Rivet analyses

Decay asymmetries in Λ_c⁺ → Λ⁰π⁺ and Λ_c⁺ → Σ⁺π⁰

Experiment: CLEO (CESR)

Inspire ID: 392704

Status: VALIDATED

Authors: - Peter Richardson

References: - Phys.Lett. B350 (1995) 256-262

Beams: * *

Beam energies: ANY

Run details: - Any process producing Lambda_c baryons

Measurement of the decay asymmetries in Λ_c⁺ → Λ⁰π⁺ and Λ_c⁺ → Σ⁺π⁰ by the CLEO experiment. The asymmetry parameter is extracted by fitting to normalised angular distribution. N.B. the product of the asymmetry parameters for the Λ_c and daughter baryon is implemented as this is what is measured, rather than the extracted parameter for the Λ_c which relies on other measurements of the parameter for the daughter baryon. This analysis is useful for testing spin correlations in hadron decays.

Source code:`CLEO_1995_I392704.cc`

// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {


  /// @brief Lambda_c -> Lambda pi and Lambda_c _> Sigma+ pi0 asymmetries
  class CLEO_1995_I392704 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(CLEO_1995_I392704);


    /// @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);
      book(_h_Sigma , 2,1,1);
    }


    /// 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;
    if(Lambdac.children().size()!=2) continue;
    Particle baryon1;
    bool lambda=true;
    if(Lambdac.children()[0].pid()==sign*3122 &&
       Lambdac.children()[1].pid()==sign*211) {
      baryon1 = Lambdac.children()[0];
    }
    else if(Lambdac.children()[1].pid()==sign*3122 &&
        Lambdac.children()[0].pid()==sign*211) {
      baryon1 = Lambdac.children()[1];
    }
    else if(Lambdac.children()[0].pid()==sign*3222 &&
        Lambdac.children()[1].pid()==111) {
      baryon1 = Lambdac.children()[0];
      lambda=false;
    }
    else if(Lambdac.children()[1].pid()==sign*3222 &&
        Lambdac.children()[0].pid()==111) {
      baryon1 = Lambdac.children()[0];
      lambda=false;
    }
    else
      continue;
    int idMeson = lambda ? -sign*211 : 111;
    Particle baryon2;
    if(baryon1.children()[0].pid()== sign*2212 &&
       baryon1.children()[1].pid()== idMeson) {
      baryon2 = baryon1.children()[0];
    }
    else if(baryon1.children()[1].pid()== sign*2212 &&
        baryon1.children()[0].pid()== idMeson) {
      baryon2 = baryon1.children()[1];
    }
    else
      continue;
    // first boost to the Lambdac rest frame
    LorentzTransform boost1 = LorentzTransform::mkFrameTransformFromBeta(Lambdac.momentum().betaVec());
    FourMomentum pbaryon1 = boost1.transform(baryon1.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);
    if(lambda)
      _h_Lambda->fill(cTheta);
    else
      _h_Sigma->fill(cTheta);
      }
    }

    pair<double,double> calcAlpha(Histo1DPtr hist) {
      if(hist->numEntries()==0.) return make_pair(0.,0.);
      double sum1(0.),sum2(0.);
      for (const auto& bin : hist->bins() ) {
        double Oi = bin.sumW();
        if(Oi==0.) continue;
        double ai = 0.5*(bin.xMax()-bin.xMin());
        double bi = 0.5*ai*(bin.xMax()+bin.xMin());
        double Ei = bin.errW();
        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() {
      // Lambda_c -> Lambda pi+
      normalize(_h_Lambda);
      Estimate0DPtr _h_alpha1;
      book(_h_alpha1,3,1,1);
      pair<double,double> alpha = calcAlpha(_h_Lambda);
      _h_alpha1->set(alpha.first, alpha.second);
      // Lambda_c -> Sigma+ pi0
      normalize(_h_Sigma);
      Estimate0DPtr _h_alpha2;
      book(_h_alpha2,4,1,1);
      alpha = calcAlpha(_h_Sigma);
      _h_alpha2->set(alpha.first, alpha.second);
    }

    /// @}


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


  };


  RIVET_DECLARE_PLUGIN(CLEO_1995_I392704);

}

Rivet analyses

Decay asymmetries in Λc+ → Λ0π+ and Λc+ → Σ+π0

Source code:CLEO_1995_I392704.cc

Decay asymmetries in Λ_c⁺ → Λ⁰π⁺ and Λ_c⁺ → Σ⁺π⁰

Source code:`CLEO_1995_I392704.cc`