Rivet analyses

μ+μ− production in ultraperipheral Pb+Pb collisions at $\sqrt{s}_{NN}=5.02$TeV

Experiment: ATLAS (LHC)

Inspire ID: 1832628

Status: VALIDATED

Authors: - Peter Richardson

References: - Phys.Rev.C 104 (2021) 024906, 2021 - arXiv: 2011.12211 - Expt page: ATLAS-HION-2016-02

Beams: 1000822080 1000822080

Beam energies: (522080.0, 522080.0)GeV

Run details: - ultraperipheral Pb+Pb collisions producing mu+mu- mmainly via gamma gamma

Measurement of a number of double-differential distributions in ${\rm Pb}{\rm Pb}(\gamma\gamma)\to \mu^+\mu^-({\rm Pb}^{(*)}{\rm Pb}^{(*)})$

Source code:ATLAS_2021_I1832628.cc

// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/ChargedFinalState.hh"
#include "Rivet/Projections/IdentifiedFinalState.hh"

namespace Rivet {


  /// @brief gamma gamma -> mu+ mu-
  class ATLAS_2021_I1832628 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(ATLAS_2021_I1832628);


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

    /// Book histograms and initialise projections before the run
    void init() {
      // projections
      ChargedFinalState cfs(Cuts::abseta < 2.4 and Cuts::pT > 100 * MeV);
      declare(cfs, "CFS");
      // Get muons which pass the initial kinematic cuts
      IdentifiedFinalState muon_fs(Cuts::abseta < 2.4 && Cuts::pT > 4 * GeV);
      muon_fs.acceptIdPair(PID::MUON);
      declare(muon_fs, "MUON_FS");
      // histograms
      vector<double> mbins = {10, 20, 40, 80}, ybins = {0., 0.8, 1.6, 2.4};
      book(_d_y_m, mbins);
      for (auto& b : _d_y_m->bins()) book(b, b.index(), 1, 1);
      book(_d_m_y, ybins);
      for (auto& b : _d_m_y->bins()) book(b, b.index() + 6, 1, 1);
      book(_d_cTheta_dm[0], mbins);
      for (auto& b : _d_cTheta_dm[0]->bins()) book(b, b.index() + 12, 1, 1);
      book(_d_cTheta_dm[1], mbins);
      for (auto& b : _d_cTheta_dm[1]->bins()) book(b, b.index() + 18, 1, 1);
      book(_h_aco, 29, 1, 1);
    }


    /// Perform the per-event analysis
    void analyze(const Event& event) {
      const ChargedFinalState& cfs = apply<ChargedFinalState>(event, "CFS");
      if (cfs.size() != 2) vetoEvent; // no other charged particles in 2.5
      // extract the muons
      const Particles& muonFS = apply<IdentifiedFinalState>(event, "MUON_FS").particles();
      // have 2 muons with opposite charge
      if (muonFS.size() != 2) vetoEvent;
      if (muonFS[0].pid() != -muonFS[1].pid()) vetoEvent;
      // mu+mu- pair invariant mass
      FourMomentum pmumu = muonFS[0].momentum() + muonFS[1].momentum();
      const double mmumu = pmumu.mass();
      if (mmumu < 10. * GeV) vetoEvent;
      // mu+mu- pT
      const double pTmumu = pmumu.perp();
      if (pTmumu > 2.) vetoEvent;
      double ymumu = abs(pmumu.rapidity());
      _d_y_m->fill(mmumu, ymumu);
      _d_m_y->fill(ymumu, mmumu);
      double yp = muonFS[0].rapidity();
      double ym = muonFS[1].rapidity();
      double cTheta = abs(tanh(0.5 * (yp - ym)));
      _d_cTheta_dm[0]->fill(mmumu, cTheta);
      if (ymumu < 0.8) _d_cTheta_dm[1]->fill(mmumu, cTheta);
      double aco = 1. - deltaPhi(muonFS[0], muonFS[1]) / M_PI;
      _h_aco->fill(aco);
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      scale(_d_y_m, crossSection() / microbarn / sumOfWeights());
      scale(_d_m_y, crossSection() / microbarn / sumOfWeights());
      scale(_d_cTheta_dm, crossSection() / microbarn / sumOfWeights());
      scale(_h_aco, crossSection() / microbarn / sumOfWeights());
    }

    /// @}


    /// @name Histograms
    /// @{
    Histo1DGroupPtr _d_y_m, _d_m_y, _d_cTheta_dm[2];
    Histo1DPtr _h_aco;
    /// @}
  };


  RIVET_DECLARE_PLUGIN(ATLAS_2021_I1832628);

}