Rivet analyses

Relative rates of prompt χc(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 χc(0, 1, 2) production at 7 TeV using the decay to J/ψγ by the LHCb collaboration.

Source code:LHCB_2013_I1242869.cc

// -*- 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);

}