Rivet analyses

Mass distributions in Λc+ → ΛK̄0K+

Experiment: BABAR (PEP-II)

Inspire ID: 722213

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - hep-ex/0607043 [hep-ex]

Beams: * *

Beam energies: ANY

Run details: - Any process producing Lambda_c+ mesons

Measurement of the mass distributions in the decay Λc+ → ΛK̄0K+, together with angular distributions in the Ξ(1690) region. The data were read from the plots in the paper but have been corrected for efficiency/acceptance but not resolution.

Source code:BABAR_2006_I722213.cc

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

namespace Rivet {


  /// @brief Lambda_c+ -> Lambda Kbar0 K+
  class BABAR_2006_I722213 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BABAR_2006_I722213);


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

    /// Book histograms and initialise projections before the run
    void init() {
      // Initialise and register projections
      UnstableParticles ufs = UnstableParticles(Cuts::abspid==4122);
      declare(ufs, "UFS");
      DecayedParticles LAMBDAC(ufs);
      LAMBDAC.addStable(PID::PI0);
      LAMBDAC.addStable(PID::K0S);
      LAMBDAC.addStable(PID::ETA);
      LAMBDAC.addStable(PID::LAMBDA);
      LAMBDAC.addStable(-PID::LAMBDA);
      declare(LAMBDAC, "LAMBDAC");
      // histograms
      for (size_t ix=0; ix<3; ++ix) {
        book(_h_mass[ix], 1, 1, 1+ix);
      }
      for (size_t ix=0; ix<2; ++ix) {
        book(_h_ctheta[ix], 2, 1, 1+ix);
      }
    }


    /// Perform the per-event analysis
    void analyze(const Event& event) {
      static const map<PdgId,unsigned int> & mode   = { { PID::LAMBDA,1}, { 321,1}, { 310,1}};
      static const map<PdgId,unsigned int> & modeCC = { {-PID::LAMBDA,1}, {-321,1}, { 310,1}};
      DecayedParticles LAMBDAC = apply<DecayedParticles>(event, "LAMBDAC");
      // loop over particles
      for (size_t ix=0; ix<LAMBDAC.decaying().size(); ++ix) {
        int sign = 1;
        if (LAMBDAC.decaying()[ix].pid()>0 && LAMBDAC.modeMatches(ix,3,mode)) {
          sign=1;
        }
        else if  (LAMBDAC.decaying()[ix].pid()<0 && LAMBDAC.modeMatches(ix,3,modeCC)) {
          sign=-1;
        }
        else {
          continue;
        }
        const Particle& lam = LAMBDAC.decayProducts()[ix].at( sign*PID::LAMBDA)[0];
        const Particle& K0  = LAMBDAC.decayProducts()[ix].at( 310)[0];
        const Particle& Kp  = LAMBDAC.decayProducts()[ix].at( sign*321)[0];
        double mLamK = (lam.mom()+K0.mom()).mass();
        _h_mass[0]->fill(mLamK);
        _h_mass[1]->fill((Kp .mom()+K0.mom()).mass()-Kp.mass()-K0.mass());
        _h_mass[2]->fill((lam.mom()+Kp.mom()).mass()-Kp.mass()-lam.mass());
        // take Xi(1690) to be any resonance in mass region
        if (mLamK<1.6725 || mLamK>1.6975) continue;
        if (LAMBDAC.decaying()[ix].children().size()!=2) continue;
        if (LAMBDAC.decaying()[ix].children()[0].abspid()!=321 &&
            LAMBDAC.decaying()[ix].children()[1].abspid()!=321) continue;
        LorentzTransform boost1 = LorentzTransform::mkFrameTransformFromBeta(LAMBDAC.decaying()[ix].mom().betaVec());
        FourMomentum pbaryon1 = boost1.transform(LAMBDAC.decaying()[ix].mom());
        FourMomentum pbaryon2 = boost1.transform(lam.mom());
        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_ctheta[0]->fill(cTheta);
        _h_ctheta[1]->fill(cTheta);
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      normalize(_h_mass);
      normalize(_h_ctheta);
    }

    /// @}


    /// @name Histograms
    /// @{
    Histo1DPtr _h_mass  [3];
    Histo1DPtr _h_ctheta[2];
    /// @}


  };


  RIVET_DECLARE_PLUGIN(BABAR_2006_I722213);

}