Rivet analyses

title: ATLAS_2021_I1832628

$\mu^+\mu^-$ 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++ // -- 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);

} ```