Rivet analyses

Underlying event in leading jet events, extended to LHC

Experiment: ()

Status: VALIDATED

Authors: - Andy Buckley

References: none listed

Beams: * *

Beam energies: ANY

Run details: - LHC pp QCD interactions at 0.9, 10 or 14 TeV. Particles with cτ > 10 mm should be set stable. Several p⟂min cutoffs are probably required to fill the profile histograms.

Rick Field’s measurement of the underlying event in leading jet events, extended to the LHC. As usual, the leading jet of the defines an azimuthal toward/transverse/away decomposition, in this case the event is accepted within |η| < 2, as in the CDF 2008 version of the analysis. Since this isn’t the Tevatron, I’ve chosen to use k⟂ rather than midpoint jets.

Source code:MC_LEADJETUE.cc

// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/FinalState.hh"
#include "Rivet/Projections/ChargedFinalState.hh"
#include "Rivet/Projections/FastJets.hh"

namespace Rivet {


  /// @brief MC validation analysis for underlying event in jet events
  /// @author Andy Buckley
  class MC_LEADJETUE : public Analysis {
  public:

    /// Constructor
    MC_LEADJETUE()
      : Analysis("MC_LEADJETUE")
    {    }


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

    // Book histograms
    void init() {
      // Final state for the jet finding
      const FinalState fsj((Cuts::etaIn(-4.0, 4.0)));
      declare(fsj, "FSJ");
      declare(FastJets(fsj, JetAlg::KT, 0.7), "Jets");

      // Charged final state for the distributions
      const ChargedFinalState cfs((Cuts::etaIn(-1.0, 1.0) && Cuts::pT >=  0.5*GeV));
      declare(cfs, "CFS");

      const double maxpt1 = 500.0;
      book(_hist_pnchg      ,"trans-nchg", 50, 0.0, maxpt1);
      book(_hist_pmaxnchg   ,"trans-maxnchg", 50, 0.0, maxpt1);
      book(_hist_pminnchg   ,"trans-minnchg", 50, 0.0, maxpt1);
      book(_hist_pcptsum    ,"trans-ptsum", 50, 0.0, maxpt1);
      book(_hist_pmaxcptsum ,"trans-maxptsum", 50, 0.0, maxpt1);
      book(_hist_pmincptsum ,"trans-minptsum", 50, 0.0, maxpt1);
      book(_hist_pcptave    ,"trans-ptavg", 50, 0.0, maxpt1);
    }


    // Do the analysis
    void analyze(const Event& e) {

      const FinalState& fsj = apply<FinalState>(e, "FSJ");
      if (fsj.particles().empty()) {
        MSG_DEBUG("Failed multiplicity cut");
        vetoEvent;
      }

      const FastJets& jetpro = apply<FastJets>(e, "Jets");
      const Jets jets = jetpro.jetsByPt();
      MSG_DEBUG("Jet multiplicity = " << jets.size());

      // Require the leading jet to be within |eta| < 2
      if (jets.size() < 1 || fabs(jets[0].eta()) > 2) {
        MSG_DEBUG("Failed jet cut");
        vetoEvent;
      }

      const double jetphi = jets[0].phi();
      const double jetpT  = jets[0].pT();
      MSG_DEBUG("Leading jet: pT = " << jetpT/GeV << " GeV"
                << ", eta = " << jets[0].eta()
                << ", phi = " << jetphi);

      // Get the final states to work with for filling the distributions
      const FinalState& cfs = apply<ChargedFinalState>(e, "CFS");

      //size_t numOverall(0), numToward(0), numAway(0);
      size_t numTrans1(0), numTrans2(0);
      double ptSumTrans1(0.0), ptSumTrans2(0.0);
      double ptMaxOverall(0.0), ptMaxToward(0.0), ptMaxTrans1(0.0), ptMaxTrans2(0.0), ptMaxAway(0.0);

      // Calculate all the charged stuff
      for (const Particle& p : cfs.particles()) {
        const double dPhi = deltaPhi(p.phi(), jetphi);
        const double pT = p.pT();
        const double phi = p.phi();
        const double rotatedphi = phi - jetphi;

