Rivet analyses

title: BELLE_2021_I1859517

Decay asymmetries in $\Xi^0_c\to\Lambda^0\bar{K}^{0}$, $\Sigma^0\bar{K}^{0}$ and $\Sigma^+\bar{K}^{*-}$

Experiment: BELLE (KEKB)

Inspire ID: 1859517

Status: VALIDATED

Authors: - Peter Richardson

References: - arXiv: 2104.10361

Beams: * *

Beam energies: ANY

Run details: - Any process producing Xi_c0

Measurement of the decay asymmetries in $\Xi^0_c\to\Lambda^0\bar{K}^{0}$, $\Sigma^0\bar{K}^{0}$ and $\Sigma^+\bar{K}^{*-}$ decays by the BELLE experiment.

Source code:BELLE_2021_I1859517.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief Xi_c0 decay asymmetries class BELLE_2021_I1859517 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BELLE_2021_I1859517);


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

/// Book histograms and initialise projections before the run
void init() {
  // Initialise and register projections
  declare(UnstableParticles(), "UFS");
  // book histograms
  book(_h_Lambda, 1, 1, 1);
  book(_h_Sigma0, 2, 1, 1);
  book(_h_Sigmap, 3, 1, 1);
}


/// Perform the per-event analysis
void analyze(const Event& event) {
  // loop over Xi_c0 baryons
  for (const Particle& Xic : apply<UnstableParticles>(event, "UFS").particles(Cuts::abspid == 4132)) {
    int sign = Xic.pid() / 4132;
    if (Xic.children().size() != 2) continue;
    Particle baryon1, meson1;
    if (Xic.children()[0].pid() == sign * 3122 && Xic.children()[1].pid() == -sign * 313) {
      baryon1 = Xic.children()[0];
      meson1 = Xic.children()[1];
    }
    else if (Xic.children()[1].pid() == sign * 3122 && Xic.children()[0].pid() == -sign * 313) {
      baryon1 = Xic.children()[1];
      meson1 = Xic.children()[0];
    }
    else if (Xic.children()[0].pid() == sign * 3212 && Xic.children()[1].pid() == -sign * 313) {
      baryon1 = Xic.children()[0];
      meson1 = Xic.children()[1];
    }
    else if (Xic.children()[1].pid() == sign * 3212 && Xic.children()[0].pid() == -sign * 313) {
      baryon1 = Xic.children()[1];
      meson1 = Xic.children()[0];
    }
    else if (Xic.children()[0].pid() == sign * 3222 && Xic.children()[1].pid() == -sign * 323) {
      baryon1 = Xic.children()[0];
      meson1 = Xic.children()[1];
    }
    else if (Xic.children()[1].pid() == sign * 3222 && Xic.children()[0].pid() == -sign * 323) {
      baryon1 = Xic.children()[1];
      meson1 = Xic.children()[0];
    }
    else
      continue;
    Particle baryon2, meson2;
    if (baryon1.abspid() == 3122) {
      if (baryon1.children()[0].pid() == sign * 2212 && baryon1.children()[1].pid() == -sign * 211) {
        baryon2 = baryon1.children()[0];
        meson2 = baryon1.children()[1];
      }
      else if (baryon1.children()[1].pid() == sign * 2212 && baryon1.children()[0].pid() == -sign * 211) {
        baryon2 = baryon1.children()[1];
        meson2 = baryon1.children()[0];
      }
      else
        continue;
    }
    else if (baryon1.abspid() == 3212) {
      if (baryon1.children()[0].pid() == sign * 3122 && baryon1.children()[1].pid() == 22) {
        baryon2 = baryon1.children()[0];
        meson2 = baryon1.children()[1];
      }
      else if (baryon1.children()[1].pid() == sign * 3122 && baryon1.children()[0].pid() == 22) {
        baryon2 = baryon1.children()[1];
        meson2 = baryon1.children()[0];
      }
      else
        continue;
    }
    else if (baryon1.abspid() == 3222) {
      if (baryon1.children()[0].pid() == sign * 2212 && baryon1.children()[1].pid() == 111) {
        baryon2 = baryon1.children()[0];
        meson2 = baryon1.children()[1];
      }
      else if (baryon1.children()[1].pid() == sign * 2212 && baryon1.children()[0].pid() == 111) {
        baryon2 = baryon1.children()[1];
        meson2 = baryon1.children()[0];
      }
      else
        continue;
    }
    // first boost to the Xic rest frame
    LorentzTransform boost1 = LorentzTransform::mkFrameTransformFromBeta(Xic.momentum().betaVec());
    FourMomentum pbaryon1 = boost1.transform(baryon1.momentum());
    FourMomentum pbaryon2 = boost1.transform(baryon2.momentum());
    // to lambda rest frame
    LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(pbaryon1.betaVec());
    Vector3 axis = pbaryon1.p3().unit();
    FourMomentum pp = boost2.transform(pbaryon2);
    // calculate angle
    double cTheta = pp.p3().unit().dot(axis);
    if (baryon1.abspid() == 3122) {
      _h_Lambda->fill(cTheta);
    }
    else if (baryon1.abspid() == 3212) {
      _h_Sigma0->fill(cTheta);
    }
    else if (baryon1.abspid() == 3222) {
      _h_Sigmap->fill(cTheta);
    }
  }
}

pair<double, double> calcAlpha(Histo1DPtr hist) {
  if (hist->numEntries() == 0.) return make_pair(0., 0.);
  double sum1(0.), sum2(0.);
  for (const auto& bin : hist->bins()) {
    double Oi = bin.sumW();
    if (Oi == 0.) continue;
    double ai = 0.5 * (bin.xMax() - bin.xMin());
    double bi = 0.5 * ai * (bin.xMax() + bin.xMin());
    double Ei = bin.errW();
    sum1 += sqr(bi / Ei);
    sum2 += bi / sqr(Ei) * (Oi - ai);
  }
  return make_pair(sum2 / sum1, sqrt(1. / sum1));
}

/// Normalise histograms etc., after the run
void finalize() {
  // Lambda Kbar*0
  normalize(_h_Lambda);
  Estimate0DPtr _h_alpha;
  book(_h_alpha, 4, 1, 1);
  pair<double, double> alpha = calcAlpha(_h_Lambda);
  _h_alpha->set(alpha.first, alpha.second);
  // Sigma0 Kbar*0
  normalize(_h_Sigma0);
  book(_h_alpha, 4, 1, 2);
  alpha = calcAlpha(_h_Sigma0);
  _h_alpha->set(alpha.first, alpha.second);
  // Sigma+ K*-
  normalize(_h_Sigmap);
  book(_h_alpha, 4, 1, 3);
  alpha = calcAlpha(_h_Sigmap);
  _h_alpha->set(alpha.first, alpha.second);
}

///@}


/// @name Histograms
///@{
Histo1DPtr _h_Lambda, _h_Sigma0, _h_Sigmap;
///@}

};

RIVET_DECLARE_PLUGIN(BELLE_2021_I1859517);

} ```