Rivet analyses

Decay asymmetries in the decay of Ξ*(1530)0 baryons produced in the decay of Λc+ 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 Λc+ → Ξ*(1530)0K+ followed by Ξ*(1530)0Ξ−π+ decays by the BaBaR experiment.

Source code:BABAR_2008_I781294.cc

// -*- 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);

}