Rivet analyses

title: 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

```c++ // -- C++ --

include "Rivet/Analysis.hh"

include "Rivet/Projections/ChargedFinalState.hh"

include "Rivet/Projections/IdentifiedFinalState.hh"

namespace Rivet {

/// @brief gamma gamma -> mu+ mu- class ATLAS_2018_I1615866 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(ATLAS_2018_I1615866);


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

/// Book histograms and initialise projections before the run
void init() {
  ChargedFinalState cfs(Cuts::abseta < 2.5 and Cuts::pT > 0.4);
  declare(cfs, "CFS");
  // Get muons which pass the initial kinematic cuts
  IdentifiedFinalState muon_fs(Cuts::abseta < 2.4 && Cuts::pT > 6 * GeV);
  muon_fs.acceptIdPair(PID::MUON);
  declare(muon_fs, "MUON_FS");
  // histograms
  book(_h_sigma, 1, 1, 1);
  book(_h_mass, 2, 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;
  // invariant mass between 12 and 70
  const double mmumu = (muonFS[0].momentum() + muonFS[1].momentum()).mass();
  if (mmumu < 12. or mmumu > 70.) vetoEvent;
  // cut pt >10 if pair mass >30
  for (unsigned int ix = 0; ix < 2; ++ix) {
    if (mmumu > 30 && muonFS[ix].perp() < 10.) vetoEvent;
  }
  // fill histogram
  _h_mass->fill(mmumu);
  _h_sigma->fill();
}


/// Normalise histograms etc., after the run
void finalize() {
  scale(_h_sigma, crossSection() / picobarn / sumOfWeights());
  scale(_h_mass, crossSection() / picobarn / sumOfWeights());
}

/// @}


/// @name Histograms
/// @{
CounterPtr _h_sigma;
Histo1DPtr _h_mass;
/// @}

};

RIVET_DECLARE_PLUGIN(ATLAS_2018_I1615866);

} ```