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ATLAS_2018_I1615866

Exclusive photon-photon production of muon pairs in proton-proton collisions at $\sqrt{s} = 13$ TeV
Experiment: ATLAS (LHC)
Inspire ID: 1615866
Status: VALIDATED
Authors:
  • Peter Richardson
References:
  • Phys.Lett.B 777 (2018) 303-323
Beams: p+ p+
Beam energies: (6500.0, 6500.0) GeV
Run details:
  • gamma gamma -> mu+ mu- process.

The production of exclusive $\gamma\gamma\to\mu^+\mu^-$ events in proton-proton collisions at a centre-of-mass energy of 13 TeV is measured with the ATLAS detector at the LHC, using data corresponding to an integrated luminosity of $3.2 \text{fb}^{-1}$. The measurement is performed for a dimuon invariant mass of between 12 GeV and 70 GeV, including the differential cross section as a function of the mass.

Source code: ATLAS_2018_I1615866.cc
 1// -*- C++ -*-
 2#include "Rivet/Analysis.hh"
 3#include "Rivet/Projections/ChargedFinalState.hh"
 4#include "Rivet/Projections/IdentifiedFinalState.hh"
 5
 6namespace Rivet {
 7
 8
 9  /// @brief gamma gamma -> mu+ mu-
10  class ATLAS_2018_I1615866 : public Analysis {
11  public:
12
13    /// Constructor
14    RIVET_DEFAULT_ANALYSIS_CTOR(ATLAS_2018_I1615866);
15
16
17    /// @name Analysis methods
18    /// @{
19
20    /// Book histograms and initialise projections before the run
21    void init() {
22      ChargedFinalState cfs(Cuts::abseta < 2.5 and Cuts::pT>0.4);
23      declare(cfs,"CFS");
24      // Get muons which pass the initial kinematic cuts
25      IdentifiedFinalState muon_fs(Cuts::abseta < 2.4 && Cuts::pT > 6*GeV);
26      muon_fs.acceptIdPair(PID::MUON);
27      declare(muon_fs, "MUON_FS");
28      // histograms
29      book(_h_sigma,1,1,1);
30      book(_h_mass ,2,1,1);
31    }
32
33    /// Perform the per-event analysis
34    void analyze(const Event& event) {
35      const ChargedFinalState& cfs = apply<ChargedFinalState>(event, "CFS");
36      if (cfs.size() != 2) vetoEvent; // no other charged particles in 2.5
37      // extract the muons
38      const Particles& muonFS = apply<IdentifiedFinalState>(event, "MUON_FS").particles();
39      // have 2 muons with opposite charge
40      if (muonFS.size() != 2) vetoEvent;
41      if (muonFS[0].pid() != -muonFS[1].pid()) vetoEvent;
42      // invariant mass between 12 and 70
43      const double mmumu = (muonFS[0].momentum()+muonFS[1].momentum()).mass();
44      if(mmumu<12. or mmumu>70.)  vetoEvent;
45      // cut pt >10 if pair mass >30
46      for(unsigned int ix=0;ix<2;++ix) {
47        if(mmumu>30 && muonFS[ix].perp()<10.)  vetoEvent;
48      }
49      // fill histogram
50      _h_mass->fill(mmumu);
51      _h_sigma->fill();
52    }
53
54
55    /// Normalise histograms etc., after the run
56    void finalize() {
57      scale(_h_sigma, crossSection()/picobarn/sumOfWeights());
58      scale(_h_mass , crossSection()/picobarn/sumOfWeights());
59    }
60
61    /// @}
62
63
64    /// @name Histograms
65    /// @{
66    CounterPtr _h_sigma;
67    Histo1DPtr _h_mass;
68    /// @}
69
70
71  };
72
73
74  RIVET_DECLARE_PLUGIN(ATLAS_2018_I1615866);
75
76}