Rivet analyses

title: DELPHI_1996_I401100

Spectrum for $\pi^0$ production in hadronic $Z^0$ decays

Experiment: DELPHI (LEP)

Inspire ID: 401100

Status: VALIDATED

Authors: - Peter Richardson

References: - Z.Phys. C69 (1996) 561-574, 1996

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)

DELPHI results for the spectra of $\pi6)$ production in hadronic $Z^0$ decays, including $b\bar{b}$ initiated events.

Source code:DELPHI_1996_I401100.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/Beam.hh"

include "Rivet/Projections/ChargedFinalState.hh"

include "Rivet/Projections/FinalState.hh"

include "Rivet/Projections/UnstableParticles.hh"

define I_KNOW_THE_INITIAL_QUARKS_PROJECTION_IS_DODGY_BUT_NEED_TO_USE_IT

include "Rivet/Projections/InitialQuarks.hh"

namespace Rivet {

/// @brief pi0 spectrum class DELPHI_1996_I401100 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(DELPHI_1996_I401100);


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

/// Book histograms and initialise projections before the run
void init() {
  declare(Beam(), "Beams");
  declare(ChargedFinalState(), "FS");
  declare(UnstableParticles(), "UFS");
  declare(InitialQuarks(), "IQF");

  // Book histograms
  book(_h_pi_all, 1, 1, 1);
  book(_h_pi_bot, 3, 1, 1);

  book(_wAll, "TMP/wAll");
  book(_wBot, "TMP/wBot");
}


/// Perform the per-event analysis
void analyze(const Event& event) {
  // First, veto on leptonic events by requiring at least 4 charged FS particles
  const FinalState& fs = apply<FinalState>(event, "FS");
  const size_t numParticles = fs.particles().size();

  // Even if we only generate hadronic events, we still need a cut on numCharged >= 2.
  if (numParticles < 2) {
    MSG_DEBUG("Failed leptonic event cut");
    vetoEvent;
  }
  MSG_DEBUG("Passed leptonic event cut");

  int flavour = 0;
  const InitialQuarks& iqf = apply<InitialQuarks>(event, "IQF");

  // If we only have two quarks (qqbar), just take the flavour.
  // If we have more than two quarks, look for the highest energetic q-qbar pair.
  if (iqf.particles().size() == 2) {
    flavour = iqf.particles().front().abspid();
  }
  else {
    map<int, double> quarkmap;
    for (const Particle& p : iqf.particles()) {
      if (quarkmap[p.pid()] < p.E()) {
        quarkmap[p.pid()] = p.E();
      }
    }
    double maxenergy = 0.;
    for (int i = 1; i <= 5; ++i) {
      if (quarkmap[i] + quarkmap[-i] > maxenergy) {
        flavour = i;
      }
    }
  }

  _wAll->fill();
  if (flavour == 5) _wBot->fill();

  // Get beams and average beam momentum
  const ParticlePair& beams = apply<Beam>(event, "Beams").beams();
  const double meanBeamMom = (beams.first.p3().mod() + beams.second.p3().mod()) / 2.0;
  MSG_DEBUG("Avg beam momentum = " << meanBeamMom);

  // Final state of unstable particles to get particle spectra
  const UnstableParticles& ufs = apply<UnstableParticles>(event, "UFS");

  for (const Particle& p : ufs.particles(Cuts::pid == PID::PI0)) {
    double xp = p.p3().mod() / meanBeamMom;
    _h_pi_all->fill(xp);
    if (flavour == 5) _h_pi_bot->fill(xp);
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  scale(_h_pi_all, 1. / *_wAll);
  scale(_h_pi_bot, 1. / *_wBot);
}

/// @}


/// @name Histograms
/// @{
Histo1DPtr _h_pi_all, _h_pi_bot;
CounterPtr _wAll, _wBot;
/// @}

};

RIVET_DECLARE_PLUGIN(DELPHI_1996_I401100);

} ```