Rivet analyses

title: ARGUS_1987_I247005

Helicty angle in $D^0\to K^0_S\phi$

Experiment: ARGUS (DORIS)

Inspire ID: 247005

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Z.Phys.C 33 (1987) 359-362

Beams: * *

Beam energies: ANY

Run details: - Any process producing D0 mesons

Measurement of the helicity angle in $D^0\to K^0_S\phi$

Source code:ARGUS_1987_I247005.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/DecayedParticles.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief D0 -> KS0 phi class ARGUS_1987_I247005 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(ARGUS_1987_I247005);


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

/// Book histograms and initialise projections before the run
void init() {
  // Initialise and register projections
  UnstableParticles ufs = UnstableParticles(Cuts::abspid == 421);
  declare(ufs, "UFS");
  DecayedParticles D0(ufs);
  D0.addStable(PID::PI0);
  D0.addStable(PID::K0S);
  D0.addStable(PID::PHI);
  declare(D0, "D0");
  // histos
  book(_h, 1, 1, 1);
}


/// Perform the per-event analysis
void analyze(const Event& event) {
  DecayedParticles D0 = apply<DecayedParticles>(event, "D0");
  // loop over particles
  for (unsigned int ix = 0; ix < D0.decaying().size(); ++ix) {
    if (!D0.modeMatches(ix, 2, mode)) continue;
    //const Particle & K0  = D0.decayProducts()[ix].at(310)[0];
    const Particle& phi = D0.decayProducts()[ix].at(333)[0];
    if (phi.children().size() != 2) continue;
    if (phi.children()[0].abspid() != PID::KPLUS || phi.children()[1].abspid() != PID::KPLUS) continue;
    // first boost all relevant momenta to D0 rest frame
    LorentzTransform boost = LorentzTransform::mkFrameTransformFromBeta(D0.decaying()[ix].mom());
    FourMomentum pphi = boost.transform(phi.mom());
    FourMomentum pK = boost.transform(phi.children()[0].mom());
    LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(pphi.betaVec());
    Vector3 axis1 = pphi.p3().unit();
    Vector3 axis2 = boost2.transform(pK).p3().unit();
    _h->fill(axis1.dot(axis2));
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  normalize(_h, 1.0, false);
}

/// @}


/// @name Histograms
/// @{
Histo1DPtr _h;
const map<PdgId, unsigned int> mode = {{310, 1}, {333, 1}};
/// @}

};

RIVET_DECLARE_PLUGIN(ARGUS_1987_I247005);

} ```