Rivet analyses

title: BESIII_2015_I1391138

Exclusive $D^0\to K^-,\pi^-e^+\nu_e$ decays

Experiment: BESIII (BEPC)

Inspire ID: 1391138

Status: VALIDATED

Authors: - Peter Richardson

References: - Phys.Rev. D92 (2015) 072012, 2015

Beams: * *

Beam energies: ANY

Run details: - Events with D-decays, either particle guns or collisions.

Differential decay rates for semileptonic $D^0\to K^-,\pi^-e^+\nu_e$ decays

Source code:BESIII_2015_I1391138.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief Exclusive $D^0\to K^-,\pi^-e^+\nu_e$ decays class BESIII_2015_I1391138 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2015_I1391138);


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

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

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

  // Book histograms
  book(_h_q2_K, 1, 1, 3);
  book(_h_q2_pi, 2, 1, 3);
  book(nD0, "TMP/DCounter");
}


// Calculate the Q2 using mother and daugher meson
size_t q2(const Particle& B, int mesonID, size_t species) const {
  FourMomentum q = B.mom() - select(B.children(), Cuts::pid == mesonID)[0];
  return axes[species].index(q * q) - 1;
}


// 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) {

  if (edges_K.empty()) edges_K = _h_q2_K->xEdges();
  if (edges_pi.empty()) edges_pi = _h_q2_pi->xEdges();

  // Loop over D0 mesons
  for (const Particle& p : apply<UnstableParticles>(event, "UFS").particles(Cuts::pid == PID::D0)) {
    nD0->fill();
    if (isSemileptonicDecay(p, {PID::PIMINUS, PID::POSITRON, PID::NU_E})) {
      _h_q2_pi->fill(edges_pi[q2(p, PID::PIMINUS, 1)]);
    }
    else if (isSemileptonicDecay(p, {PID::KMINUS, PID::POSITRON, PID::NU_E})) {
      _h_q2_K->fill(edges_K[q2(p, PID::KMINUS, 0)]);
    }
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  // scale by D0 lifetime = 410.1e-6 ps (from PDG 2014 used in paper)
  scale(_h_q2_K, 1. / dbl(*nD0) / 410.1e-6);
  scale(_h_q2_pi, 1. / dbl(*nD0) / 410.1e-6);
}

/// @}


/// @name Histograms
/// @{
BinnedHistoPtr<string> _h_q2_K, _h_q2_pi;
CounterPtr nD0;
vector<string> edges_K, edges_pi;
YODA::Axis<double> axes[2] = {YODA::Axis<double>(17, 0.0, 1.7), YODA::Axis<double>(13, 0.0, 2.6)};
/// @}

};

RIVET_DECLARE_PLUGIN(BESIII_2015_I1391138);

} ```