Rivet analyses

title: LHCB_2013_I1242869

Relative rates of prompt $\chi_{c(0,1,2)}$ production at 7 TeV

Experiment: LHCB (LHC)

Inspire ID: 1242869

Status: VALIDATED

Authors: - Peter Richardson

References: - JHEP 10 (2013) 115

Beams: p+ p+

Beam energies: (3500.0, 3500.0)GeV

Run details: - chi_c(0,1,2) production

Measurement of the relative rates of prompt $\chi_{c(0,1,2)}$ production at 7 TeV using the decay to $J/\psi\gamma$ by the LHCb collaboration.

Source code:LHCB_2013_I1242869.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief chi_c at 7 TeV class LHCB_2013_I1242869 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(LHCB_2013_I1242869);


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

/// Book histograms and initialise projections before the run
void init() {
  declare(UnstableParticles(), "UFS");
  for (unsigned int ichi = 0; ichi < 3; ++ichi) {
    book(_h_chi[ichi], "TMP/h_CHI_" + toString(ichi), refData(1, 1, 1));
    book(_c_chi[ichi], "TMP/c_CHI_" + toString(ichi));
  }
  book(_r, 2, 1, 1);
}


/// Perform the per-event analysis
void analyze(const Event& event) {
  if (_edges.empty()) _edges = _r->xEdges();
  // Final state of unstable particles to get particle spectra
  const UnstableParticles& ufs = apply<UnstableParticles>(event, "UFS");

  for (const Particle& p : ufs.particles(Cuts::pid == 10441 || Cuts::pid == 20443 || Cuts::pid == 445)) {
    // prompt
    if (p.fromBottom()) continue;
    // J/psi /gamma mode
    if (p.children().size() != 2) continue;
    Particle Jpsi;
    if (p.children()[0].pid() == 22 && p.children()[1].pid() == 443) {
      Jpsi = p.children()[1];
    }
    else if (p.children()[1].pid() == 22 && p.children()[0].pid() == 443) {
      Jpsi = p.children()[0];
    }
    else
      continue;
    double absrap = Jpsi.absrap();
    if (absrap < 2. || absrap > 4.5) continue;
    unsigned int ichi = 0;
    if (p.pid() == 20443)
      ichi = 1;
    else if (p.pid() == 445)
      ichi = 2;
    double xp = Jpsi.perp();
    _h_chi[ichi]->fill(xp);
    if (xp > 4. && xp < 20.) {
      _c_chi[ichi]->fill();
      if (ichi == 0)
        _r->fill(_edges[0]);
      else if (ichi == 2)
        _r->fill(_edges[1]);
    }
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  // chi_c to gamma J/psi branching ratios from PDG 2021
  vector<double> br = {0.014, 0.343, 0.190};
  // divide out the branching ratio for mode used to get total rate
  for (unsigned int ichi = 0; ichi < 3; ++ichi) {
    scale(_h_chi[ichi], 1. / br[ichi]);
    scale(_c_chi[ichi], 1. / br[ichi]);
  }
  // ratio chi_c2/chi_c2
  Estimate1DPtr tmp;
  book(tmp, 1, 1, 1);
  divide(_h_chi[2], _h_chi[1], tmp);
  _r->bin(1).scaleW(double(1. / br[0] / _c_chi[2]->val()));
  _r->bin(2).scaleW(1. / br[2] / _c_chi[1]->val());
}

/// @}


/// @name Histograms
/// @{
Histo1DPtr _h_chi[3];
BinnedHistoPtr<string> _r;
CounterPtr _c_chi[3];
vector<string> _edges;
/// @}

};

RIVET_DECLARE_PLUGIN(LHCB_2013_I1242869);

} ```