Rivet analyses

title: BESIII_2019_I1724880

Charge particle multiplicity in $\eta_c$ decays

Experiment: BESIII (BEPC)

Inspire ID: 1724880

Status: VALIDATED

Authors: - Peter Richardson

References: - arXiv: 1903.05375

Beams: * *

Beam energies: ANY

Run details: - Any process producing eta_c mesons

Measurement of the charged particle multiplicity distribution in $\eta_c$ decays by the BESIII collaboration.

Source code:BESIII_2019_I1724880.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief Charged particle multiplicity in eta_c decays class BESIII_2019_I1724880 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2019_I1724880);


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

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

  // Initialise and register projections
  declare(UnstableParticles(), "UFS");

  // Book histograms
  book(_h_n, 1, 1, 1);
}

void findChildren(const Particle& p, int& nCharged) {
  for (const Particle& child : p.children()) {
    if (child.children().empty()) {
      if (PID::isCharged(child.pid())) ++nCharged;
    }
    else
      findChildren(child, nCharged);
  }
}

/// Perform the per-event analysis
void analyze(const Event& event) {
  for (const Particle& p : apply<FinalState>(event, "UFS").particles(Cuts::pid == 441)) {
    int nCharged(0);
    findChildren(p, nCharged);
    _h_n->fill(min(nCharged, 8));
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  normalize(_h_n);
}

/// @}


/// @name Histograms
/// @{
BinnedHistoPtr<int> _h_n;
/// @}

};

RIVET_DECLARE_PLUGIN(BESIII_2019_I1724880);

} ```