Rivet analyses

title: CDF_1997_I440446

$J/\psi$ production from $\chi_c$ decays at 1.8 TeV

Experiment: CDF (Tevatron)

Inspire ID: 440446

Status: VALIDATED

Authors: - Peter Richardson

References: - Phys.Rev.Lett. 79 (1997) 578-583, 1997.

Beams: p- p+

Beam energies: (900.0, 900.0)GeV

Run details: - J/psi and chi_c production

Measurement of the fraction of prompt $J/\psi$ produced in $\chi_c$ meson decays by the CDF collaboration.

Source code:CDF_1997_I440446.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief J/psi from chi_c decays class CDF_1997_I440446 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(CDF_1997_I440446);


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

/// Book histograms and initialise projections before the run
void init() {
  declare(UnstableParticles(), "UFS");
  const YODA::BinnedEstimate<int>& ref = refData<YODA::BinnedEstimate<int>>(1, 1, 1);
  book(_h_total[0], "TMP/h_chi", ref);
  book(_h_total[1], "TMP/h_psi", ref);
  for (unsigned int ix = 0; ix < 3; ++ix) {
    book(_h_psi[ix], 2 + ix, 1, 1);
  }
  _axis = YODA::Axis<double>({5., 5.5, 6., 6.5, 7., 8., 9., 10., 12., 14., 17., 20.});
}


/// Perform the per-event analysis
void analyze(const Event& event) {
  if (_edges.empty()) _edges = _h_psi[0]->xEdges();

  // Final state of unstable particles to get particle spectra
  const UnstableParticles& ufs = apply<UnstableParticles>(event, "UFS");
  // first J/psi for denominator
  for (const Particle& p : ufs.particles(Cuts::pid == 443)) {
    if (p.fromBottom()) continue;
    const double abseta = p.abseta();
    const double xp = p.perp();
    if (xp < 4. || abseta > 0.6) continue;
    _h_total[1]->fill(1800);
    // from those for higher charmonium
    Particle parent = p.parents()[0];
    if (parent.pid() == 100443 || parent.pid() == 20443 || parent.pid() == 445) continue;
    _h_psi[0]->fill(disc(xp));
  }
  // chi_1 and chi_2 for numerator
  for (const Particle& p : ufs.particles(Cuts::pid == 20443 || Cuts::pid == 100443 || Cuts::pid == 445)) {
    if (p.fromBottom()) continue;
    Particle Jpsi;
    bool found(false);
    for (const Particle& child : p.children()) {
      if (child.pid() == 443) {
        found = true;
        Jpsi = child;
      }
    }
    if (!found) continue;
    double abseta = Jpsi.abseta();
    double xp = Jpsi.perp();
    if (xp < 4. || abseta > 0.6) continue;
    if (p.pid() == 100443) {
      _h_psi[2]->fill(disc(xp));
    }
    else {
      _h_psi[1]->fill(disc(xp));
      _h_total[0]->fill(1800);
    }
  }
}

string disc(const double value) {
  size_t idx = _axis.index(value);
  if (0 < idx && idx <= _axis.numBins()) return _edges[idx - 1];
  return "OTHER"s;
}


/// Normalise histograms etc., after the run
void finalize() {
  // normalisation factor
  const double br = 0.05961;
  const double factor = br * crossSection() / nanobarn / sumOfWeights();
  scale(_h_psi, factor);
  for (unsigned int ix = 0; ix < 3; ++ix) {
    for (auto& b : _h_psi[ix]->bins()) b.scaleW(1. / _axis.width(b.index()));
  }
  BinnedEstimatePtr<int> tmp;
  book(tmp, 1, 1, 1);
  efficiency(_h_total[0], _h_total[1], tmp);
}

/// @}


/// @name Histograms
/// @{
BinnedHistoPtr<int> _h_total[2];
BinnedHistoPtr<string> _h_psi[3];
YODA::Axis<double> _axis;
vector<string> _edges;
/// @}

};

RIVET_DECLARE_PLUGIN(CDF_1997_I440446);

} ```