Rivet analyses

title: LHCB_2012_I1087907

Relative rates of prompt $\chi_{c2}$/$\chi_{c1}$ production at 7 TeV

Experiment: LHCB (LHC)

Inspire ID: 1087907

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 $\chi_{c2}$/$\chi_{c1}$ production at 7 TeV using the decay to $J/\psi\gamma$ by the LHCb collaboration.

Source code:LHCB_2012_I1087907.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief chi_c at 7 TeV class LHCB_2012_I1087907 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(LHCB_2012_I1087907);


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

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


/// Perform the per-event analysis
void analyze(const Event& event) {

  // Final state of unstable particles to get particle spectra
  const UnstableParticles& ufs = apply<UnstableParticles>(event, "UFS");

  for (const Particle& p : ufs.particles(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 = p.pid() == 20443 ? 0 : 1;
    double xp = Jpsi.perp();
    _h_chi[ichi]->fill(xp);
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  // chi_c to gamma J/psi branching ratios from PDG 2021
  vector<double> br = {0.343, 0.190};
  Estimate1DPtr tmp;
  book(tmp, 1, 1, 1);
  divide(_h_chi[1], _h_chi[0], tmp);
  tmp->scale(br[1] / br[0]);
}

/// @}


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

};

RIVET_DECLARE_PLUGIN(LHCB_2012_I1087907);

} ```