Rivet analyses

title: BELLE_2022_I2140379

Decay asymmetries in $\Lambda_c^+ \to \Sigma^+ \pi^0$, $\Sigma^+ \eta$, and $\Sigma^+ \eta^\prime$

Experiment: BELLE (KEKB)

Inspire ID: 2140379

Status: VALIDATED NOHEPDATA SINGLEWEIGHT

Authors: - Peter Richardson

References: - arXiv: 2208.10825

Beams: * *

Beam energies: ANY

Run details: - Any process producing Lambda_c baryons

Decay asymmetries in $\Lambda_c^+ \to \Sigma^+ \pi^0$, $\Sigma^+ \eta$, and $\Sigma^+ \eta^\prime$

Source code:BELLE_2022_I2140379.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief Lambda_c -> Sigma+ pi0,eta,eta' decay asymmetries class BELLE_2022_I2140379 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BELLE_2022_I2140379);


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

/// Book histograms and initialise projections before the run
void init() {
  // Initialise and register projections
  declare(UnstableParticles(), "UFS");
  // histograms
  for (unsigned int ix = 0; ix < 3; ++ix) book(_h[ix], 2, 1, 1 + ix);
}


/// Perform the per-event analysis
void analyze(const Event& event) {
  // loop over Lambda_c baryons
  for (const Particle& Lambdac : apply<UnstableParticles>(event, "UFS").particles(Cuts::abspid == 4122)) {
    int sign = Lambdac.pid() / 4122;
    if (Lambdac.children().size() != 2) continue;
    Particle baryon1;
    int imeson = -1;
    if (Lambdac.children()[0].pid() == sign * 3222 && Lambdac.children()[1].pid() == 111) {
      baryon1 = Lambdac.children()[0];
      imeson = 0;
    }
    else if (Lambdac.children()[1].pid() == sign * 3222 && Lambdac.children()[0].pid() == 111) {
      baryon1 = Lambdac.children()[1];
      imeson = 0;
    }
    else if (Lambdac.children()[0].pid() == sign * 3222 && Lambdac.children()[1].pid() == 221) {
      baryon1 = Lambdac.children()[0];
      imeson = 1;
    }
    else if (Lambdac.children()[1].pid() == sign * 3222 && Lambdac.children()[0].pid() == 221) {
      baryon1 = Lambdac.children()[1];
      imeson = 1;
    }
    else if (Lambdac.children()[0].pid() == sign * 3222 && Lambdac.children()[1].pid() == 331) {
      baryon1 = Lambdac.children()[0];
      imeson = 2;
    }
    else if (Lambdac.children()[1].pid() == sign * 3222 && Lambdac.children()[0].pid() == 331) {
      baryon1 = Lambdac.children()[1];
      imeson = 2;
    }
    else
      continue;
    Particle baryon2;
    if (baryon1.children()[0].pid() == sign * 2212 && baryon1.children()[1].pid() == 111) {
      baryon2 = baryon1.children()[0];
    }
    else if (baryon1.children()[1].pid() == sign * 2212 && baryon1.children()[0].pid() == 111) {
      baryon2 = baryon1.children()[1];
    }
    else
      continue;
    // first boost to the Lambdac rest frame
    LorentzTransform boost1 = LorentzTransform::mkFrameTransformFromBeta(Lambdac.momentum().betaVec());
    FourMomentum pbaryon1 = boost1.transform(baryon1.momentum());
    FourMomentum pbaryon2 = boost1.transform(baryon2.momentum());
    // to sigma+ 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);
    _h[imeson]->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() {
  pair<double, double> aSigma(-.983, 0.013);
  for (unsigned int ix = 0; ix < 3; ++ix) {
    normalize(_h[ix]);
    Estimate0DPtr _h_alpha1;
    book(_h_alpha1, 1, 1 + ix, 1);
    pair<double, double> alpha = calcAlpha(_h[ix]);
    _h_alpha1->set(alpha.first, alpha.second);
    // divide out alpha Sigma
    alpha.second = alpha.first / aSigma.first
        * sqrt(sqr(alpha.second / alpha.first) + sqr(aSigma.second / aSigma.first));
    alpha.first /= aSigma.first;
    Estimate0DPtr _h_alpha2;
    book(_h_alpha2, 1, 1 + ix, 2);
    _h_alpha2->set(alpha.first, alpha.second);
  }
}

/// @}


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

};

RIVET_DECLARE_PLUGIN(BELLE_2022_I2140379);

} ```