Rivet analyses

title: BESIII_2017_I1519425

Differential decay rates for $D^+\to {\bar{K}^0,\pi^0} e^+\nu_e$ from BES

Experiment: BESIII (BEPC II)

Inspire ID: 1519425

Status: VALIDATED

Authors: - Peter Richardson

References: - Phys.Rev. D96 (2017) no.1, 012002

Beams: * *

Beam energies: ANY

Run details: - Events with D-decays, either particle guns or collisions.

Differential decay rates for semileptonic $D^+\to \bar{K}^0,\pi^0e^+\nu_e$ decays

Source code:BESIII_2017_I1519425.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief Differential decay rates for $D^+\to {\bar{K}^0,\pi^0} e^+\nu_e$ from BES class BESIII_2017_I1519425 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2017_I1519425);


/// @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_K, 1, 1, 1);
  book(_h_q2_pi, 2, 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 D+/- mesons
  for (const Particle& p : apply<UnstableParticles>(event, "UFS").particles(Cuts::abspid == PID::DPLUS)) {
    if (isSemileptonicDecay(p, {PID::PI0, PID::POSITRON, PID::NU_E})
        || isSemileptonicDecay(p, {PID::PI0, PID::ELECTRON, PID::NU_EBAR})) {
      _h_q2_pi->fill(q2(p, PID::PI0));
    }
    else if (isSemileptonicDecay(p, {-311, PID::POSITRON, PID::NU_E})) {
      _h_q2_K->fill(q2(p, -311));
    }
    else if (isSemileptonicDecay(p, {311, PID::ELECTRON, PID::NU_EBAR})) {
      _h_q2_K->fill(q2(p, 311));
    }
    else if (isSemileptonicDecay(p, {PID::K0S, PID::POSITRON, PID::NU_E})
             || isSemileptonicDecay(p, {PID::K0S, PID::ELECTRON, PID::NU_EBAR})) {
      _h_q2_K->fill(q2(p, PID::K0S));
    }
    else if (isSemileptonicDecay(p, {PID::K0L, PID::POSITRON, PID::NU_E})
             || isSemileptonicDecay(p, {PID::K0L, PID::ELECTRON, PID::NU_EBAR})) {
      _h_q2_K->fill(q2(p, PID::K0L));
    }
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  // normalize to unity
  normalize(_h_q2_K);
  normalize(_h_q2_pi);
}

/// @}


/// @name Histograms
/// @{
Histo1DPtr _h_q2_K, _h_q2_pi;
/// @}

};

RIVET_DECLARE_PLUGIN(BESIII_2017_I1519425);

} ```