Rivet analyses

Decay asymmetries in the decay of Ξ*(1530)0 baryons produced in the decay of Λc+ baryons

Experiment: BABAR (PEP-II)

Inspire ID: 781294

Status: VALIDATED

Authors: - Peter Richardson

References: - Phys.Rev.D 78 (2008) 034008

Beams: * *

Beam energies: ANY

Run details: - Any process producing Lambda_c+ baryons

Measurement of decay asymmetries in Λc+ → Ξ*(1530)0K+ followed by Ξ*(1530)0Ξ−π+ decays by the BaBaR experiment.

Source code:BABAR_2008_I781294.cc

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

namespace Rivet {


  /// @brief Xi* decay asymmetries
  class BABAR_2008_I781294 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BABAR_2008_I781294);


    /// @name Analysis methods
    /// @{

    /// Book histograms and initialise projections before the run
    void init() {
      // Initialise and register projections
      declare(UnstableParticles(), "UFS" );
      // book histos
      book(_h_ctheta,1,1,1);
      book(_h_P0    ,2,1,1);
      book(_h_P2    ,2,1,2);
      book(_wgtSum,"/TMP/WSUM");
    }

    void findChildren(const Particle &p, int & sign,
              unsigned int & nprod, Particles & Xi, Particles &pi,Particles &K) {
      for(const Particle & child : p.children()) {
    if(child.pid()==sign*3312) {
      Xi.push_back(child);
      ++nprod;
    }
    else if(child.pid()==211) {
      pi.push_back(child);
      ++nprod;
    }
    else if(child.pid()==321) {
      K.push_back(child);
      ++nprod;
    }
    else if(child.children().empty()) {
      ++nprod;
    }
    else {
      findChildren(child,sign,nprod,Xi,pi,K);
    }
      }
    }

    /// Perform the per-event analysis
    void analyze(const Event& event) {
      // loop over Lambda_c
      for(const Particle& baryon : apply<UnstableParticles>(event, "UFS").particles(Cuts::abspid==4122)) {
    int sign = baryon.pid()/baryon.abspid();
    Particles Xi,pi,K;
    unsigned int nprod(0);
    findChildren(baryon,sign,nprod,Xi,pi,K);
    // check Lambda_c -> Xi- pi+ K+ decya mode
    if(nprod!=3||Xi.size()!=1||pi.size()!=1||K.size()!=1) continue;
    // first boost to the Lambda_c rest frame
    LorentzTransform boost1 = LorentzTransform::mkFrameTransformFromBeta(baryon.momentum().betaVec());
    FourMomentum pbaryon1 = Xi[0].momentum()+pi[0].momentum();
    pbaryon1              = boost1.transform(pbaryon1);
    FourMomentum pbaryon2 = boost1.transform(Xi[0].momentum());
    // to Xi* 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);
    double mass = pbaryon1.mass();
    if(mass>1.5 && mass< 1.65)
      _h_ctheta->fill(cTheta);
    _h_P0->fill(mass);
    _h_P2->fill(mass,0.5*(3.*sqr(cTheta)-1.));
    _wgtSum->fill();
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      normalize(_h_ctheta);
      normalize(_h_P0,1.,false);
      normalize(_h_P2,1.,false);
    }
    /// @}


    /// @name Histograms
    /// @{
    Histo1DPtr _h_ctheta, _h_P0,_h_P2;
    CounterPtr _wgtSum;
    /// @}


  };


  RIVET_DECLARE_PLUGIN(BABAR_2008_I781294);

}