Rivet analyses

title: ARGUS_1989_I280943

Spectra and decay distributions for $D_1(2420)^0$ and $D^*_2(2460)^0$ production in $e^+e^-$ collisions at 10 GeV

Experiment: ARGUS (DORIS)

Inspire ID: 280943

Status: VALIDATED

Authors: - Peter Richardson

References: - Phys.Lett. B232 (1989) 398-404

Beams: e- e+

Beam energies: (5.0, 5.0)GeV

Run details: - e+e- to hadrons

Measurements of the scaled momentum spectrum for $D_1(2420)^0$ and $D^_2(2460)^0$ production in $e^+e^-$ collisions at 10 GeV. The decays $D_1(2420)^0, D^_2(2460)^0 \to D^{+}\pi^-\to D^0\pi^+\pi^-$ were used and the helicity angle, i.e. the angle between the two pions in the rest frame of the $D^$ are is measured.

Source code:ARGUS_1989_I280943.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief D_1 and D_2 spectra and decay distributions class ARGUS_1989_I280943 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(ARGUS_1989_I280943);


/// @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_rate, 1, 1, 1);
  book(_h_D2_rate, 1, 1, 2);
  book(_h_D1_x, 4, 1, 1);
  book(_h_D2_x, 4, 1, 2);
  book(_h_D1_alpha, 3, 1, 1);
  book(_h_D2_alpha, 3, 1, 2);
}

/// Recursively walk the decay tree to find decay products of @a p
void findDecayProducts(Particle mother,
                       Particles& dstar,
                       Particles& d0,
                       Particles& pi,
                       unsigned int& ncount) {
  for (const Particle& p : mother.children()) {
    if (p.abspid() == 413)
      dstar.push_back(p);
    else if (p.abspid() == 421)
      d0.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)) {
    const double xp = 2. * p.p3().mod() / sqrtS();
    // spectra
    if (p.abspid() == 425)
      _h_D2_x->fill(xp);
    else
      _h_D1_x->fill(xp);
    // decay products
    // first od D_1,D_2
    Particles dstar, d0, pi;
    unsigned int ncount = 0;
    findDecayProducts(p, dstar, d0, pi, ncount);
    if (ncount != 2 || dstar.size() != 1 || pi.size() != 1 || d0.size() != 0) continue;
    if (dstar[0].pid() / p.pid() < 0) continue;
    if (p.abspid() == 425)
      _h_D2_rate->fill(10);
    else
      _h_D1_rate->fill(10);
    Particle p2 = dstar[0];
    LorentzTransform boost = LorentzTransform::mkFrameTransformFromBeta(p2.momentum().betaVec());
    Vector3 d1 = boost.transform(pi[0].momentum()).p3().unit();
    // then of D*
    ncount = 0;
    dstar.clear();
    d0.clear();
    pi.clear();
    findDecayProducts(p2, dstar, d0, pi, ncount);
    if (ncount != 2 || dstar.size() != 0 || pi.size() != 1 || d0.size() != 1) continue;
    if (pi[0].pid() / p2.pid() < 0) continue;
    Vector3 d2 = boost.transform(pi[0].momentum()).p3().unit();
    double cosAlpha = abs(d1.dot(d2));
    // decay angles
    if (p.abspid() == 425)
      _h_D2_alpha->fill(cosAlpha);
    else
      _h_D1_alpha->fill(cosAlpha);
  }
}


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

  normalize(_h_D1_x);
  normalize(_h_D2_x);
  normalize(_h_D1_alpha);
  normalize(_h_D2_alpha);
  scale(_h_D1_rate, crossSection() / picobarn / sumOfWeights());
  scale(_h_D2_rate, crossSection() / picobarn / sumOfWeights());
}

/// @}


/// @name Histograms
/// @{
BinnedHistoPtr<int> _h_D1_rate, _h_D2_rate;
Histo1DPtr _h_D1_x, _h_D2_x;
Histo1DPtr _h_D1_alpha, _h_D2_alpha;
const int Ecms = 10;
/// @}

};

RIVET_DECLARE_PLUGIN(ARGUS_1989_I280943);

} ```