Rivet analyses

D1(2420)0 and D2*(2460)0 decay angle distributions

Experiment: CLEO (CESR)

Inspire ID: 281039

Status: VALIDATED

Authors: - Peter Richardson

References: - Phys.Rev. D41 (1990) 774

Beams: e- e+

Beam energies: (5.2, 5.2)GeV

Run details: none listed

Measurement of the D1(2420)0 and D2*(2460)0 mesons at 10.5 GeV. The decay angle of the D+* with respect to the D1(2420)0 or D2*(2460)0 direction in the rest frame of the parent hadron, is measured. This gives information on the spin of the parent.

Source code:CLEO_1990_I281039.cc

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

namespace Rivet {


  /// @brief D_1 D*2 decay angle
  class CLEO_1990_I281039 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(CLEO_1990_I281039);


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

    /// Book histograms and initialise projections before the run
    void init() {

      // Initialise and register projections
      declare(UnstableParticles(), "UFS");

      // Book histograms
      book(_h_D1, 1, 1, 1);
      book(_h_D2, 1, 1, 2);
    }

    /// Recursively walk the decay tree to find decay products of @a p
    void findDecayProducts(Particle mother, Particles& dstar, Particles& pi, unsigned int& ncount) {
      for (const Particle& p : mother.children()) {
        if (p.abspid() == 413)
          dstar.push_back(p);
        else if (p.abspid() == 211)
          pi.push_back(p);
        ncount += 1;
      }
    }

    /// Perform the per-event analysis
    void analyze(const Event& event) {
      for (const Particle& p :
           apply<UnstableParticles>(event, "UFS").particles(Cuts::abspid == 425 || Cuts::abspid == 10423)) {
        // decay products
        Particles dstar, pi;
        unsigned int ncount = 0;
        findDecayProducts(p, dstar, pi, ncount);
        if (ncount != 2 || dstar.size() != 1 || pi.size() != 1) continue;
        if (dstar[0].pid() / p.pid() < 0) continue;
        LorentzTransform boost = LorentzTransform::mkFrameTransformFromBeta(p.momentum().betaVec());
        Vector3 axis = boost.transform(dstar[0].momentum()).p3().unit();
        double cosL = axis.dot(p.momentum().p3().unit());
        // decay angles
        if (p.abspid() == 425)
          _h_D2->fill(cosL);
        else
          _h_D1->fill(cosL);
      }
    }


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

      normalize(_h_D1);
      normalize(_h_D2);
    }

    /// @}


    /// @name Histograms
    /// @{
    Histo1DPtr _h_D1, _h_D2;
    /// @}
  };


  RIVET_DECLARE_PLUGIN(CLEO_1990_I281039);


}