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ATLAS_2016_I1467230

Track-based minimum bias with low-pT tracks at 13 TeV
Experiment: ATLAS (LHC)
Spires ID: 1467230
Status: VALIDATED
Authors:
  • Roman Lysak
References: Beams: p+ p+
Beam energies: (6500.0, 6500.0) GeV
Run details:
  • $pp$ QCD interactions at 13 TeV. Diffractive events should be included. Multiple kinematic cuts should not be required.

Measurements of distributions of charged particles produced in proton-proton collisions with a centre-of-mass energy of 13 TeV are presented. The data were recorded by the ATLAS detector at the LHC and correspond to an integrated luminosity of 151 $\mu$b$^{-1}$. The particles are required to have a transverse momentum greater than 100 MeV and an absolute pseudorapidity less than 2.5. The charged-particle multiplicity, its dependence on transverse momentum and pseudorapidity and the dependence of the mean transverse momentum on multiplicity are measured in events containing at least two charged particles satisfying the above kinematic criteria. The results are corrected for detector effects and compared to the predictions from several Monte Carlo event generators.

Source code: ATLAS_2016_I1467230.cc
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// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/ChargedFinalState.hh"

namespace Rivet {


  /// @brief ATLAS 13 TeV minimum bias analysis for low-pT tracks
  class ATLAS_2016_I1467230 : public Analysis {
  public:

    /// Particle types included
    enum PartTypes {
      k_NoStrange,
      k_AllCharged,
      kNPartTypes
    };

    /// Phase space regions
    enum regionID {
      k_pt100_nch2_eta25,
      kNregions
    };


    /// Default constructor
    DEFAULT_RIVET_ANALYSIS_CTOR(ATLAS_2016_I1467230);


    /// Initialization, called once before running
    void init() {

      for (int iT = 0; iT < kNPartTypes; ++iT) {
        for (int iR = 0; iR < kNregions; ++iR) {
          _sumW[iT][iR] = 0.;
        }
      }

      // Initialize and register projections
      declare(ChargedFinalState(Cuts::abseta < 2.5 && Cuts::pT > 100*MeV), "CFS100_25");

      for (int iT = 0; iT < kNPartTypes; ++iT) {
        for (int iR = 0; iR < kNregions; ++iR) {
          _hist_nch  [iT][iR] = bookHisto1D  ( 1, iR + 1, iT + 1);
          _hist_pt   [iT][iR] = bookHisto1D  ( 2, iR + 1, iT + 1);
          _hist_eta  [iT][iR] = bookHisto1D  ( 3, iR + 1, iT + 1);
          _hist_ptnch[iT][iR] = bookProfile1D( 4, iR + 1, iT + 1);
        }
      }

    }


    /// Fill histograms for the given particle selection and phase-space region
    void fillPtEtaNch(const Particles& particles, int ptype, int iRegion, double weight) {

      // Skip if event fails multiplicity cut
      const size_t nch = particles.size();
      if (nch < 2) return;

      // Fill event weight info
      _sumW[ptype][iRegion] += weight;

      // Fill nch
      _hist_nch[ptype][iRegion]->fill(nch, weight);

      // Loop over particles, fill pT, eta and ptnch
      for (const Particle& p : particles)  {
        const double pt  = p.pT()/GeV;
        const double eta = p.eta();
        _hist_pt   [ptype][iRegion]->fill(pt , weight/pt);
        _hist_eta  [ptype][iRegion]->fill(eta, weight);
        _hist_ptnch[ptype][iRegion]->fill(nch, pt, weight);
      }
    }


    /// Per-event analysis
    void analyze(const Event& event) {

      // Get all charged particles
      const ChargedFinalState& cfs = apply<ChargedFinalState>(event, "CFS100_25");
      const Particles& pall = cfs.particles();

      // Get charged particles, filtered to omit charged strange baryons
      const Cut& pcut = Cuts::abspid != PID::SIGMAMINUS && Cuts::abspid != PID::SIGMAPLUS && Cuts::abspid != PID::XIMINUS && Cuts::abspid != PID::OMEGAMINUS;
      const Particles& pnostrange = cfs.particles(pcut);

      // Fill all histograms
      for (int iR = 0; iR < kNregions; ++iR)  {
        fillPtEtaNch(pall,       k_AllCharged, iR, event.weight());
        fillPtEtaNch(pnostrange, k_NoStrange,  iR, event.weight());
      }

    }


    /// Post-run data manipulation
    void finalize() {

      // Scale all histograms
      for (int iT = 0; iT < kNPartTypes; ++iT) {
        for (int iR = 0; iR < kNregions; ++iR) {
          if (_sumW[iT][iR] > 0) {
            scale(_hist_nch[iT][iR], 1.0/_sumW[iT][iR]);
            scale(_hist_pt [iT][iR], 1.0/_sumW[iT][iR]/TWOPI/5.);
            scale(_hist_eta[iT][iR], 1.0/_sumW[iT][iR]);
          }
        }
      }

    }


  private:

    /// Weight sums
    double _sumW[kNPartTypes][kNregions];

    /// @name Histogram arrays
    //@{
    Histo1DPtr   _hist_nch    [kNPartTypes][kNregions];
    Histo1DPtr   _hist_pt     [kNPartTypes][kNregions];
    Histo1DPtr   _hist_eta    [kNPartTypes][kNregions];
    Profile1DPtr _hist_ptnch  [kNPartTypes][kNregions];
    //@}

  };


  // The hook for the plugin system
  DECLARE_RIVET_PLUGIN(ATLAS_2016_I1467230);

}