Rivet analyses

title: BABAR_2008_I781294

Decay asymmetries in the decay of $\Xi^*(1530)^0$ baryons produced in the decay of $\Lambda_c^+$ baryons

Experiment: BABAR (PEP-II)

Inspire ID: 781294

Status: VALIDATED

Authors: - Peter Richardson

References: - Phys.Rev.D 78 (2008) 034008

Beams: * *

Beam energies: ANY

Run details: - Any process producing Lambda_c+ baryons

Measurement of decay asymmetries in $\Lambda_c^+\to\Xi^(1530)^0K^+$ followed by $\Xi^(1530)^0\Xi^-\pi+$ decays by the BaBaR experiment.

Source code:BABAR_2008_I781294.cc

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

include "Rivet/Analysis.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief Xi* decay asymmetries class BABAR_2008_I781294 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BABAR_2008_I781294);


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

/// Book histograms and initialise projections before the run
void init() {
  // Initialise and register projections
  declare(UnstableParticles(), "UFS");
  // book histos
  book(_h_ctheta, 1, 1, 1);
  book(_h_P0, 2, 1, 1);
  book(_h_P2, 2, 1, 2);
  book(_wgtSum, "/TMP/WSUM");
}

void findChildren(const Particle& p,
                  int& sign,
                  unsigned int& nprod,
                  Particles& Xi,
                  Particles& pi,
                  Particles& K) {
  for (const Particle& child : p.children()) {
    if (child.pid() == sign * 3312) {
      Xi.push_back(child);
      ++nprod;
    }
    else if (child.pid() == 211) {
      pi.push_back(child);
      ++nprod;
    }
    else if (child.pid() == 321) {
      K.push_back(child);
      ++nprod;
    }
    else if (child.children().empty()) {
      ++nprod;
    }
    else {
      findChildren(child, sign, nprod, Xi, pi, K);
    }
  }
}

/// Perform the per-event analysis
void analyze(const Event& event) {
  // loop over Lambda_c
  for (const Particle& baryon : apply<UnstableParticles>(event, "UFS").particles(Cuts::abspid == 4122)) {
    int sign = baryon.pid() / baryon.abspid();
    Particles Xi, pi, K;
    unsigned int nprod(0);
    findChildren(baryon, sign, nprod, Xi, pi, K);
    // check Lambda_c -> Xi- pi+ K+ decya mode
    if (nprod != 3 || Xi.size() != 1 || pi.size() != 1 || K.size() != 1) continue;
    // first boost to the Lambda_c rest frame
    LorentzTransform boost1 = LorentzTransform::mkFrameTransformFromBeta(baryon.momentum().betaVec());
    FourMomentum pbaryon1 = Xi[0].momentum() + pi[0].momentum();
    pbaryon1 = boost1.transform(pbaryon1);
    FourMomentum pbaryon2 = boost1.transform(Xi[0].momentum());
    // to Xi* 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);
    double mass = pbaryon1.mass();
    if (mass > 1.5 && mass < 1.65) _h_ctheta->fill(cTheta);
    _h_P0->fill(mass);
    _h_P2->fill(mass, 0.5 * (3. * sqr(cTheta) - 1.));
    _wgtSum->fill();
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  normalize(_h_ctheta);
  normalize(_h_P0, 1., false);
  normalize(_h_P2, 1., false);
}
/// @}


/// @name Histograms
/// @{
Histo1DPtr _h_ctheta, _h_P0, _h_P2;
CounterPtr _wgtSum;
/// @}

};

RIVET_DECLARE_PLUGIN(BABAR_2008_I781294);

} ```