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);

}