        //ptSumOverall += pT;
        //++numOverall;
        if (pT > ptMaxOverall) ptMaxOverall = pT;

        if (dPhi < PI/3.0) {
          //ptSumToward += pT;
          //++numToward;
          if (pT > ptMaxToward) ptMaxToward = pT;
        }
        else if (dPhi < 2*PI/3.0) {
          if (rotatedphi <= PI) {
            ptSumTrans1 += pT;
            ++numTrans1;
            if (pT > ptMaxTrans1) ptMaxTrans1 = pT;
          } else {
            ptSumTrans2 += pT;
            ++numTrans2;
            if (pT > ptMaxTrans2) ptMaxTrans2 = pT;
          }
        }
        else {
          //ptSumAway += pT;
          //++numAway;
          if (pT > ptMaxAway) ptMaxAway = pT;
        }
      }


      // Fill the histograms
      //_hist_tnchg->fill(jetpT/GeV, numToward/(4*PI/3));
      _hist_pnchg->fill(jetpT/GeV, (numTrans1+numTrans2)/(4*PI/3));
      _hist_pmaxnchg->fill(jetpT/GeV, (numTrans1>numTrans2 ? numTrans1 : numTrans2)/(2*PI/3));
      _hist_pminnchg->fill(jetpT/GeV, (numTrans1<numTrans2 ? numTrans1 : numTrans2)/(2*PI/3));
      //_hist_pdifnchg->fill(jetpT/GeV, abs(numTrans1-numTrans2)/(2*PI/3));
      //_hist_anchg->fill(jetpT/GeV, numAway/(4*PI/3));

      //_hist_tcptsum->fill(jetpT/GeV, ptSumToward/GeV/(4*PI/3));
      _hist_pcptsum->fill(jetpT/GeV, (ptSumTrans1+ptSumTrans2)/GeV/(4*PI/3));
      _hist_pmaxcptsum->fill(jetpT/GeV, (ptSumTrans1>ptSumTrans2 ? ptSumTrans1 : ptSumTrans2)/GeV/(2*PI/3));
      _hist_pmincptsum->fill(jetpT/GeV, (ptSumTrans1<ptSumTrans2 ? ptSumTrans1 : ptSumTrans2)/GeV/(2*PI/3));
      //_hist_pdifcptsum->fill(jetpT/GeV, fabs(ptSumTrans1-ptSumTrans2)/GeV/(2*PI/3));
      //_hist_acptsum->fill(jetpT/GeV, ptSumAway/GeV/(4*PI/3));

      //if (numToward > 0) {
      //  _hist_tcptave->fill(jetpT/GeV, ptSumToward/GeV/numToward);
      //  _hist_tcptmax->fill(jetpT/GeV, ptMaxToward/GeV);
      //}
      if ((numTrans1+numTrans2) > 0) {
        _hist_pcptave->fill(jetpT/GeV, (ptSumTrans1+ptSumTrans2)/GeV/(numTrans1+numTrans2));
        //_hist_pcptmax->fill(jetpT/GeV, (ptMaxTrans1 > ptMaxTrans2 ? ptMaxTrans1 : ptMaxTrans2)/GeV);
      }
      //if (numAway > 0) {
      //  _hist_acptave->fill(jetpT/GeV, ptSumAway/GeV/numAway);
      //  _hist_acptmax->fill(jetpT/GeV, ptMaxAway/GeV);
      //}
    }


    void finalize() {
      //
    }


  private:

    Profile1DPtr _hist_pnchg;
    Profile1DPtr _hist_pmaxnchg;
    Profile1DPtr _hist_pminnchg;
    Profile1DPtr _hist_pcptsum;
    Profile1DPtr _hist_pmaxcptsum;
    Profile1DPtr _hist_pmincptsum;
    Profile1DPtr _hist_pcptave;

  };



  RIVET_DECLARE_PLUGIN(MC_LEADJETUE);

}