Rivet analyses

Spectra and decay distributions for D1(2420)0 and D2*(2460)0 production in e+e− collisions at 10 GeV

Experiment: ARGUS (DORIS)

Inspire ID: 280943

Status: VALIDATED

Authors: - Peter Richardson

References: - Phys.Lett. B232 (1989) 398-404

Beams: e- e+

Beam energies: (5.0, 5.0)GeV

Run details: - e+e- to hadrons

Measurements of the scaled momentum spectrum for D1(2420)0 and D2*(2460)0 production in e+e− collisions at 10 GeV. The decays D1(2420)0, D2*(2460)0 → D*+π− → D0π+π− were used and the helicity angle, i.e. the angle between the two pions in the rest frame of the D* are is measured.

Source code:ARGUS_1989_I280943.cc

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

namespace Rivet {


  /// @brief D_1 and D_2 spectra and decay distributions
  class ARGUS_1989_I280943 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(ARGUS_1989_I280943);


    /// @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_rate    ,1,1,1);
      book(_h_D2_rate    ,1,1,2);
      book(_h_D1_x       ,4,1,1);
      book(_h_D2_x       ,4,1,2);
      book(_h_D1_alpha   ,3,1,1);
      book(_h_D2_alpha   ,3,1,2);
    }

    /// Recursively walk the decay tree to find decay products of @a p
    void findDecayProducts(Particle mother, Particles & dstar, Particles & d0, Particles & pi,unsigned int & ncount) {
      for (const Particle & p: mother.children()) {
        if(p.abspid()==413)
          dstar.push_back(p);
        else if(p.abspid()==421)
          d0.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)) {
    const double xp = 2.*p.p3().mod()/sqrtS();
    // spectra
    if(p.abspid()==425)
      _h_D2_x->fill(xp);
    else
      _h_D1_x->fill(xp);
    // decay products
    // first od D_1,D_2
    Particles dstar,d0,pi;
    unsigned int ncount=0;
    findDecayProducts(p,dstar,d0, pi,ncount);
    if(ncount!=2 || dstar.size()!=1 || pi.size()!=1 || d0.size()!=0 ) continue;
    if(dstar[0].pid()/p.pid()<0) continue;
    if(p.abspid()==425)
      _h_D2_rate->fill(10);
    else
      _h_D1_rate->fill(10);
    Particle p2 = dstar[0];
    LorentzTransform boost = LorentzTransform::mkFrameTransformFromBeta(p2.momentum().betaVec());
    Vector3 d1 = boost.transform(pi[0].momentum()).p3().unit();
    // then of D*
    ncount=0;
    dstar.clear();
    d0.clear();
    pi.clear();
    findDecayProducts(p2,dstar,d0, pi,ncount);
    if(ncount!=2 || dstar.size()!=0 || pi.size()!=1 || d0.size()!=1 ) continue;
    if(pi[0].pid()/p2.pid()<0) continue;
    Vector3 d2 = boost.transform(pi[0].momentum()).p3().unit();
    double cosAlpha  = abs(d1.dot(d2));
    // decay angles
    if(p.abspid()==425)
      _h_D2_alpha->fill(cosAlpha);
    else
      _h_D1_alpha->fill(cosAlpha);
      }
    }


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

      normalize(_h_D1_x);
      normalize(_h_D2_x);
      normalize(_h_D1_alpha);
      normalize(_h_D2_alpha);
      scale(_h_D1_rate,crossSection()/picobarn/sumOfWeights());
      scale(_h_D2_rate,crossSection()/picobarn/sumOfWeights());

    }

    /// @}


    /// @name Histograms
    /// @{
    BinnedHistoPtr<int> _h_D1_rate, _h_D2_rate;
    Histo1DPtr _h_D1_x, _h_D2_x;
    Histo1DPtr _h_D1_alpha, _h_D2_alpha;
    const int Ecms = 10;
    /// @}


  };


  RIVET_DECLARE_PLUGIN(ARGUS_1989_I280943);


}