Rivet analyses

title: BABAR_2007_I1091435

$D^0\to K^- e^+\nu_e$ $q^2$ spectrum

Experiment: BABAR (PEP-II)

Inspire ID: 1091435

Status: VALIDATED

Authors: - Peter Richardson

References: - Phys.Rev. D76 (2007) 052005

Beams: * *

Beam energies: ANY

Run details: - Any process producing D0

Measurement of the $q^2$ spectrum in the decay $D^0\to K^- e^+\nu_e$ by BaBar.

Source code:BABAR_2007_I1091435.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief q^2 in D0 -> K- e+ nu_e decays class BABAR_2007_I1091435 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BABAR_2007_I1091435);


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

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

  // Initialise and register projections
  declare(UnstableParticles(), "UFS");

  // Book histograms
  book(_h_q2, 1, 1, 1);
}

// 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::pid == PID::D0)) {
    if (isSemileptonicDecay(p, {PID::KMINUS, PID::POSITRON, PID::NU_E})) {
      _h_q2->fill(q2(p, PID::KMINUS));
    }
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  normalize(_h_q2, 1.);
}

/// @}


/// @name Histograms
/// @{
Histo1DPtr _h_q2;
/// @}

};

RIVET_DECLARE_PLUGIN(BABAR_2007_I1091435);

} ```