Rivet analyses

Decay angles for Λc(2880)+ → Σc0, ++π+, −

Experiment: BELLE (KEKB)

Inspire ID: 723916

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.Lett. 98 (2007) 262001

Beams: e+ e-

Beam energies: (5.3, 5.3)GeV

Run details: - e+e- to hadrons

Measurement of the helicity and decay angles for the decay Λc(2880)+ → Σc0, ++π+, −. The PDG code for this particle is not specified and which multiplet it belongs to is unclear. The default is to use, 4126, i.e the first spin $\frac{5}{2}$ state

Source code:BELLE_2007_I723916.cc

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

namespace Rivet {


  /// @brief Lambda_c(2880) -> Sigma_c pi
  class BELLE_2007_I723916 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BELLE_2007_I723916);


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

    /// Book histograms and initialise projections before the run
    void init() {
      declare(Beam(), "Beams");
      // set the PDG code
      _pid = getOption<double>("PID", 4126);
      // projections
      declare(UnstableParticles(Cuts::abspid == _pid), "UFS");
      for (unsigned int ix = 0; ix < 2; ++ix) book(_h[ix], 1, 1, 1 + ix);
    }


    /// Perform the per-event analysis
    void analyze(const Event& event) {
      // get the axis, direction of incoming electron
      const ParticlePair& beams = apply<Beam>(event, "Beams").beams();
      Vector3 axis;
      if (beams.first.pid() > 0)
        axis = beams.first.momentum().p3().unit();
      else
        axis = beams.second.momentum().p3().unit();
      // Get beams and average beam momentum
      const UnstableParticles& ufs = apply<UnstableParticles>(event, "UFS");
      for (const Particle& p : ufs.particles()) {
        // xp cut
        double xp = p.momentum().p3().mod() / sqrt(0.25 * sqrtS() - p.mass2());
        if (xp < .7) continue;
        // find the decay products
        int sign = p.pid() / p.abspid();
        // first decay
        if (p.children().size() != 2) continue;
        Particle Sigma, pi1;
        if ((p.children()[0].abspid() == 4222 * sign && p.children()[1].abspid() == -211 * sign)
            || (p.children()[0].abspid() == 4112 * sign && p.children()[1].abspid() == 211 * sign)) {
          Sigma = p.children()[0];
          pi1 = p.children()[1];
        }
        else if ((p.children()[1].abspid() == 4222 * sign && p.children()[0].abspid() == -211 * sign)
                 || (p.children()[1].abspid() == 4112 * sign && p.children()[0].abspid() == 211 * sign)) {
          Sigma = p.children()[1];
          pi1 = p.children()[0];
        }
        else
          continue;
        Vector3 axis1 = p.momentum().p3().unit();
        LorentzTransform boost = LorentzTransform::mkFrameTransformFromBeta(p.momentum().betaVec());
        Vector3 axis2 = boost.transform(pi1.momentum()).p3().unit();
        _h[0]->fill(axis1.dot(axis2));
        Vector3 axis3 = axis.cross(axis1).unit();
        Vector3 axis4 = axis1.cross(axis2).unit();
        double phi = acos(axis3.dot(axis4));
        _h[1]->fill(phi);
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      for (unsigned int ix = 0; ix < 2; ++ix) normalize(_h[ix]);
    }

    /// @}


    /// @name Histograms
    /// @{
    int _pid;
    Histo1DPtr _h[2];
    /// @}
  };


  RIVET_DECLARE_PLUGIN(BELLE_2007_I723916);

}