Rivet analyses

title: BELLE_2015_I1397632

Exclusive semileptonic $B$ to $D$ decays.

Experiment: BELLE (KEKB)

Inspire ID: 1397632

Status: VALIDATED

Authors: - Holger Schulz

References: none listed

Beams: * *

Beam energies: ANY

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

Implementation of Lorentz invariant recoil w distributions for semileptonic B decays

Source code:BELLE_2015_I1397632.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief B -> D semi-leptonic class BELLE_2015_I1397632 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BELLE_2015_I1397632);


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

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

  // Initialise and register projections

  declare(UnstableParticles(), "UFS");

  // Book histograms
  book(_h_B_Denu, 1, 1, 1);
  book(_h_B_Dmunu, 1, 1, 2);
  book(_h_B_Deplusnu, 2, 1, 1);
  book(_h_B_Dmuplusnu, 2, 1, 2);
  book(_wB0, "/TMP/wB0");
  book(_wBPlus, "/TMP/wBPlus");
}

// 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; });
}

// Calculate the recoil w using mother and daugher meson
double recoilW(const Particle& B, int mesonID) {
  // TODO why does that not work with const?
  Particle D = select(B.children(), Cuts::pid == mesonID)[0];
  FourMomentum q = B.mom() - D.mom();
  return (B.mom() * B.mom() + D.mom() * D.mom() - q * q)
      / (2. * sqrt(B.mom() * B.mom()) * sqrt(D.mom() * D.mom()));
}


/// Perform the per-event analysis
void analyze(const Event& event) {
  // Get B0 Mesons
  for (const Particle& p : apply<UnstableParticles>(event, "UFS").particles(Cuts::pid == PID::B0)) {
    _wB0->fill();
    if (isSemileptonicDecay(p, {PID::DMINUS, PID::POSITRON, PID::NU_E}))
      _h_B_Denu->fill(recoilW(p, PID::DMINUS));
    if (isSemileptonicDecay(p, {PID::DMINUS, PID::ANTIMUON, PID::NU_MU}))
      _h_B_Dmunu->fill(recoilW(p, PID::DMINUS));
  }
  // Get B+ Mesons
  for (const Particle& p : apply<UnstableParticles>(event, "UFS").particles(Cuts::pid == PID::BPLUS)) {
    _wBPlus->fill();
    if (isSemileptonicDecay(p, {PID::D0BAR, PID::POSITRON, PID::NU_E}))
      _h_B_Deplusnu->fill(recoilW(p, PID::D0BAR));
    if (isSemileptonicDecay(p, {PID::D0BAR, PID::ANTIMUON, PID::NU_MU}))
      _h_B_Dmuplusnu->fill(recoilW(p, PID::D0BAR));
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  const double hbar = 6.582119569e-25;
  const double t0 = 1.519e-12, tPlus = 1.638e-12;
  scale(_h_B_Denu, 1e15 * hbar / t0 / *_wB0);
  scale(_h_B_Dmunu, 1e15 * hbar / t0 / *_wB0);
  scale(_h_B_Deplusnu, 1e15 * hbar / tPlus / *_wBPlus);
  scale(_h_B_Dmuplusnu, 1e15 * hbar / tPlus / *_wBPlus);
}

/// @}

private:

/// @name Histograms
/// @{
CounterPtr _wB0, _wBPlus;
Histo1DPtr _h_B_Denu;
Histo1DPtr _h_B_Dmunu;
Histo1DPtr _h_B_Deplusnu;
Histo1DPtr _h_B_Dmuplusnu;
/// @}

};

RIVET_DECLARE_PLUGIN(BELLE_2015_I1397632);

} ```