Rivet analyses

title: CLEOC_2011_I875526

$q^2$ spectra in semi-leptonic $D^+\to\eta$ decays

Experiment: CLEOC (CESR)

Inspire ID: 875526

Status: VALIDATED

Authors: - Peter Richardson

References: - Phys.Rev. D84 (2011) 032001

Beams: * *

Beam energies: ANY

Run details: - any process producing D+ mesons

Measurement of the $q^2$ spectra for semi-leptonic $D^+\to\eta$ meson decays by CLEOC.

Source code:CLEOC_2011_I875526.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief D -> eta semi-leptonic q^2 class CLEOC_2011_I875526 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(CLEOC_2011_I875526);


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

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

  // Initialise and register projections
  declare(UnstableParticles(), "UFS");
  // histograms
  book(_h_q2_Dp_eta_A, 1, 1, 1);
  book(_h_q2_Dp_eta_B, 1, 1, 2);
  book(_nDp, "TMP/nDp");
}

// 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 D mesons
  for (const Particle& p : apply<UnstableParticles>(event, "UFS").particles(Cuts::abspid == PID::DPLUS)) {
    _nDp->fill();
    if (isSemileptonicDecay(p, {PID::ETA, PID::POSITRON, PID::NU_E})
        || isSemileptonicDecay(p, {PID::ETA, PID::ELECTRON, PID::NU_EBAR})) {
      double q = q2(p, PID::ETA);
      _h_q2_Dp_eta_A->fill(q);
      _h_q2_Dp_eta_B->fill(q);
    }
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  scale(_h_q2_Dp_eta_A, 1. / *_nDp);
  scale(_h_q2_Dp_eta_B, 1. / *_nDp);
}

/// @}


/// @name Histograms
/// @{
Histo1DPtr _h_q2_Dp_eta_A, _h_q2_Dp_eta_B;
CounterPtr _nD0, _nDp;
/// @}

};

RIVET_DECLARE_PLUGIN(CLEOC_2011_I875526);

} ```