Rivet analyses

Spectrum and decay angle for D20 production in e+e− at 10 GeV in the continuum

Experiment: ARGUS (DORIS)

Inspire ID: 268577

Status: VALIDATED

Authors: - Peter Richardson

References: - Phys.Lett. B221 (1989) 422-426

Beams: e- e+

Beam energies: (5.0, 5.0)GeV

Run details: - e+e− analysis near the Υ resonances

Measurement of the D2*(2460)0 spectrum in e+e− collisions at 10 GeV. The decay angle of the D+ with respect to the D2*(2460)0 direction in the rest frame of the parent hadron, this gives information on the spin of the parent, is also measured.

Source code:ARGUS_1989_I268577.cc

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

namespace Rivet {


  /// @brief D*2 spectrum and decay angle
  class ARGUS_1989_I268577 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(ARGUS_1989_I268577);


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

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

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

      // Book histograms
      book(_h_rate     , 1, 1, 1);
      book(_h_D2_x     , 2, 1, 1);
      book(_h_D2_ctheta, 3, 1, 1);
    }


   /// Recursively walk the decay tree to find decay products of @a p
   void findDecayProducts(Particle mother, Particles & d, Particles & pi, unsigned int & ncount) {
     for (const Particle & p: mother.children()) {
       if (p.abspid()==411)
         d.push_back(p);
       else if (p.abspid()==211)
         pi.push_back(p);
       ncount +=1;
     }
   }

    /// Perform the per-event analysis
    void analyze(const Event& event) {

      if (sedges.empty()) {
        sedges = _h_D2_x->xEdges();
      }

      const UnstableParticles& ufs = apply<UnstableParticles>(event, "UFS");
      for (const Particle& p : ufs.particles(Cuts::abspid==425)) {
        const double xp = 2.*p.p3().mod()/sqrtS();
        const size_t idx = axisMap.index(xp)-1;
        _h_D2_x->fill(sedges[idx]);
        // decay products
        Particles d,pi;
        unsigned int ncount=0;
        findDecayProducts(p,d,pi,ncount);
        if(ncount!=2 || d.size()!=1 || pi.size()!=1) continue;
        if(d[0].pid()/p.pid()<0) continue;
        LorentzTransform boost = LorentzTransform::mkFrameTransformFromBeta(p.momentum().betaVec());
        Vector3 axis = boost.transform(pi[0].momentum()).p3().unit();
        double cosL  = axis.dot(p.momentum().p3().unit());
        // decay angles
        _h_D2_ctheta->fill(cosL);
        _h_rate->fill(10);
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      normalize(_h_D2_x);
      for(auto & b : _h_D2_x->bins()) {
        b.scaleW(1./axisMap.width(b.index()));
      }
      normalize(_h_D2_ctheta);
      // br of D mode used from PDG2018
      const double br = 0.0898;
      scale(_h_rate,br/sumOfWeights()*crossSection()/picobarn);
    }

    /// @}


    /// @name Histograms
    /// @{
    BinnedHistoPtr<int> _h_rate;
    BinnedHistoPtr<string> _h_D2_x;
    Histo1DPtr _h_D2_ctheta;
    vector<string> sedges;
    YODA::Axis<double> axisMap{0.0, 0.5, 0.6, 0.7, 0.85, 1.0};
    /// @}


  };


  RIVET_DECLARE_PLUGIN(ARGUS_1989_I268577);


}