rivet is hosted by Hepforge, IPPP Durham

Rivet analyses reference

CLEOII_1994_I371611

Decay asymmetry in $\Lambda^+_c\to\Lambda^0 e^+ \nu_e$
Experiment: CLEOII (CESR)
Inspire ID: 371611
Status: VALIDATED
Authors:
  • Peter Richardson
References:
  • Phys.Lett.B 323 (1994) 219-226
Beams: * *
Beam energies: ANY
Run details:
  • Any process producing Lambda_c+, original e+e-

Measurement of the decay asymmetry in $\Lambda^+_c\to\Lambda^0 e^+ \nu_e$ by CLEOII. While this result is superseeded by later CLEO measurements it is one of the few to present the anglular distribution as well as the fitted asymmetry parameter. The product of assymetries $\alpha_{\Lambda_c^+}\alpha_\Lambda$ is extracted as that is what is measured not $\alpha_{\Lambda_c^+}$ and there has been a significant change in $\alpha_\Lambda$ since this paper was published

Source code: CLEOII_1994_I371611.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
// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {


  /// @brief Lambda_c -> Lambda e+ nu_e asymmetry
  class CLEOII_1994_I371611 : public Analysis {
  public:

    /// Constructor
    DEFAULT_RIVET_ANALYSIS_CTOR(CLEOII_1994_I371611);


    /// @name Analysis methods
    //@{

    /// Book histograms and initialise projections before the run
    void init() {
      // Initialise and register projections
      declare(UnstableParticles(), "UFS" );
      
      // Book histograms
      book(_h_Lambda, 1,1,1);
    }

    void findChildren(Particle parent, int sign, unsigned int & npart,
		      Particles & lambda, Particles & e, Particles & nu) {
      for(const Particle & child : parent.children()) {
	if(child.pid()==sign*PID::LAMBDA) {
	  lambda.push_back(child);
	  ++npart;
	}
	else if(child.pid()==-sign*PID::EMINUS) {
	  e.push_back(child);
	  ++npart;
	}
	else if(child.pid()==sign*PID::NU_E) {
	  nu.push_back(child);
	  ++npart;
	}
	else if(!child.children().empty()) {
	  findChildren(child,sign,npart,lambda,e,nu);
	}
	else {
	  ++npart;
	}
      }
    }

    /// Perform the per-event analysis
    void analyze(const Event& event) {
      // loop over Lambda_c baryons
      for( const Particle& Lambdac : apply<UnstableParticles>(event, "UFS").particles(Cuts::abspid==4122)) {
	int sign = Lambdac.pid()/4122;
        Particles lambda,e,nu;
        unsigned int npart(0);
        findChildren(Lambdac,sign,npart,lambda,e,nu);
	if(npart!=3 || lambda.size()!=1 || e.size()!=1 || nu.size()!=1) continue;
	Particle baryon2;
	if(lambda[0].children()[0].pid()== sign*2212 && 
	   lambda[0].children()[1].pid()== -sign*211) {
	  baryon2 = lambda[0].children()[0];
	}
	else if(lambda[0].children()[1].pid()== sign*2212 && 
		lambda[0].children()[0].pid()== -sign*211) {
	  baryon2 = lambda[0].children()[1];
	}
	else
	  continue;
	// first boost to the Lambdac rest frame
	LorentzTransform boost1 = LorentzTransform::mkFrameTransformFromBeta(Lambdac.momentum().betaVec());
	FourMomentum pbaryon1 = boost1.transform(lambda[0].momentum());
	FourMomentum pbaryon2 = boost1.transform(baryon2  .momentum());
	// to lambda rest frame
	LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(pbaryon1.betaVec());
	Vector3 axis = pbaryon1.p3().unit();
	FourMomentum pp = boost2.transform(pbaryon2);
	// calculate angle
	double cTheta = pp.p3().unit().dot(axis);
	_h_Lambda->fill(cTheta);
      }
    }

    pair<double,double> calcAlpha(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 = 0.5*(bin.xMax()-bin.xMin());
	double bi = 0.5*ai*(bin.xMax()+bin.xMin());
	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() {
      //  asymmetry
      normalize(_h_Lambda);
      Scatter2DPtr _h_alpha;
      book(_h_alpha,2,1,1);
      pair<double,double> alpha = calcAlpha(_h_Lambda);
      _h_alpha->addPoint(0.5, alpha.first, make_pair(0.5,0.5), make_pair(alpha.second,alpha.second) );
    }

    //@}


    /// @name Histograms
    //@{
    Histo1DPtr _h_Lambda;
    //@}


  };


  DECLARE_RIVET_PLUGIN(CLEOII_1994_I371611);

}