Rivet analyses

Direct Photon Spectrum in Υ(1, 2) decays

Experiment: CUSB (CESR)

Inspire ID: 204307

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Lett.B 138 (1984) 225-229

Beams: * *

Beam energies: ANY

Run details: - Any process producing Upsilon mesons, original e+e- collisions

Measurement of the photon spectrum in Υ(1, 2) decays by CUSB. The spectrum was read from the figures in the paper but is corrected for efficiency/resolution.

Source code:CUSB_1984_I204307.cc

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

namespace Rivet {


  /// @brief Photon spectrum in Upsilon(1,2S) decays
  class CUSB_1984_I204307 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(CUSB_1984_I204307);


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

    /// Book histograms and initialise projections before the run
    void init() {
      // projections
      declare(UnstableParticles(Cuts::pid==553 || Cuts::pid==100553), "UFS");
      // histos
      for (unsigned int ix=0; ix<2; ++ix) {
          book(_h[ix],1+ix,1,1);
      }
    }


    /// Perform the per-event analysis
    void analyze(const Event& event) {
      // Find the Upsilons among the unstables
      for (const Particle& ups : apply<UnstableParticles>(event, "UFS").particles()) {
        unsigned int iups = ups.pid()/100000;
        unsigned int nhadron(0);
        Particles photons;
        for (const Particle& child : ups.children()) {
          if (PID::isHadron(child.pid())) {
            ++nhadron;
          }
          else if(child.pid()==PID::PHOTON) {
            photons.push_back(child);
          }
        }
        if (nhadron==0 || photons.empty()) continue;
        LorentzTransform boost;
        if (ups.p3().mod() > 1*MeV) {
          boost = LorentzTransform::mkFrameTransformFromBeta(ups.mom().betaVec());
        }
        for (const Particle& gamma : photons) {
          const double E = boost.transform(gamma.mom()).E();
          // E = randnorm(E,0.21*sqrt(E));
          _h[iups]->fill(2.*E/ups.mass());
        }
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      normalize(_h, 1.0, false);
    }

    /// @}


    /// @name Histograms
    /// @{
    Histo1DPtr _h[2];
    /// @}


  };


  RIVET_DECLARE_PLUGIN(CUSB_1984_I204307);

}