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CMS_2012_PAS_FSQ_12_020

Studies of the underlying event at 7 TeV with leading charged particles
Experiment: CMS (LHC)
Status: VALIDATED
Authors:
  • Hannes Jung
  • Paolo Gunnellini
References:
  • CERN-PH-EP-2015-291
Beams: p+ p+
Beam energies: (3500.0, 3500.0) GeV
Run details:
  • Minimum bias events at 7 TeV.

We study charged particle production in proton--proton collisions at 7 TeV. We use the direction of the charged particle with the largest transverse momentum in each event to define three regions of $\eta$--$\phi$ space: toward, away, and transverse. The average number and the average scalar pT sum of charged particles in the transverse region are sensitive to the modeling of the underlying event. The transverse region is divided into a MAX and MIN transverse region, which helps separate the hard component (initial and final-state radiation) from the beam--beam remnant and multiple parton interaction components of the scattering.

Source code: CMS_2012_PAS_FSQ_12_020.cc
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// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/ChargedFinalState.hh"

namespace Rivet {


  /// @brief CMS underlying event in leading track events at 7 TeV
  /// @author Paolo Gunnellini (DESY)
  ///
  /// CMS measurement of the underlying event in "leading track" events.
  class CMS_2012_PAS_FSQ_12_020 : public Analysis {
  public:

    /// Constructor
    DEFAULT_RIVET_ANALYSIS_CTOR(CMS_2012_PAS_FSQ_12_020);


    /// Book histograms and initialise projections before the run
    void init() {

      const ChargedFinalState cfs(Cuts::abseta < 0.8 && Cuts::pT > 0.5*GeV);
      declare(cfs, "Tracks");

      book(_NchgPDFden1 ,7,1,1);
      book(_NchgPMNden1 ,6,1,1);
      book(_NchgPMXden1 ,5,1,1);
      book(_PTsumPDFden1,10,1,1);
      book(_PTsumPMNden1,9,1,1);
      book(_PTsumPMXden1,8,1,1);
    }


    /// Perform the per-event analysis
    void analyze(const Event& event) {


      // Require at least one track in the event with pT >= 0.5 GeV
      const FinalState& cfs = applyProjection<ChargedFinalState>(event, "Tracks");
      if (cfs.empty()) vetoEvent;
      const Particles trks = cfs.particlesByPt();

      // Identify leading track and its phi and pT
      const Particle p_lead = trks[0];
      const double philead = p_lead.momentum().phi();
      const double ptlead  = p_lead.momentum().pT();

      // Loop over particles and build transverse side variables
      double NchgP1 = 0, NchgP2 = 0, PTsumP1 = 0, PTsumP2 = 0;
      for (const Particle& p : trks) {

        // Region definition -- if not in transverse region, ignore
        const double dphi = mapAngle0To2Pi(p.phi() - philead);
        if (!inRange(dphi, PI/3, 2*PI/3) && !inRange(dphi, 4*PI/3, 5*PI/3)) continue;

        // Transverse region 1
        if (inRange(dphi, PI/3, 2*PI/3)) {
          NchgP1 += 1;
          PTsumP1 += p.pT();
        }
        // Transverse region 2
        else if (inRange(dphi, 4*PI/3, 5*PI/3)) {
          NchgP2 += 1;
          PTsumP2 += p.pT();
        }
      }

      // Calculate total variables
      // const double NchgPtot = (NchgP1 + NchgP2)/2;
      const double NchgPmax = max(NchgP1,NchgP2);
      const double NchgPmin = min(NchgP1,NchgP2);
      // const double PTsumPtot = (PTsumP1 + PTsumP2)/2;
      const double PTsumPmax = max(PTsumP1,PTsumP2);
      const double PTsumPmin = min(PTsumP1,PTsumP2);
      //
      const double PTsumPMXden = PTsumPmax/AREA;
      const double PTsumPMNden = PTsumPmin/AREA;
      const double NchgPMXden = NchgPmax/AREA;
      const double NchgPMNden = NchgPmin/AREA;
      //
      const double NchgPDFden = NchgPMXden - NchgPMNden;
      const double PTsumPDFden = PTsumPMXden - PTsumPMNden;

      // Fill histograms
      const double weight = 1.0;
      _NchgPMXden1->fill(ptlead/GeV, NchgPmax/AREA, weight);
      _NchgPMNden1->fill(ptlead/GeV, NchgPmin/AREA, weight);
      _NchgPDFden1->fill(ptlead/GeV, NchgPDFden, weight);
      _PTsumPMXden1->fill(ptlead/GeV, PTsumPmax/AREA, weight);
      _PTsumPMNden1->fill(ptlead/GeV, PTsumPmin/AREA, weight);
      _PTsumPDFden1->fill(ptlead/GeV, PTsumPDFden, weight);

    }


    /// eta-phi area of the transverse region
    constexpr static double AREA = 2*0.8 * M_PI/3;

    /// Histograms
    Profile1DPtr _NchgPden1, _NchgPMXden1, _NchgPMNden1, _NchgPDFden1, _PTsumPden1, _PTsumPMXden1, _PTsumPMNden1, _PTsumPDFden1;

  };


  // The hook for the plugin system
  DECLARE_RIVET_PLUGIN(CMS_2012_PAS_FSQ_12_020);

}