Rivet analyses

title: OPAL_2001_I552446

Four-jet angles using Durham algorithm

Experiment: OPAL (LEP Run 1)

Inspire ID: 552446

Status: VALIDATED

Authors: - Frank Siegert

References: - Eur.Phys.J.C20:601-615,2001 - DOI: 10.1007/s100520100699 - arXiv: hep-ex/0101044

Beams: e+ e-

Beam energies: (45.6, 45.6)GeV

Run details: - Hadronic Z decay events generated on the Z pole ($\sqrt{s} = 91.2$ GeV) Hadronisation should be turned off because the data is corrected back to the parton level.

Angles between the leading (in energy) four jets defined using the Durham algorithm with $y_\mathrm{cut}=0.008$. The data is presented at the parton level and includes the Bengtsson-Zerwas, Korner-Schierholz-Willrodt and Nachtmann-Reiter angles as well as the angle between the two softest jets.

Source code:OPAL_2001_I552446.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/FastJets.hh"

include "Rivet/Projections/FinalState.hh"

namespace Rivet {

/// Four-jet angles using Durham algorithm class OPAL_2001_I552446 : public Analysis { public:

RIVET_DEFAULT_ANALYSIS_CTOR(OPAL_2001_I552446);


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

/// Book histograms and initialise projections before the run
void init() {

  // Initialise and register projections
  const FinalState fs;
  declare(fs, "FS");
  declare(FastJets(fs, JetAlg::DURHAM, 0.7), "Jets");

  // Book histograms here
  book(_h_BZ, 3, 1, 1);
  book(_h_KSW, 4, 1, 1);
  book(_h_NR, 5, 1, 1);
  book(_h_ALPHA34, 6, 1, 1);
}


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

  // Even if we only generate hadronic events, we still need a cut on numCharged >= 2.
  if (apply<FinalState>(event, "FS").particles().size() < 2) {
    vetoEvent;
  }

  const FastJets& fastjets = apply<FastJets>(event, "Jets");
  if (fastjets.clusterSeq()) {
    vector<fastjet::PseudoJet> jets;
    for (const fastjet::PseudoJet& jet :
         fastjet::sorted_by_E(fastjets.clusterSeq()->exclusive_jets_ycut(0.008))) {
      if (jet.E() > 3.0 * GeV) jets.push_back(jet);
    }
    if (jets.size() == 4) {
      // Prevent nan-fill due to division by zero in calc_BZ
      double bz = fabs(calc_BZ(jets));
      if (!std::isnan(bz)) _h_BZ->fill(bz);
      _h_KSW->fill(calc_KSW(jets));
      _h_NR->fill(fabs(calc_NR(jets)));
      _h_ALPHA34->fill(calc_ALPHA34(jets));
    }
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  normalize(_h_BZ);
  normalize(_h_KSW);
  normalize(_h_NR);
  normalize(_h_ALPHA34);
}

/// @}

private:

/// @name Jet angle calculator functions
/// @{

/// @todo Use Jet or FourMomentum interface rather than PseudoJet
/// @todo Move to utils?
double calc_BZ(const vector<fastjet::PseudoJet>& jets) {
  assert(jets.size() == 4);
  Vector3 p12 = cross(momentum3(jets[0]), momentum3(jets[1]));
  Vector3 p34 = cross(momentum3(jets[2]), momentum3(jets[3]));
  return dot(p12, p34) / (p12.mod() * p34.mod());
}


/// @todo Use Jet or FourMomentum interface rather than PseudoJet
/// @todo Move to utils?
double calc_KSW(const vector<fastjet::PseudoJet>& jets) {
  assert(jets.size() == 4);
  Vector3 p13 = cross(momentum3(jets[0]), momentum3(jets[2]));
  Vector3 p24 = cross(momentum3(jets[1]), momentum3(jets[3]));
  Vector3 p14 = cross(momentum3(jets[0]), momentum3(jets[3]));
  Vector3 p23 = cross(momentum3(jets[1]), momentum3(jets[2]));
  return cos(
      0.5
      * (acos(dot(p14, p23) / (p14.mod() * p23.mod())) + acos(dot(p13, p24) / (p13.mod() * p24.mod()))));
}


/// @todo Use Jet or FourMomentum interface rather than PseudoJet
/// @todo Move to utils?
double calc_NR(const vector<fastjet::PseudoJet>& jets) {
  assert(jets.size() == 4);
  Vector3 p12 = momentum3(jets[0]) - momentum3(jets[1]);
  Vector3 p34 = momentum3(jets[2]) - momentum3(jets[3]);
  return dot(p12, p34) / (p12.mod() * p34.mod());
}

/// @todo Use Jet or FourMomentum interface rather than PseudoJet
/// @todo Move to utils?
double calc_ALPHA34(const vector<fastjet::PseudoJet>& jets) {
  assert(jets.size() == 4);
  Vector3 p3 = momentum3(jets[2]);
  Vector3 p4 = momentum3(jets[3]);
  return dot(p3, p4) / (p3.mod() * p4.mod());
}

/// @}


/// @name Histograms
/// @{
Histo1DPtr _h_BZ;
Histo1DPtr _h_KSW;
Histo1DPtr _h_NR;
Histo1DPtr _h_ALPHA34;
/// @}

};

RIVET_DECLARE_ALIASED_PLUGIN(OPAL_2001_I552446, OPAL_2001_S4553896);

} ```

Aliases: - OPAL_2001_S4553896