Rivet analyses

title: BESIII_2023_I2645182

Differential decay rate in $D^+_s\to \pi^+\pi^- e^+\nu_e$

Experiment: BESIII (BEPC)

Inspire ID: 2645182

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - arXiv: 2303.12927

Beams: * *

Beam energies: ANY

Run details: - Any process producing Ds+

Differenital decay rate in $D^+_s\to \pi^+\pi^- e^+\nu_e$. Corrected data read from figure in the paper.

Source code:BESIII_2023_I2645182.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief D_s -> f0 e+ nu_e class BESIII_2023_I2645182 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2023_I2645182);


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

/// Book histograms and initialise projections before the run
void init() {
  // Initialise and register projections
  declare(UnstableParticles(Cuts::pid == 431), "UFS");
  // histos
  book(_h, 1, 1, 1);
  book(_nDs, "TMP/nDs");
}

// 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) {
  static const int mesonID = 9010221;
  // Loop over Ds mesons
  for (const Particle& p : apply<UnstableParticles>(event, "UFS").particles()) {
    _nDs->fill();
    Particle f0;
    if (isSemileptonicDecay(p, {mesonID, PID::POSITRON, PID::NU_E})) {
      f0 = select(p.children(), Cuts::pid == mesonID)[0];
      if (f0.children().size() == 2 && f0.children()[1].pid() == -f0.children()[0].pid()
          && f0.children()[0].abspid() == 211) {
        _h->fill((p.mom() - f0.mom()).mass2());
      }
    }
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  // D_s lifetime pdg2022 (ns)
  const double tau = 504e-6;
  scale(_h, 1. / tau / *_nDs);
}

/// @}


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

};

RIVET_DECLARE_PLUGIN(BESIII_2023_I2645182);

} ```