Rivet analyses

Differential decay rate in D0 → a0(980)−( → ηπ−)e+νe

Experiment: BESIII (BEPC)

Inspire ID: 2847417

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - arXiv: 2411.07730

Beams: * *

Beam energies: ANY

Run details: - Any process producing D0

Differential decay rate in D0 → a0(980)−( → ηπ−)e+νe. Data from table in paper.

Source code:BESIII_2024_I2847417.cc

// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {


  /// @brief D0 -> a0- e+ nu_e
  class BESIII_2024_I2847417 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2024_I2847417);


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

    /// Book histograms and initialise projections before the run
    void init() {
      // Initialise and register projections
      declare(UnstableParticles(Cuts::pid == 421), "UFS");
      // histos
      book(_h, 1, 1, 1);
      book(_nD0, "TMP/nD0");
    }

    // Check for explicit decay into pdgids
    bool isSemileptonicDecay(const Particle& mother, vector<int> ids) const {
      // Trivial check to ignore any other decays but the one in question modulo photons
      const Particles children = mother.children(Cuts::pid != PID::PHOTON);
      if (children.size() != ids.size()) return false;
      // Check for the explicit decay
      return all(ids, [&](int i) { return count(children, hasPID(i)) == 1; });
    }

    /// Perform the per-event analysis
    void analyze(const Event& event) {
      static const int mesonID = -9000211;
      // Loop over D0 mesons
      for (const Particle& p : apply<UnstableParticles>(event, "UFS").particles()) {
        _nD0->fill();
        Particle a0;
        if (isSemileptonicDecay(p, {mesonID, PID::POSITRON, PID::NU_E})) {
          a0 = select(p.children(), Cuts::pid == mesonID)[0];
          if (a0.children().size() == 2
              && ((a0.children()[0].pid() == 221 && a0.children()[1].pid() == -211)
                  || (a0.children()[1].pid() == 221 && a0.children()[0].pid() == -211))) {
            _h->fill((p.mom() - a0.mom()).mass2());
          }
        }
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      // D0  lifetime pdg2024 (ns)
      const double tau = 410.3e-6;
      scale(_h, 1.9 / tau / *_nD0);
    }

    /// @}


    /// @name Histograms
    /// @{
    Histo1DPtr _h;
    CounterPtr _nD0;
    /// @}
  };


  RIVET_DECLARE_PLUGIN(BESIII_2024_I2847417);

}