Rivet analyses

title: CLEOIII_2004_I654639

$J/\psi$ spectrum in $\Upsilon(1S)$ decays

Experiment: CLEOIII (CESR)

Inspire ID: 654639

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.D 70 (2004) 072001

Beams: e+ e-

Beam energies: (4.7, 4.7)GeV

Run details: - e+e- > hadrons at Upslion(1S)

Measurement of the $J/\psi$ spectrum in $\Upsilon(1S)$ decays. The corrected data were read from the figures in the paper.

Source code:CLEOIII_2004_I654639.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief J/psi spectrum in Upsilon(1S) decay class CLEOIII_2004_I654639 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(CLEOIII_2004_I654639);


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

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

/// 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);
    }
    if (!p.children().empty()) {
      findDecayProducts(p, unstable);
    }
  }
}

/// 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()) {
    // boost to rest frame
    LorentzTransform boost;
    if (ups.p3().mod() > 1 * MeV) {
      boost = LorentzTransform::mkFrameTransformFromBeta(ups.momentum().betaVec());
    }
    // find  psi
    Particles unstable;
    findDecayProducts(ups, unstable);
    // loop over psi/psi(2S)
    for (const Particle& psi : unstable) {
      double Pmax = 0.5 * (sqr(ups.mass()) - sqr(psi.mass())) / ups.mass();
      const FourMomentum p2 = boost.transform(psi.momentum());
      const double xP = p2.p3().mod() / Pmax;
      _h[0]->fill(xP);
      _h[1]->fill(xP);
    }
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  scale(_h, crossSection() / sumOfWeights() / picobarn);
}

/// @}


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

};

RIVET_DECLARE_PLUGIN(CLEOIII_2004_I654639);

} ```