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);


}