Rivet analyses

Relative rate of χc1 to χc2 production at 7 TeV

Experiment: CMS (LHC)

Inspire ID: 1189050

Status: VALIDATED

Authors: - Peter Richardson

References: - Eur.Phys.J.C 72 (2012) 2251, 2012. - arXiv: 1210.0875 - Expt page: CMS-BPH-11-010

Beams: p+ p+

Beam energies: (3500.0, 3500.0)GeV

Run details: - chi_c(1,2) production

Measurement of the relative rates of prompt χc1 to χc2 production at 7 TeV using the decay to J/ψγ by the CMS collaboration.

Source code:CMS_2012_I1189050.cc

// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {


  /// @brief chi_c at 7 TeV
  class CMS_2012_I1189050 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(CMS_2012_I1189050);


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

    /// Book histograms and initialise projections before the run
    void init() {
      declare(UnstableParticles(), "UFS");
      for(unsigned int ichi=0; ichi<2; ++ichi) {
        for (unsigned int ipT=0; ipT<2; ++ipT) {
          book(_h_chi[ichi][ipT], "TMP/h_CHI_"+toString(ichi)+"_"+toString(ipT), 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,gamma;
        if (p.children()[0].pid()==22 && p.children()[1].pid()==443) {
          Jpsi  = p.children()[1];
          gamma = p.children()[0];
        }
        else if (p.children()[1].pid()==22 && p.children()[0].pid()==443) {
          Jpsi  = p.children()[0];
          gamma = p.children()[1];
        }
        else {
          continue;
        }
        if (Jpsi.absrap()>1.) continue;
        const double xp=Jpsi.perp();
        unsigned int ichi = p.pid()==20443 ? 0 : 1;
        if (gamma.perp()>0.5) {
          _h_chi[ichi][0]->fill(xp);
        }
        _h_chi[ichi][1]->fill(xp);
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      // chi_c to gamma J/psi branching ratios from PDG 2021
      const vector<double> br = {0.343,0.190};
      // no br correction fiduical region
      Estimate1DPtr tmp;
      book(tmp, 1, 1, 1);
      divide(_h_chi[1][0], _h_chi[0][0], tmp);
      // br correction fiduical region
      book(tmp, 2, 1, 1);
      divide(_h_chi[1][0], _h_chi[0][0], tmp);
      tmp->scale(br[0]/br[1]);
      // no br correction  pT gamma >0
      book(tmp, 3, 1, 1);
      divide(_h_chi[1][1], _h_chi[0][1], tmp);
    }

    /// @}


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


  };


  RIVET_DECLARE_PLUGIN(CMS_2012_I1189050);

}