))*cos(2.*phi);
	w3 = -1.25*sqrt(2)*ctheta*sqrt(1.-sqr(ctheta))*cos(phi);
	if(xE<0.4) continue;
	_p_rho00[7]->fill(1.,w1);
	_p_rho11[7]->fill(1.,w2);
	_p_rho10[7]->fill(1.,w3);
	if(pT<0.75) {
	  _p_rho00[7]->fill(2.,w1);
	  _p_rho11[7]->fill(2.,w2);
	  _p_rho10[7]->fill(2.,w3);
	}
	else {
	  _p_rho00[7]->fill(3.,w1);
	  _p_rho11[7]->fill(3.,w2);
	  _p_rho10[7]->fill(3.,w3);
	}
	if(sphericity.sphericity()>=0.1) {
	  _p_rho00[8]->fill(1.,w1);
	  _p_rho11[8]->fill(1.,w2);
	  _p_rho10[8]->fill(1.,w3);
	}
	else {
	  _p_rho00[8]->fill(2.,w1);
	  _p_rho11[8]->fill(2.,w2);
	  _p_rho10[8]->fill(2.,w3);
	}
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {

    }

    //@}


    /// @name Histograms
    //@{
    Profile1DPtr _p_rho00[9],_p_rho11[9],_p_rho10[9];
    //@}


  };


  // The hook for the plugin system
  DECLARE_RIVET_PLUGIN(HRS_1987_I250823);


}