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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
  1// -*- C++ -*-
  2#include "Rivet/Analysis.hh"
  3#include "Rivet/Projections/ChargedFinalState.hh"
  4
  5namespace Rivet {
  6
  7
  8  /// @brief CMS underlying event in leading track events at 7 TeV
  9  /// @author Paolo Gunnellini (DESY)
 10  ///
 11  /// CMS measurement of the underlying event in "leading track" events.
 12  class CMS_2012_PAS_FSQ_12_020 : public Analysis {
 13  public:
 14
 15    /// Constructor
 16    RIVET_DEFAULT_ANALYSIS_CTOR(CMS_2012_PAS_FSQ_12_020);
 17
 18
 19    /// Book histograms and initialise projections before the run
 20    void init() {
 21
 22      const ChargedFinalState cfs(Cuts::abseta < 0.8 && Cuts::pT > 0.5*GeV);
 23      declare(cfs, "Tracks");
 24
 25      book(_NchgPDFden1 ,7,1,1);
 26      book(_NchgPMNden1 ,6,1,1);
 27      book(_NchgPMXden1 ,5,1,1);
 28      book(_PTsumPDFden1,10,1,1);
 29      book(_PTsumPMNden1,9,1,1);
 30      book(_PTsumPMXden1,8,1,1);
 31    }
 32
 33
 34    /// Perform the per-event analysis
 35    void analyze(const Event& event) {
 36
 37
 38      // Require at least one track in the event with pT >= 0.5 GeV
 39      const FinalState& cfs = applyProjection<ChargedFinalState>(event, "Tracks");
 40      if (cfs.empty()) vetoEvent;
 41      const Particles trks = cfs.particlesByPt();
 42
 43      // Identify leading track and its phi and pT
 44      const Particle p_lead = trks[0];
 45      const double philead = p_lead.momentum().phi();
 46      const double ptlead  = p_lead.momentum().pT();
 47
 48      // Loop over particles and build transverse side variables
 49      double NchgP1 = 0, NchgP2 = 0, PTsumP1 = 0, PTsumP2 = 0;
 50      for (const Particle& p : trks) {
 51
 52        // Region definition -- if not in transverse region, ignore
 53        const double dphi = mapAngle0To2Pi(p.phi() - philead);
 54        if (!inRange(dphi, PI/3, 2*PI/3) && !inRange(dphi, 4*PI/3, 5*PI/3)) continue;
 55
 56        // Transverse region 1
 57        if (inRange(dphi, PI/3, 2*PI/3)) {
 58          NchgP1 += 1;
 59          PTsumP1 += p.pT();
 60        }
 61        // Transverse region 2
 62        else if (inRange(dphi, 4*PI/3, 5*PI/3)) {
 63          NchgP2 += 1;
 64          PTsumP2 += p.pT();
 65        }
 66      }
 67
 68      // Calculate total variables
 69      // const double NchgPtot = (NchgP1 + NchgP2)/2;
 70      const double NchgPmax = max(NchgP1,NchgP2);
 71      const double NchgPmin = min(NchgP1,NchgP2);
 72      // const double PTsumPtot = (PTsumP1 + PTsumP2)/2;
 73      const double PTsumPmax = max(PTsumP1,PTsumP2);
 74      const double PTsumPmin = min(PTsumP1,PTsumP2);
 75      //
 76      const double PTsumPMXden = PTsumPmax/AREA;
 77      const double PTsumPMNden = PTsumPmin/AREA;
 78      const double NchgPMXden = NchgPmax/AREA;
 79      const double NchgPMNden = NchgPmin/AREA;
 80      //
 81      const double NchgPDFden = NchgPMXden - NchgPMNden;
 82      const double PTsumPDFden = PTsumPMXden - PTsumPMNden;
 83
 84      // Fill histograms
 85      const double weight = 1.0;
 86      _NchgPMXden1->fill(ptlead/GeV, NchgPmax/AREA, weight);
 87      _NchgPMNden1->fill(ptlead/GeV, NchgPmin/AREA, weight);
 88      _NchgPDFden1->fill(ptlead/GeV, NchgPDFden, weight);
 89      _PTsumPMXden1->fill(ptlead/GeV, PTsumPmax/AREA, weight);
 90      _PTsumPMNden1->fill(ptlead/GeV, PTsumPmin/AREA, weight);
 91      _PTsumPDFden1->fill(ptlead/GeV, PTsumPDFden, weight);
 92
 93    }
 94
 95
 96    /// eta-phi area of the transverse region
 97    constexpr static double AREA = 2*0.8 * M_PI/3;
 98
 99    /// Histograms
100    Profile1DPtr _NchgPden1, _NchgPMXden1, _NchgPMNden1, _NchgPDFden1, _PTsumPden1, _PTsumPMXden1, _PTsumPMNden1, _PTsumPDFden1;
101
102  };
103
104
105  // The hook for the plugin system
106  RIVET_DECLARE_PLUGIN(CMS_2012_PAS_FSQ_12_020);
107
108}