Rivet analyses

Helicity angle in Ds+ → ρ+η′

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 Ds+ → ρ+η′. The data were read from figure 9 in the paper.

Source code:CLEOII_1998_I466173.cc

// -*- 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);

}