Rivet analyses

title: BELLE_2007_I723916

Decay angles for $\Lambda_c(2880)^+\to\Sigma_c^{0,++}\pi^{+,-}$

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 $\Lambda_c(2880)^+\to\Sigma_c^{0,++}\pi^{+,-}$. 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++ // -- 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);

} ```