Rivet analyses

title: BESIII_2024_I2839350

$D^+\to \eta^\prime \ell^+\nu_\ell$

Experiment: BESIII ()

Inspire ID: 2839350

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.Lett. 134 (2025) 11, 111801 - arXiv: 2410.08603

Beams: * *

Beam energies: ANY

Run details: - Any process producing D+

Measurement of the $q^2$ spectrum in the decay $D^+\to \eta^\prime \ell^+\nu_\ell$ BES-III.

Source code:BESIII_2024_I2839350.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief D+ -> eta' ell nu class BESIII_2024_I2839350 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2024_I2839350);


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

/// Book histograms and initialise projections before the run
void init() {
  declare(UnstableParticles(Cuts::abspid == 411), "UFS");

  for (unsigned int ix = 0; ix < 2; ++ix)
    book(_h[ix], "TMP/h_" + toString(ix + 1), refData(1, 1, 1 + ix));
  book(_c, "TMP/c_Dplus");
}

// Calculate the Q2 using mother and daugher meson
double q2(const Particle& B, int mesonID) {
  FourMomentum q = B.mom() - select(B.children(), Cuts::pid == mesonID)[0];
  return q * q;
}

// Check for explicit decay into pdgids
bool isSemileptonicDecay(const Particle& mother, vector<int> ids) {
  // 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) {
  // Loop over D+ mesons
  for (const Particle& p : apply<UnstableParticles>(event, "UFS").particles()) {
    // remove particles from radiation/mixing
    bool self = false;
    for (const Particle& child : p.children()) self |= p.abspid() == child.pid();
    if (self) continue;
    _c->fill();
    if (isSemileptonicDecay(p, {PID::ETAPRIME, PID::EPLUS, PID::NU_E})) {
      _h[1]->fill(q2(p, PID::ETAPRIME));
    }
    else if (isSemileptonicDecay(p, {PID::ETAPRIME, PID::ANTIMUON, PID::NU_MU})) {
      _h[0]->fill(q2(p, PID::ETAPRIME));
    }
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  double tau = 1033e-6;
  for (unsigned int ix = 0; ix < 2; ++ix) {
    Estimate1DPtr tmp;
    book(tmp, 1, 1, 1 + ix);
    barchart(_h[ix], tmp);
    scale(tmp, 1. / tau / *_c);
  }
}

/// @}


/// @name Histograms
/// @{
Histo1DPtr _h[2];
CounterPtr _c;
/// @}

};

RIVET_DECLARE_PLUGIN(BESIII_2024_I2839350);

} ```