Rivet analyses

title: ALEPH_1997_I427131

$\pi^0$ spectrum at LEP1

Experiment: ALEPH (LEP)

Inspire ID: 427131

Status: VALIDATED

Authors: - Peter Richardson

References: - Z.Phys. C74 (1997) 451-461

Beams: e- e+

Beam energies: (45.6, 45.6)GeV

Run details: - e+e- -> hadrons at Z pole

Measurement of the $\pi^0$ spectrum, and distribution of $p_T^{\text{in}}$ and $p_T^{\text{out}}$ with respect to the sphericity axis by the ALEPH experiment at LEP1.

Source code:ALEPH_1997_I427131.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/Beam.hh"

include "Rivet/Projections/FinalState.hh"

include "Rivet/Projections/Sphericity.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief pi0 spectrum class ALEPH_1997_I427131 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(ALEPH_1997_I427131);


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

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

  // // Initialise and register projections
  declare(Beam(), "Beams");
  const FinalState fs;
  declare(fs, "FS");
  declare(Sphericity(fs), "Sphericity");
  declare(UnstableParticles(), "UFS");

  // Book histograms
  book(_h_x, 2, 1, 2);
  book(_h_in, 4, 1, 1);
  book(_h_out, 3, 1, 1);
}


/// Perform the per-event analysis
void analyze(const Event& event) {
  const FinalState& fs = apply<FinalState>(event, "FS");
  if (fs.particles().size() < 2) {
    MSG_DEBUG("Failed ncharged cut");
    vetoEvent;
  }
  MSG_DEBUG("Passed ncharged cut");

  const Sphericity& sphericity = apply<Sphericity>(event, "Sphericity");

  // 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);

  for (const Particle& p : apply<UnstableParticles>(event, "UFS").particles(Cuts::pid == 111)) {
    const Vector3 mom3 = p.p3();
    const double pTinS = abs(dot(mom3, sphericity.sphericityMajorAxis()));
    const double pToutS = abs(dot(mom3, sphericity.sphericityMinorAxis()));
    _h_x->fill(mom3.mod() / meanBeamMom);
    _h_in->fill(pTinS);
    _h_out->fill(pToutS);
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  scale(_h_x, 1. / sumOfWeights());
  scale(_h_in, 1. / sumOfWeights());
  scale(_h_out, 1. / sumOfWeights());
}

/// @}


/// @name Histograms
/// @{
Histo1DPtr _h_x, _h_in, _h_out;
/// @}

};

RIVET_DECLARE_PLUGIN(ALEPH_1997_I427131);

} ```