Rivet analyses

title: CLEO_1990_I281039

$D_1(2420)^0$ and $D_2^*(2460)^0$ decay angle distributions

Experiment: CLEO (CESR)

Inspire ID: 281039

Status: VALIDATED

Authors: - Peter Richardson

References: - Phys.Rev. D41 (1990) 774

Beams: e- e+

Beam energies: (5.2, 5.2)GeV

Run details: none listed

Measurement of the $D_1(2420)^0$ and $D^_2(2460)^0$ mesons at 10.5 GeV. The decay angle of the $D^{+}$ with respect to the $D_1(2420)^0$ or $D^*_2(2460)^0$ direction in the rest frame of the parent hadron, is measured. This gives information on the spin of the parent.

Source code:CLEO_1990_I281039.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/FastJets.hh"

include "Rivet/Projections/FinalState.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief D_1 D*2 decay angle class CLEO_1990_I281039 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(CLEO_1990_I281039);


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

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

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

  // Book histograms
  book(_h_D1, 1, 1, 1);
  book(_h_D2, 1, 1, 2);
}

/// Recursively walk the decay tree to find decay products of @a p
void findDecayProducts(Particle mother, Particles& dstar, Particles& pi, unsigned int& ncount) {
  for (const Particle& p : mother.children()) {
    if (p.abspid() == 413)
      dstar.push_back(p);
    else if (p.abspid() == 211)
      pi.push_back(p);
    ncount += 1;
  }
}

/// Perform the per-event analysis
void analyze(const Event& event) {
  for (const Particle& p :
       apply<UnstableParticles>(event, "UFS").particles(Cuts::abspid == 425 || Cuts::abspid == 10423)) {
    // decay products
    Particles dstar, pi;
    unsigned int ncount = 0;
    findDecayProducts(p, dstar, pi, ncount);
    if (ncount != 2 || dstar.size() != 1 || pi.size() != 1) continue;
    if (dstar[0].pid() / p.pid() < 0) continue;
    LorentzTransform boost = LorentzTransform::mkFrameTransformFromBeta(p.momentum().betaVec());
    Vector3 axis = boost.transform(dstar[0].momentum()).p3().unit();
    double cosL = axis.dot(p.momentum().p3().unit());
    // decay angles
    if (p.abspid() == 425)
      _h_D2->fill(cosL);
    else
      _h_D1->fill(cosL);
  }
}


/// Normalise histograms etc., after the run
void finalize() {

  normalize(_h_D1);
  normalize(_h_D2);
}

/// @}


/// @name Histograms
/// @{
Histo1DPtr _h_D1, _h_D2;
/// @}

};

RIVET_DECLARE_PLUGIN(CLEO_1990_I281039);

} ```