Rivet analyses

Spectra of η′ mesons in Υ(1S) decays

Experiment: CLEO-II (CESR)

Inspire ID: 601701

Status: VALIDATED

Authors: - Peter Richardson

References: - Phys.Rev. D67 (2003) 052003

Beams: * *

Beam energies: ANY

Run details: - Any process producing Upslion 1S, original e+e−

Measurement of the inclusive production of the η′ mesons in Υ(1S) decays by the CLEO-II experiment. In principle this measurement is superseeded, however the newer result (CLEOIII_2006_I728679) did not include numerical values which were read from the plots and therefore we keep this measurement.

Source code:CLEOII_2002_I601701.cc

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

namespace Rivet {


  /// @brief eta' production in Upsilon(1S) decays
  class CLEOII_2002_I601701 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(CLEOII_2002_I601701);


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

    /// Book histograms and initialise projections before the run
    void init() {
      declare(UnstableParticles(), "UFS");

      book(_hist, 1, 1, 3);
      book(_mult, 2, 1, 3);
      book(_weightSum,"TMP/weightSum");

    }

    /// Recursively walk the decay tree to find decay products of @a p
    void findDecayProducts(Particle mother, Particles& unstable) {
      for(const Particle & p: mother.children()) {
        const int id = abs(p.pid());
    if ( id == 331 ) {
      unstable.push_back(p);
    }
    else if(!p.children().empty())
      findDecayProducts(p, unstable);
      }
    }

    /// Perform the per-event analysis
    void analyze(const Event& event) {
      // find the Upsilon(1S) mesons
      const UnstableParticles& ufs = apply<UnstableParticles>(event, "UFS");
      Particles upsilons = ufs.particles(Cuts::pid==553);
      if(upsilons.empty()) vetoEvent;
      // loop over them
      for (const Particle& ups : upsilons) {
    _weightSum->fill();
    Particles unstable;
    // Find the decay products we want
    findDecayProducts(ups,unstable);
    LorentzTransform cms_boost;
    if (ups.p3().mod() > 0.001)
      cms_boost = LorentzTransform::mkFrameTransformFromBeta(ups.momentum().betaVec());
    double mass = ups.mass();
    _mult->fill(unstable.size());
    // fill the spectrum
    for( const Particle & p : unstable) {
      FourMomentum p2 = cms_boost.transform(p.momentum());
      double xp = 2.*p2.E()/mass;
      _hist->fill(xp);
    }
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      // spectrum
      if (_weightSum->val() > 0.)
        scale(_hist, 1. / *_weightSum);
      // BR
      scale(_mult,1./ *_weightSum);
    }

    /// @}


    /// @name Histograms
    /// @{
    Histo1DPtr _hist;
    CounterPtr _mult;
    CounterPtr _weightSum;
    /// @}


  };


  RIVET_DECLARE_PLUGIN(CLEOII_2002_I601701);

}