Rivet analyses

Forward Z boson production cross-section in proton-proton collisions at $\sqrt{s}=13$ TeV

Experiment: LHCB (LHC)

Inspire ID: 1990313

Status: VALIDATED

Authors: - Hang Yin

References: - JHEP 07 (2022) 026 - DOI:10.1007/JHEP07(2022)026 - arXiv: 2112.07458

Beams: p+ p+

Beam energies: (6500.0, 6500.0)GeV

Run details: - Proton-proton collisions at $\sqrt{s}=13$ TeV, measurement of the Z boson production cross section in the forward region. The production cross-section is measured using the Z → μ+μ− events in the fiducial region, defined as pseudorapidity 2.0 < η < 4.5 and pT > 20 GeV/c for both constituent muons, and dimuon invariant mass 60 < Mμμ < 120 GeV/c2.

A precision measurement of the Z0 boson production cross-section at $\sqrt{s} = 13$ TeV in the forward region is presented, using pp collision data collected by the LHCb detector, corresponding to an integrated luminosity of 5.1 fb−1. The production cross-section is measured using Z → μ+μ− events within the fiducial region defined as pseudorapidity 2.0 < η < 4.5 and transverse momentum pT > 20 GeV/c for both muons and dimuon invariant mass 60 < Mμμ < 120 GeV/c2. The integrated cross-section is determined to be where the first uncertainty is statistical, the second is systematic, and the third is due to the luminosity determination. The measured results are in agreement with theoretical predictions within uncertainties.

Source code:LHCB_2021_I1990313.cc

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

namespace Rivet {


  /// @brief Forward Z production cross-section in pp collisions at 13 TeV
  class LHCB_2021_I1990313 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(LHCB_2021_I1990313);


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

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

      // Initialise and register projections
      DileptonFinder zmumufinder(91.2*GeV, 0.1, Cuts::absetaIn(2.0, 4.5) && Cuts::pT > 20 * GeV &&
                                 Cuts::abspid == PID::MUON, Cuts::massIn(60*GeV, 120*GeV));
      declare(zmumufinder, "ZmumuFinder");

      // Book histograms
      // specify custom binning
      book(_h_sigma_vs_y,    18, 1, 1);
      book(_h_sigma_vs_pt,   19, 1, 1);
      book(_h_sigma_vs_phi,  20, 1, 1);
      book(_h_sigma_vs_ypt,  {2., 2.5, 3., 3.5, 4., 4.5});
      book(_h_sigma_vs_yphi, {2., 2.5, 3., 3.5, 4., 4.5});
      for (size_t i = 1; i < _h_sigma_vs_ypt->numBins()+1; ++i) {
        book(_h_sigma_vs_ypt->bin(i),  21, 1, i);
        book(_h_sigma_vs_yphi->bin(i), 22, 1, i);
      }
    }


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

      // Retrieve dressed leptons, sorted by pT
      const DileptonFinder& zmumufinder = apply<DileptonFinder>(event, "ZmumuFinder");
      if(zmumufinder.empty()) vetoEvent;
      if(zmumufinder.bosons().size() > 1)
        MSG_WARNING("Found multiple (" << zmumufinder.bosons().size() << ") Z -> mu+ mu- decays!");

      // Z momenta
      FourMomentum zmumu = zmumufinder.bosons()[0].momentum();
      if (zmumufinder.leptons().size() < 2) vetoEvent;

      const Particle& muon_p = zmumufinder.constituents()[0];
      const Particle& muon_m = zmumufinder.constituents()[1];

      const double diffphi = deltaPhi(muon_p, muon_m);
      const double diffpsd = deltaEta(muon_p, muon_m);
      const double accphi = M_PI - diffphi;
      const double angular = tan(accphi/2) / cosh(diffpsd/2);

      _h_sigma_vs_y->fill(zmumu.absrapidity());
      _h_sigma_vs_pt->fill(zmumu.pT()/GeV);
      _h_sigma_vs_phi->fill(angular);
      _h_sigma_vs_ypt->fill(zmumu.absrapidity(), zmumu.pT()/GeV);
      _h_sigma_vs_yphi->fill(zmumu.absrapidity(), angular);
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      const double xs = crossSection()/picobarn;
      double scale_f = xs/sumOfWeights()/2.;
      _h_sigma_vs_y->scaleW(scale_f);
      _h_sigma_vs_pt->scaleW(scale_f);
      _h_sigma_vs_phi->scaleW(scale_f);
      scale(_h_sigma_vs_ypt,  scale_f*2.);
      scale(_h_sigma_vs_yphi, scale_f*2.);
    }

    ///@}


    Histo1DPtr _h_sigma_vs_y, _h_sigma_vs_pt, _h_sigma_vs_phi;
    Histo1DGroupPtr _h_sigma_vs_ypt, _h_sigma_vs_yphi;

  };


  RIVET_DECLARE_PLUGIN(LHCB_2021_I1990313);

}