Rivet analyses

title: BABAR_2011_I855306

Semi-leptonic $B\to\pi\ell^+\nu_\ell$ and $B\to\rho\ell^+\nu_\ell$

Experiment: BABAR (PEP-II)

Inspire ID: 855306

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.D 83 (2011) 032007

Beams: * *

Beam energies: ANY

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

Implementation of Lorentz invariant $q^2$ distributions for $B\to\pi\ell^+\nu_\ell$ and $B\to\rho\ell^+\nu_\ell$.

Source code:BABAR_2011_I855306.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief B -> pi,rho l+ nu class BABAR_2011_I855306 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BABAR_2011_I855306);


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

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

  // Initialise and register projections
  declare(UnstableParticles(Cuts::abspid == PID::BPLUS || Cuts::abspid == PID::B0), "UFS");
  for (unsigned int ix = 0; ix < 2; ++ix) {
    book(_c[ix], "TMP/c_" + toString(ix + 1));
    for (unsigned int iy = 0; iy < 3; ++iy) {
      book(_h[ix][iy], ix + 1, 1, iy + 1);
    }
  }
}

// Calculate the Q2 using mother and daughter charged lepton
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) {
  // Get B+ Mesons
  for (const Particle& p : apply<UnstableParticles>(event, "UFS").particles()) {
    // B0 modes
    if (p.abspid() == 511) {
      _c[0]->fill();
      if (isSemileptonicDecay(p, {PID::PIMINUS, PID::POSITRON, PID::NU_E})
          || isSemileptonicDecay(p, {PID::PIMINUS, PID::ANTIMUON, PID::NU_MU})) {
        double qq = q2(p, PID::PIMINUS);
        _h[0][0]->fill(qq);
        _h[0][2]->fill(qq);
      }
      else if (isSemileptonicDecay(p, {PID::PIPLUS, PID::ELECTRON, PID::NU_EBAR})
               || isSemileptonicDecay(p, {PID::PIPLUS, PID::MUON, PID::NU_MUBAR})) {
        double qq = q2(p, PID::PIPLUS);
        _h[0][0]->fill(qq);
        _h[0][2]->fill(qq);
      }
      else if (isSemileptonicDecay(p, {PID::RHOMINUS, PID::POSITRON, PID::NU_E})
               || isSemileptonicDecay(p, {PID::RHOMINUS, PID::ANTIMUON, PID::NU_MU})) {
        double qq = q2(p, PID::RHOMINUS);
        _h[1][0]->fill(qq);
        _h[1][2]->fill(qq);
      }
      else if (isSemileptonicDecay(p, {PID::RHOPLUS, PID::ELECTRON, PID::NU_EBAR})
               || isSemileptonicDecay(p, {PID::RHOPLUS, PID::MUON, PID::NU_MUBAR})) {
        double qq = q2(p, PID::RHOPLUS);
        _h[1][0]->fill(qq);
        _h[1][2]->fill(qq);
      }
    }
    // B+ modes
    else {
      _c[1]->fill();
      if (isSemileptonicDecay(p, {PID::PI0, PID::POSITRON, PID::NU_E})
          || isSemileptonicDecay(p, {PID::PI0, PID::ANTIMUON, PID::NU_MU})
          || isSemileptonicDecay(p, {PID::PI0, PID::ELECTRON, PID::NU_EBAR})
          || isSemileptonicDecay(p, {PID::PI0, PID::MUON, PID::NU_MUBAR})) {
        _h[0][1]->fill(q2(p, PID::PI0));
      }
      else if (isSemileptonicDecay(p, {PID::RHO0, PID::POSITRON, PID::NU_E})
               || isSemileptonicDecay(p, {PID::RHO0, PID::ANTIMUON, PID::NU_MU})
               || isSemileptonicDecay(p, {PID::RHO0, PID::ELECTRON, PID::NU_EBAR})
               || isSemileptonicDecay(p, {PID::RHO0, PID::MUON, PID::NU_MUBAR})) {
        _h[1][1]->fill(q2(p, PID::RHO0));
      }
    }
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  // Br in units 10^-4 and average over e/mu modes
  for (unsigned int ix = 0; ix < 2; ++ix) {
    for (unsigned int iy = 0; iy < 3; ++iy) {
      if (iy == 1)
        scale(_h[ix][iy], 0.5 * 1e4 / *_c[1]);
      else
        scale(_h[ix][iy], 0.5 * 1e4 / *_c[0]);
    }
  }
}

/// @}


/// @name Histograms
/// @{
Histo1DPtr _h[2][3];
CounterPtr _c[2];
/// @}

};

RIVET_DECLARE_PLUGIN(BABAR_2011_I855306);

} ```