Rivet analyses

Helicity angle distributions in χ_c1 → γ + (ϕ, ρ, ω)

Experiment: BESIII (BEPC)

Inspire ID: 894356

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.D 83 (2011) 112005

Beams: * *

Beam energies: ANY

Run details: - Any process producing chi_c1, originally e+e- -> psi(2S)

Measurement of the helicity angles in the decays χ_c1 → γ + (ϕ, ρ, ω). The data were read from the plots in the paper amnd may not be corrected for efficiency/acceptance, however the backgrounds given in the paper have been subtracted.

Source code:`BESIII_2011_I894356.cc`

// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {


  /// @brief chi_c1 -> gamma +V
  class BESIII_2011_I894356 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2011_I894356);


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

    /// Book histograms and initialise projections before the run
    void init() {
      // projections
      declare(UnstableParticles(Cuts::pid == 20443), "UFS");
      // histograms
      for (unsigned int ix = 0; ix < 3; ++ix) book(_h[ix], 1, 1, 1 + ix);
    }

    void findChildren(const Particle& p,
                      Particles& pim,
                      Particles& pip,
                      Particles& pi0,
                      unsigned int& ncount) {
      for (const Particle& child : p.children()) {
        if (child.pid() == PID::PIPLUS) {
          pip.push_back(child);
          ncount += 1;
        }
        else if (child.pid() == PID::PIMINUS) {
          pim.push_back(child);
          ncount += 1;
        }
        else if (child.pid() == PID::PI0) {
          pi0.push_back(child);
          ncount += 1;
        }
        else if (child.children().empty()) {
          ncount += 1;
        }
        else
          findChildren(child, pim, pip, pi0, ncount);
      }
    }

    /// Perform the per-event analysis
    void analyze(const Event& event) {
      for (const Particle& p : apply<UnstableParticles>(event, "UFS").particles()) {
        if (p.children().size() != 2) continue;
        Particle gamma, meson;
        // get the photon and the meson
        if (p.children()[0].pid() == PID::PHOTON) {
          gamma = p.children()[0];
          meson = p.children()[1];
        }
        else if (p.children()[1].pid() == PID::PHOTON) {
          gamma = p.children()[1];
          meson = p.children()[0];
        }
        else
          continue;
        // check the meson
        int imode = -1;
        if (meson.pid() == 333)
          imode = 0;
        else if (meson.pid() == 113)
          imode = 1;
        else if (meson.pid() == 223)
          imode = 2;
        else
          continue;
        Particle d1, d2, d3;
        if (imode == 0) {
          if (meson.children().size() != 2) continue;
          if (meson.children()[0].pid() == -meson.children()[1].pid()
              && meson.children()[0].abspid() == 321) {
            d1 = meson.children()[0];
            d2 = meson.children()[0];
          }
          else
            continue;
        }
        else if (imode == 1) {
          if (meson.children().size() != 2) continue;
          if (meson.children()[0].pid() == -meson.children()[1].pid()
              && meson.children()[0].abspid() == 211) {
            d1 = meson.children()[0];
            d2 = meson.children()[0];
          }
          else
            continue;
        }
        else if (imode == 2) {
          unsigned int ncount = 0;
          Particles pip, pim, pi0;
          findChildren(meson, pim, pip, pi0, ncount);
          if (ncount == 3 && pim.size() == 1 && pip.size() == 1 && pi0.size() == 1) {
            d1 = pip[0];
            d2 = pim[0];
            d3 = pi0[0];
          }
          else
            continue;
        }
        if (d1.pid() < 0) swap(d1, d2);
        // boost in chi_c1 frame
        LorentzTransform boost1 = LorentzTransform::mkFrameTransformFromBeta(p.momentum().betaVec());
        FourMomentum pMeson = boost1.transform(meson.momentum());
        FourMomentum p1 = boost1.transform(d1.momentum());
        FourMomentum p2 = boost1.transform(d2.momentum());
        Vector3 axis1 = pMeson.p3().unit();
        LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(pMeson.betaVec());
        p1 = boost2.transform(p1);
        p2 = boost2.transform(p2);
        // axis in meson rest frame
        Vector3 axis2;
        if (imode < 2) {
          axis2 = p1.p3().unit();
        }
        else {
          FourMomentum p3 = boost1.transform(d3.momentum());
          p3 = boost2.transform(p3);
          axis2 = p1.p3().cross(p2.p3()).unit();
        }
        _h[imode]->fill(axis1.dot(axis2));
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      for (unsigned int ix = 0; ix < 3; ++ix) normalize(_h[ix], 1., false);
    }

    /// @}


    /// @name Histograms
    /// @{
    Histo1DPtr _h[3];
    /// @}
  };


  RIVET_DECLARE_PLUGIN(BESIII_2011_I894356);

}

Rivet analyses

Helicity angle distributions in χc1 → γ + (ϕ, ρ, ω)

Source code:BESIII_2011_I894356.cc

Helicity angle distributions in χ_c1 → γ + (ϕ, ρ, ω)

Source code:`BESIII_2011_I894356.cc`