Rivet analyses

title: BELLE_2022_I2169621

Exclusive semileptonic $B$ to $D$ decays.

Experiment: BELLE (KEKB)

Inspire ID: 2169621

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - arXiv: 2210.13143

Beams: * *

Beam energies: ANY

Run details: - Any process

Measurement of the differential partial width with respect to $w$ for $B$ to $D$ semi-leptonic decays.

Source code:BELLE_2022_I2169621.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief B -> D semileptonic class BELLE_2022_I2169621 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BELLE_2022_I2169621);


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

/// Book histograms and initialise projections before the run
void init() {
  // projection
  declare(UnstableParticles(Cuts::pid == 511 or Cuts::pid == 521), "UFS");
  // histograms
  for (unsigned int ix = 0; ix < 4; ++ix) book(_h[ix], 1, 1, 1 + ix);
  for (unsigned int ix = 0; ix < 2; ++ix) book(_nB[ix], "TMP/nB_" + toString(ix));
}

// 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) {
  for (const Particle& p : apply<UnstableParticles>(event, "UFS").particles()) {
    if (p.children().size() <= 1) continue;
    if (p.pid() == PID::BPLUS) {
      _nB[0]->fill();
      if (isSemileptonicDecay(p, {PID::D0BAR, PID::POSITRON, PID::NU_E}))
        _h[0]->fill(recoilW(p, PID::D0BAR));
      if (isSemileptonicDecay(p, {PID::D0BAR, PID::ANTIMUON, PID::NU_MU}))
        _h[1]->fill(recoilW(p, PID::D0BAR));
    }
    else if (p.pid() == PID::B0) {
      _nB[1]->fill();
      if (isSemileptonicDecay(p, {PID::DMINUS, PID::POSITRON, PID::NU_E}))
        _h[2]->fill(recoilW(p, PID::DMINUS));
      if (isSemileptonicDecay(p, {PID::DMINUS, PID::ANTIMUON, PID::NU_MU}))
        _h[3]->fill(recoilW(p, PID::DMINUS));
    }
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  double tau[2] = {1638e-15, 1519e-15};
  double hbar = 6.582119569e-10;
  for (unsigned int ix = 0; ix < 4; ++ix) {
    double fact = ix < 2 ? hbar / tau[0] : hbar / tau[1];
    CounterPtr c = ix < 2 ? _nB[0] : _nB[1];
    scale(_h[ix], fact / *c);
  }
}

/// @}


/// @name Histograms
/// @{
Histo1DPtr _h[4];
CounterPtr _nB[2];
/// @}

};

RIVET_DECLARE_PLUGIN(BELLE_2022_I2169621);

} ```