Rivet analyses

title: CLEOII_1998_I466173

Helicity angle in $D_s^+\to\rho^+\eta^\prime$

Experiment: CLEOII (CESR)

Inspire ID: 466173

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.D 58 (1998) 052002

Beams: * *

Beam energies: ANY

Run details: - Any process producing D_s+, originally e+ e-

Measurement of the helicity angle in $D_s^+\to\rho^+\eta^\prime$. The data were read from figure 9 in the paper.

Source code:CLEOII_1998_I466173.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/DecayedParticles.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief D_s+ -> eta' rho+ class CLEOII_1998_I466173 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(CLEOII_1998_I466173);


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

/// Book histograms and initialise projections before the run
void init() {
  // Initialise and register projections
  UnstableParticles ufs = UnstableParticles(Cuts::abspid == 431);
  declare(ufs, "UFS");
  DecayedParticles DS(ufs);
  DS.addStable(PID::RHOPLUS);
  DS.addStable(PID::ETAPRIME);
  declare(DS, "DS");
  // histos
  book(_h, 1, 1, 1);
}


/// Perform the per-event analysis
void analyze(const Event& event) {
  DecayedParticles DS = apply<DecayedParticles>(event, "DS");
  // loop over particles
  for (unsigned int ix = 0; ix < DS.decaying().size(); ++ix) {
    int sign = 1;
    if (DS.decaying()[ix].pid() > 0 && DS.modeMatches(ix, 2, mode))
      sign = 1;
    else if (DS.decaying()[ix].pid() < 0 && DS.modeMatches(ix, 2, modeCC))
      sign = -1;
    else
      continue;
    const Particle& rhoP = DS.decayProducts()[ix].at(sign * 213)[0];
    // rho decay products
    Particle piP;
    if (rhoP.children().size() != 2) vetoEvent;
    if (rhoP.children()[0].pid() == 211 && rhoP.children()[1].pid() == 111) {
      piP = rhoP.children()[0];
    }
    else if (rhoP.children()[1].pid() == 211 && rhoP.children()[0].pid() == 111) {
      piP = rhoP.children()[1];
    }
    else
      vetoEvent;
    // compute the helicity angle
    LorentzTransform boost1 = LorentzTransform::mkFrameTransformFromBeta(
        DS.decaying()[ix].mom().betaVec());
    FourMomentum prho = boost1.transform(rhoP.mom());
    LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(prho.betaVec());
    Vector3 axis = boost2.transform(boost1.transform(piP.mom())).p3().unit();
    _h->fill(axis.dot(prho.p3().unit()));
  }
}


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

/// @}


/// @name Histograms
/// @{
Histo1DPtr _h;
const map<PdgId, unsigned int> mode = {{213, 1}, {331, 1}};
const map<PdgId, unsigned int> modeCC = {{-213, 1}, {331, 1}};
/// @}

};

RIVET_DECLARE_PLUGIN(CLEOII_1998_I466173);

} ```