Rivet analyses

Charged particle multiplicity and 2nd Fox-Wolfram moment in χb0, 1, 2′ Decays

Experiment: CLEOII (CUSB)

Inspire ID: 32611

Status: UNVALIDATED

Authors: - Peter Richardson

References: - Phys.Rev. D46 (1992) 4822-4827

Beams: * *

Beam energies: ANY

Run details: - Any process producing chi_b(2P), original e+e-> Upsilon(3S)

Measurement of the average charged particle multiplicity, and the charged multiplicity distribution in χb0, 1, 2′ Decays. In addition the average 2nd Fox-Wolfram moment, and its distribution is also measured.

Source code:CLEOII_1992_I32611.cc

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

namespace Rivet {


  /// @brief chi_b(2S) decays
  class CLEOII_1992_I32611 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(CLEOII_1992_I32611);


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

    /// Book histograms and initialise projections before the run
    void init() {
      // Initialise and register projections
      declare(UnstableParticles(), "UFS");
      // Book histograms
      // averages
      book(_h_N_aver, 1, 1, 1);
      book(_h_R2_aver, 1, 1, 2);
      // dists
      _h_N = {Histo1DPtr(), Histo1DPtr(), Histo1DPtr()};
      _h_R2 = {Histo1DPtr(), Histo1DPtr(), Histo1DPtr()};
      book(_h_N[0], 2, 1, 1);
      book(_h_N[1], 2, 1, 2);
      book(_h_N[2], 2, 1, 3);
      book(_h_R2[0], 3, 1, 1);
      book(_h_R2[1], 3, 1, 2);
      book(_h_R2[2], 3, 1, 3);
    }

    void findDecayProducts(Particle parent, Particles& children, unsigned int& nCharged) {
      for (const Particle& p : parent.children()) {
        if (p.children().empty()) {
          if (isCharged(p)) ++nCharged;
          children.push_back(p);
        }
        else
          findDecayProducts(p, children, nCharged);
      }
    }

    /// Perform the per-event analysis
    void analyze(const Event& event) {
      Particles chib = apply<UnstableParticles>(event, "UFS")
                           .particles(Cuts::pid == 110551 or Cuts::pid == 120553 or Cuts::pid == 100555);
      for (const Particle& p : chib) {
        unsigned int iHist = (p.pid() % 10) / 2;
        unsigned int nCharged(0);
        Particles children;
        findDecayProducts(p, children, nCharged);
        // ncharged
        _h_N[iHist]->fill(nCharged);
        _h_N_aver->fill(iHist, nCharged);
        // R_2
        LorentzTransform boost = LorentzTransform::mkFrameTransformFromBeta(p.momentum().betaVec());
        vector<FourMomentum> mom;
        mom.reserve(children.size());
        for (const Particle& p2 : children) {
          mom.push_back(boost.transform(p2.momentum()));
        }
        // compute R2
        double H0(0.), H2(0.);
        for (const FourMomentum& p1 : mom) {
          double mod1 = p1.p3().mod();
          Vector3 axis = p1.p3().unit();
          for (const FourMomentum& p2 : mom) {
            double mod2 = p2.p3().mod();
            double cTheta = axis.dot(p2.p3().unit());
            H0 += mod1 * mod2;
            H2 += mod1 * mod2 * 0.5 * (3. * sqr(cTheta) - 1.);
          }
        }
        double R2 = H2 / H0;
        _h_R2[iHist]->fill(R2);
        _h_R2_aver->fill(iHist, R2);
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      for (unsigned int ix = 0; ix < 3; ++ix) {
        normalize(_h_N[ix]);
        normalize(_h_R2[ix]);
      }
    }

    /// @}


    /// @name Histograms
    /// @{
    vector<Histo1DPtr> _h_N, _h_R2;
    BinnedProfilePtr<int> _h_N_aver, _h_R2_aver;
    /// @}
  };


  RIVET_DECLARE_PLUGIN(CLEOII_1992_I32611);

}