Rivet analyses

title: BESIII_2024_I2847417

Differential decay rate in $D^0\to a_0(980)^-(\to\eta\pi^-) e^+\nu_e$

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 $D^0\to a_0(980)^-(\to\eta\pi^-) e^+\nu_e$. Data from table in paper.

Source code:BESIII_2024_I2847417.cc

```c++ // -- 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);

} ```