Rivet analyses

title: CMS_2012_PAS_FSQ_12_020

Studies of the underlying event at 7 TeV with leading charged particles

Experiment: CMS (LHC)

Inspire ID: 1407839

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

```c++ // -- 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
RIVET_DEFAULT_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 = apply<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
  _NchgPMXden1->fill(ptlead / GeV, NchgPmax / AREA);
  _NchgPMNden1->fill(ptlead / GeV, NchgPmin / AREA);
  _NchgPDFden1->fill(ptlead / GeV, NchgPDFden);
  _PTsumPMXden1->fill(ptlead / GeV, PTsumPmax / AREA);
  _PTsumPMNden1->fill(ptlead / GeV, PTsumPmin / AREA);
  _PTsumPDFden1->fill(ptlead / GeV, PTsumPDFden);
}


/// 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;

};

RIVET_DECLARE_PLUGIN(CMS_2012_PAS_FSQ_12_020);

} ```