Rivet analyses

title: BELLE_2022_I2163247

Exclusive semileptonic $B^0\to\pi^-$ decays.

Experiment: BELLE (KEKB)

Inspire ID: 2163247

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - arXiv: 2210.04224

Beams: * *

Beam energies: ANY

Run details: - Any process producing B0, original e+ e- at Upsilon(4S)

Differential branching ratio, with respect to $q^2$ for the decays $B^0\to\pi^-\ell^+\nu_\ell$

Source code:BELLE_2022_I2163247.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief B0 -> pi - l+ nu_l class BELLE_2022_I2163247 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BELLE_2022_I2163247);


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

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

  // Initialise and register projections
  declare(UnstableParticles(Cuts::pid == PID::B0), "UFS");
  // histograms
  for (unsigned int ix = 0; ix < 3; ++ix) book(_h[ix], 1, 1, 1 + ix);
  book(_nB, "TMP/nb");
}

// 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 B0 mesons
  for (const Particle& p : apply<UnstableParticles>(event, "UFS").particles()) {
    _nB->fill();
    if (isSemileptonicDecay(p, {PID::PIMINUS, PID::POSITRON, PID::NU_E})) {
      double qq = q2(p, PID::PIMINUS);
      _h[0]->fill(qq);
      _h[2]->fill(qq);
    }
    else if (isSemileptonicDecay(p, {PID::PIMINUS, PID::ANTIMUON, PID::NU_MU})) {
      double qq = q2(p, PID::PIMINUS);
      _h[1]->fill(qq);
      _h[2]->fill(qq);
    }
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  for (unsigned int ix = 0; ix < 3; ++ix) {
    double fact = 1e4;
    if (ix == 2) fact /= 2;
    scale(_h[ix], fact / *_nB);
  }
}

/// @}


/// @name Histograms
/// @{
Histo1DPtr _h[3];
CounterPtr _nB;
/// @}

};

RIVET_DECLARE_PLUGIN(BELLE_2022_I2163247);

} ```