Rivet analyses

title: ATLAS_2012_I1204784

Measurement of angular correlations in Drell-Yan lepton pairs to probe $Z/\gamma^*$ boson transverse momentum

Experiment: ATLAS (LHC)

Inspire ID: 1204784

Status: VALIDATED

Authors: - Elena Yatsenko - Kiran Joshi

References: - Expt page: ATLAS-STDM-2012-06 - arXiv: 1211.6899

Beams: p+ p+

Beam energies: (3500.0, 3500.0)GeV

Run details: - $Z/\gamma^*$ production with decays to electrons and/or muons.

A measurement of angular correlations in Drell-Yan lepton pairs via the $\phi^$ observable is presented. This variable probes the same physics as the $Z/\gamma^$ boson transverse momentum with a better experimental resolution. The $Z/\gamma^ \to ee$ and $Z/\gamma^ \to \mu \mu$ decays produced in proton--proton collisions at a centre-of-mass energy of $\sqrt{s} = 7~\TeV$ are used. Normalised differential cross sections as a function of $\phi^$ are measured separately for electron and muon decay channels. The cross-section is also measured double differentially as a function of $\phi^$ for three independent bins of the $Z$ boson rapidity.

Source code:ATLAS_2012_I1204784.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/DileptonFinder.hh"

namespace Rivet {

/// ATLAS Z phi* measurement class ATLAS_2012_I1204784 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(ATLAS_2012_I1204784);


/// Book histograms and initialise projections before the run
void init() {
  Cut cuts = Cuts::abseta < 2.4 && Cuts::pT > 20 * GeV;
  DileptonFinder zfinder_dressed_el(91.2 * GeV, 0.1, cuts && Cuts::abspid == PID::ELECTRON,
                                    Cuts::massIn(66 * GeV, 116 * GeV));
  declare(zfinder_dressed_el, "DileptonFinder_dressed_el");
  DileptonFinder zfinder_bare_el(91.2 * GeV, 0.0, cuts && Cuts::abspid == PID::ELECTRON,
                                 Cuts::massIn(66 * GeV, 116 * GeV));
  declare(zfinder_bare_el, "DileptonFinder_bare_el");
  DileptonFinder zfinder_dressed_mu(91.2 * GeV, 0.1, cuts && Cuts::abspid == PID::MUON,
                                    Cuts::massIn(66 * GeV, 116 * GeV));
  declare(zfinder_dressed_mu, "DileptonFinder_dressed_mu");
  DileptonFinder zfinder_bare_mu(91.2 * GeV, 0.0, cuts && Cuts::abspid == PID::MUON,
                                 Cuts::massIn(66 * GeV, 116 * GeV));
  declare(zfinder_bare_mu, "DileptonFinder_bare_mu");

  // Book histograms
  // Single-differential plots
  book(_hist_zphistar_el_bare, 1, 1, 1);
  book(_hist_zphistar_mu_bare, 1, 1, 2);
  book(_hist_zphistar_el_dressed, 2, 1, 1);
  book(_hist_zphistar_mu_dressed, 2, 1, 2);

  // Double-differential plots
  book(_h_phistar_el_bare, {0., 0.8, 1.6, 10.}, {"d03-x01-y01", "d03-x01-y02", "d03-x01-y03"});
  book(_h_phistar_el_dressed, {0., 0.8, 1.6, 10.}, {"d03-x02-y01", "d03-x02-y02", "d03-x02-y03"});
  book(_h_phistar_mu_bare, {0., 0.8, 1.6, 10.}, {"d04-x01-y01", "d04-x01-y02", "d04-x01-y03"});
  book(_h_phistar_mu_dressed, {0., 0.8, 1.6, 10.}, {"d04-x02-y01", "d04-x02-y02", "d04-x02-y03"});
}


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

  const DileptonFinder& zfinder_dressed_el = apply<DileptonFinder>(event, "DileptonFinder_dressed_el");
  fillPlots(zfinder_dressed_el, _hist_zphistar_el_dressed, _h_phistar_el_dressed);

  const DileptonFinder& zfinder_bare_el = apply<DileptonFinder>(event, "DileptonFinder_bare_el");
  fillPlots(zfinder_bare_el, _hist_zphistar_el_bare, _h_phistar_el_bare);

  const DileptonFinder& zfinder_dressed_mu = apply<DileptonFinder>(event, "DileptonFinder_dressed_mu");
  fillPlots(zfinder_dressed_mu, _hist_zphistar_mu_dressed, _h_phistar_mu_dressed);

  const DileptonFinder& zfinder_bare_mu = apply<DileptonFinder>(event, "DileptonFinder_bare_mu");
  fillPlots(zfinder_bare_mu, _hist_zphistar_mu_bare, _h_phistar_mu_bare);
}


void fillPlots(const DileptonFinder& zfind, Histo1DPtr hist, Histo1DGroupPtr& binnedHist) {
  if (zfind.bosons().size() != 1) return;
  Particles leptons = sortBy(zfind.constituents(), cmpMomByPt);

  const FourMomentum lminus = leptons[0].charge() < 0 ? leptons[0].momentum() : leptons[1].momentum();
  const FourMomentum lplus = leptons[0].charge() < 0 ? leptons[1].momentum() : leptons[0].momentum();

  const double phi_acop = M_PI - deltaPhi(lminus, lplus);
  const double costhetastar = tanh((lminus.eta() - lplus.eta()) / 2.0);
  const double sin2thetastar = (costhetastar <= 1) ? 1.0 - sqr(costhetastar) : 0;
  const double phistar = tan(phi_acop / 2.0) * sqrt(sin2thetastar);
  hist->fill(phistar);

  binnedHist->fill(zfind.bosons()[0].absrap(), phistar);
}


/// Normalise histograms etc., after the run
void finalize() {
  normalize(_hist_zphistar_el_dressed);
  normalize(_hist_zphistar_el_bare);
  normalize(_hist_zphistar_mu_dressed);
  normalize(_hist_zphistar_mu_bare);

  normalize(_h_phistar_mu_dressed);
  normalize(_h_phistar_mu_bare);
  normalize(_h_phistar_el_bare);
  normalize(_h_phistar_el_dressed);
}

private:

Histo1DGroupPtr _h_phistar_mu_dressed;
Histo1DGroupPtr _h_phistar_mu_bare;
Histo1DGroupPtr _h_phistar_el_dressed;
Histo1DGroupPtr _h_phistar_el_bare;

Histo1DPtr _hist_zphistar_el_dressed;
Histo1DPtr _hist_zphistar_el_bare;

Histo1DPtr _hist_zphistar_mu_dressed;
Histo1DPtr _hist_zphistar_mu_bare;

Histo1DPtr _hist_zphistar_el_bare_1;
Histo1DPtr _hist_zphistar_el_bare_2;
Histo1DPtr _hist_zphistar_el_bare_3;

Histo1DPtr _hist_zphistar_el_dressed_1;
Histo1DPtr _hist_zphistar_el_dressed_2;
Histo1DPtr _hist_zphistar_el_dressed_3;

Histo1DPtr _hist_zphistar_mu_bare_1;
Histo1DPtr _hist_zphistar_mu_bare_2;
Histo1DPtr _hist_zphistar_mu_bare_3;

Histo1DPtr _hist_zphistar_mu_dressed_1;
Histo1DPtr _hist_zphistar_mu_dressed_2;
Histo1DPtr _hist_zphistar_mu_dressed_3;

};

RIVET_DECLARE_PLUGIN(ATLAS_2012_I1204784);

} ```