Rivet analyses

title: ATLAS_2011_I892704

Muon charge asymmetry in W events at 7 TeV in ATLAS

Experiment: ATLAS (LHC)

Inspire ID: 892704

Status: VALIDATED

Authors: - Frank Krauss - Hendrik Hoeth

References: - Expt page: ATLAS-STDM-2010-16 - arXiv: 1103.2929

Beams: p+ p+

Beam energies: (3500.0, 3500.0)GeV

Run details: - $W \to \mu\nu$ events at 7 TeV

Measurement of the muon charge asymmetry from W bosons produced in proton-proton collisions at a centre-of-mass energy of 7 TeV with ATLAS. The asymmetry is measured in the $W \to \mu$ decay mode as a function of the muon pseudorapidity using a data sample corresponding to a total integrated luminosity of 31 pb$^{-1}$.

Source code:ATLAS_2011_I892704.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/ChargedFinalState.hh"

include "Rivet/Projections/FinalState.hh"

include "Rivet/Projections/IdentifiedFinalState.hh"

include "Rivet/Projections/MissingMomentum.hh"

namespace Rivet {

/// Muon charge asymmetry in W events at 7 TeV in ATLAS class ATLAS_2011_I892704 : public Analysis { public:

RIVET_DEFAULT_ANALYSIS_CTOR(ATLAS_2011_I892704);


void init() {
  IdentifiedFinalState Muons(Cuts::abseta < 2.4 && Cuts::pT > 20 * GeV);
  Muons.acceptIdPair(PID::MUON);
  declare(Muons, "muons");

  ChargedFinalState CFS(Cuts::abseta < 2.8);
  declare(CFS, "tracks");

  MissingMomentum missmom(FinalState(Cuts::abseta < 5));
  declare(missmom, "MissingMomentum");

  /// @todo Will need to register TMP histograms for future histogramming
  book(_tmp_h_plus, "TMP/plus", refData(1, 1, 1));
  book(_tmp_h_minus, "TMP/minus", refData(1, 1, 1));
  book(_h_asym, 1, 1, 1);
}


void analyze(const Event& event) {

  const IdentifiedFinalState& muons = apply<IdentifiedFinalState>(event, "muons");
  if (muons.size() < 1) vetoEvent;
  const ChargedFinalState& tracks = apply<ChargedFinalState>(event, "tracks");

  Particles selected_muons;
  for (Particle muon : muons.particles()) {
    FourMomentum testmom = muon.momentum();
    double ptmu(testmom.pT()), ptsum(-ptmu), ratio(0.);
    for (Particle track : tracks.particles()) {
      const FourMomentum& trackmom = track.momentum();
      if (deltaR(testmom, trackmom) < 0.4) {
        ptsum += trackmom.pT();
        ratio = ptsum / ptmu;
        if (ratio > 0.2) break;
      }
    }
    if (ratio < 0.2) selected_muons.push_back(muon);
  }
  if (selected_muons.size() < 1) vetoEvent;

  const FourMomentum muonmom = selected_muons[0].momentum();
  const MissingMomentum& missmom = apply<MissingMomentum>(event, "MissingMomentum");
  FourMomentum missvec = -missmom.visibleMomentum();
  if (fabs(missvec.Et()) < 25 * GeV) vetoEvent;

  double MTW = sqrt(2 * missvec.pT() * muonmom.pT() * (1 - cos(deltaPhi(missvec.phi(), muonmom.phi()))));
  if (MTW < 40 * GeV) vetoEvent;

  Histo1DPtr& htmp = (selected_muons[0].pid() > 0) ? _tmp_h_minus : _tmp_h_plus;
  htmp->fill(muonmom.eta());
}


/// Normalise histograms etc., after the run
void finalize() {
  assert(*_tmp_h_plus == *_tmp_h_minus);
  for (size_t i = 1; i < _tmp_h_plus->numBins() + 1; ++i) {
    const double num = _tmp_h_plus->bin(i).sumW() - _tmp_h_minus->bin(i).sumW();
    const double denom = _tmp_h_plus->bin(i).sumW() + _tmp_h_minus->bin(i).sumW();
    const double relerr = _tmp_h_plus->bin(i).relErrW() + _tmp_h_minus->bin(i).relErrW();
    const double asym = (num != 0 && denom != 0) ? num / denom : 0;
    const double asym_err = (num != 0 && denom != 0) ? asym * relerr : 0;
    _h_asym->bin(i).set(asym, asym_err);
  }
}

private:

Estimate1DPtr _h_asym;
/// @todo Will need to register TMP histograms for future histogramming
Histo1DPtr _tmp_h_plus, _tmp_h_minus;

};

RIVET_DECLARE_ALIASED_PLUGIN(ATLAS_2011_I892704, ATLAS_2011_S9002537);

} ```

Aliases: - ATLAS_2011_S9002537