Rivet analyses

title: BELLE_2016_I1454405

$J/\psi$ and $\psi(2S)$ spectrum in $\Upsilon(1S)$ decays

Experiment: BELLE (KEKB)

Inspire ID: 1454405

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.D 93 (2016) 11, 112013

Beams: * *

Beam energies: ANY

Run details: - Any process producing Upsilon(1S) originally e+e-

Measurement of the scaled momentum of $J/\psi$ and $\psi(2S)$ in $\Upsilon(1S)$ decays

Source code:BELLE_2016_I1454405.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief J/psi and psi(2S) in Upsilon(1S) decays class BELLE_2016_I1454405 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BELLE_2016_I1454405);


/// @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)
    for (unsigned int iy = 0; iy < 2; ++iy) book(_h[ix][iy], 1, 1 + ix, 1 + iy);
  book(_nUps, "TMP/nUps");
}

/// 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 || id == 100443) {
      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()) {
    _nUps->fill();
    // boost to rest frame
    LorentzTransform boost;
    if (ups.p3().mod() > 1 * MeV)
      boost = LorentzTransform::mkFrameTransformFromBeta(ups.momentum().betaVec());
    // find  psi/psi(2S)
    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;
      if (psi.pid() == 443) {
        _h[0][0]->fill(xP);
        _h[1][0]->fill(xP);
      }
      else {
        _h[0][1]->fill(xP);
        _h[1][1]->fill(xP);
      }
    }
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  for (unsigned int ix = 0; ix < 2; ++ix)
    for (unsigned int iy = 0; iy < 2; ++iy) scale(_h[ix][iy], 1e4 / *_nUps);
}

/// @}


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

};

RIVET_DECLARE_PLUGIN(BELLE_2016_I1454405);

} ```