Rivet analyses

title: CLEO_1986_I230961

$J/\psi$ spectrum in $\Upsilon(4S)$ decays

Experiment: CLEO (CESR)

Inspire ID: 230961

Status: VALIDATED

Authors: - Peter Richardson

References: - Phys.Rev.D 34 (1986) 3279

Beams: * *

Beam energies: ANY

Run details: - Any process producing Upsilon(4S), originally e+e-

Measurement of the $J/\psi$ spectrum in $\Upsilon(4S)$ decays by the CLEO collaboration.

Source code:CLEO_1986_I230961.cc

```c++ // -- C++ --

include "Rivet/Analysis.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief J/psi spectrum in Upsilon(4S) decays class CLEO_1986_I230961 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(CLEO_1986_I230961);


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

/// Book histograms and initialise projections before the run
void init() {
  // projections
  declare(UnstableParticles(Cuts::pid == 300553), "UFS");
  // histos
  book(_h, 2, 1, 1);
}

/// 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 == 443) {
      unstable.push_back(p);
    }
    else if (!p.children().empty()) {
      findDecayProducts(p, unstable);
    }
  }
}


/// Perform the per-event analysis
void analyze(const Event& event) {
  const UnstableParticles& ufs = apply<UnstableParticles>(event, "UFS");
  for (const Particle& ups : ufs.particles()) {
    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.mom().betaVec());
    }
    for (const Particle& p : unstable) {
      const double modp = cms_boost.transform(p.mom()).p3().mod();
      _h->fill(modp);
    }
  }
}


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

/// @}


/// @name Histograms
/// @{
Histo1DPtr _h;
/// @}

};

RIVET_DECLARE_PLUGIN(CLEO_1986_I230961);

} ```