Rivet analyses

title: CUSB_1984_I204307

Direct Photon Spectrum in $\Upsilon(1,2)$ 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 $\Upsilon(1,2)$ 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++ // -- 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);

} ```