Rivet analyses

Relative rates of prompt χc2/χc1 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 χc2/χc1 production at 7 TeV using the decay to J/ψγ by the LHCb collaboration.

Source code:LHCB_2012_I1087907.cc

// -*- 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);

}