Rivet analyses

title: ARGUS_1989_I268577

Spectrum and decay angle for $D^0_{2}$ production in $e^+e^-$ at 10 GeV in the continuum

Experiment: ARGUS (DORIS)

Inspire ID: 268577

Status: VALIDATED

Authors: - Peter Richardson

References: - Phys.Lett. B221 (1989) 422-426

Beams: e- e+

Beam energies: (5.0, 5.0)GeV

Run details: - $e^+ e^-$ analysis near the $\Upsilon$ resonances

Measurement of the $D^_2(2460)^0$ spectrum in $e^+e^-$ collisions at 10 GeV. The decay angle of the $D^{+}$ with respect to the $D^_2(2460)^0$ direction in the rest frame of the parent hadron, this gives information on the spin of the parent, is also measured.

Source code:ARGUS_1989_I268577.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief D*2 spectrum and decay angle class ARGUS_1989_I268577 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(ARGUS_1989_I268577);


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

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

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

  // Book histograms
  book(_h_rate, 1, 1, 1);
  book(_h_D2_x, 2, 1, 1);
  book(_h_D2_ctheta, 3, 1, 1);
}


/// Recursively walk the decay tree to find decay products of @a p
void findDecayProducts(Particle mother, Particles& d, Particles& pi, unsigned int& ncount) {
  for (const Particle& p : mother.children()) {
    if (p.abspid() == 411)
      d.push_back(p);
    else if (p.abspid() == 211)
      pi.push_back(p);
    ncount += 1;
  }
}

/// Perform the per-event analysis
void analyze(const Event& event) {

  if (sedges.empty()) {
    sedges = _h_D2_x->xEdges();
  }

  const UnstableParticles& ufs = apply<UnstableParticles>(event, "UFS");
  for (const Particle& p : ufs.particles(Cuts::abspid == 425)) {
    const double xp = 2. * p.p3().mod() / sqrtS();
    const size_t idx = axisMap.index(xp) - 1;
    _h_D2_x->fill(sedges[idx]);
    // decay products
    Particles d, pi;
    unsigned int ncount = 0;
    findDecayProducts(p, d, pi, ncount);
    if (ncount != 2 || d.size() != 1 || pi.size() != 1) continue;
    if (d[0].pid() / p.pid() < 0) continue;
    LorentzTransform boost = LorentzTransform::mkFrameTransformFromBeta(p.momentum().betaVec());
    Vector3 axis = boost.transform(pi[0].momentum()).p3().unit();
    double cosL = axis.dot(p.momentum().p3().unit());
    // decay angles
    _h_D2_ctheta->fill(cosL);
    _h_rate->fill(10);
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  normalize(_h_D2_x);
  for (auto& b : _h_D2_x->bins()) {
    b.scaleW(1. / axisMap.width(b.index()));
  }
  normalize(_h_D2_ctheta);
  // br of D mode used from PDG2018
  const double br = 0.0898;
  scale(_h_rate, br / sumOfWeights() * crossSection() / picobarn);
}

/// @}


/// @name Histograms
/// @{
BinnedHistoPtr<int> _h_rate;
BinnedHistoPtr<string> _h_D2_x;
Histo1DPtr _h_D2_ctheta;
vector<string> sedges;
YODA::Axis<double> axisMap{0.0, 0.5, 0.6, 0.7, 0.85, 1.0};
/// @}

};

RIVET_DECLARE_PLUGIN(ARGUS_1989_I268577);

} ```