Rivet analyses

title: BELLE_2024_I2810686

Differential branching ratio in $B^0\to\pi^-\ell^+\nu_\ell$ and $B^+\to\rho^0\ell^+\nu_\ell$

Experiment: BELLE (KEKB)

Inspire ID: 2810686

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: none listed

Beams: * *

Beam energies: ANY

Run details: - Events with B-decays, either particle guns or collisions, originally e+e- at the Upsilon(4S)

Differential branching ratio in $B^0\to\pi^-\ell^+\nu_\ell$ and $B^+\to\rho^0\ell^+\nu_\ell$

Source code:BELLE_2024_I2810686.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief B0 -> pi- and B+ rho0 semi-leptonic class BELLE_2024_I2810686 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BELLE_2024_I2810686);


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

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

  // Initialise and register projections
  declare(UnstableParticles(), "UFS");
  for (unsigned int ix = 0; ix < 2; ++ix) {
    book(_h[ix], 1, 1, 1 + ix);
    book(_c[ix], "TMP/c_" + toString(ix));
  }
}

// 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(Cuts::abspid == PID::B0)) {
    _c[0]->fill();
    if (p.pid() < 0) {
      if (isSemileptonicDecay(p, {PID::PIPLUS, PID::ELECTRON, PID::NU_EBAR})
          || isSemileptonicDecay(p, {PID::PIPLUS, PID::MUON, PID::NU_MUBAR})) {
        _h[0]->fill(q2(p, PID::PIPLUS));
      }
    }
    else {
      if (isSemileptonicDecay(p, {PID::PIMINUS, PID::POSITRON, PID::NU_E})
          || isSemileptonicDecay(p, {PID::PIMINUS, PID::ANTIMUON, PID::NU_MU})) {
        _h[0]->fill(q2(p, PID::PIMINUS));
      }
    }
  }
  for (const Particle& p : apply<UnstableParticles>(event, "UFS").particles(Cuts::abspid == PID::BPLUS)) {
    _c[1]->fill();
    if (p.pid() < 0) {
      if (isSemileptonicDecay(p, {PID::RHO0, PID::ELECTRON, PID::NU_EBAR})
          || isSemileptonicDecay(p, {PID::RHO0, PID::MUON, PID::NU_MUBAR})) {
        _h[1]->fill(q2(p, PID::RHO0));
      }
    }
    else {
      if (isSemileptonicDecay(p, {PID::RHO0, PID::POSITRON, PID::NU_E})
          || isSemileptonicDecay(p, {PID::RHO0, PID::ANTIMUON, PID::NU_MU})) {
        _h[1]->fill(q2(p, PID::RHO0));
      }
    }
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  for (unsigned int ix = 0; ix < 2; ++ix) {
    scale(_h[ix], 0.5e4 / *_c[ix]);
  }
}

/// @}


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

};

RIVET_DECLARE_PLUGIN(BELLE_2024_I2810686);

} ```