Rivet analyses

// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {


  /// @brief Lambda_c -> Lambda0 or Sigma0 + (pi,K)+ decay asymmetries
  class BELLE_2022_I2138841 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BELLE_2022_I2138841);


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

    /// Book histograms and initialise projections before the run
    void init() {
      // Initialise and register projections
      declare(UnstableParticles(), "UFS");
      for (unsigned int imode = 0; imode < 4; ++imode) {
        if (imode < 2) {
          book(_h[imode][0], 3, 1, 1 + imode);
          for (unsigned int iy = 0; iy < 2; ++iy) {
            book(_h[imode][1 + iy], 4, 1, 1 + iy + 2 * imode);
          }
        }
        for (unsigned int iy = 0; iy < 3; ++iy) {
          for (unsigned int iz = 0; iz < 2; ++iz) {
            book(_c[imode][iy][iz],
                 "TMP/C_" + toString(imode + 1) + "_" + toString(iy + 1) + "_" + toString(iz + 1));
          }
        }
      }
    }

    /// 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 * 3122 || Lambdac.children()[0].pid() == sign * 3212)
            && Lambdac.children()[1].pid() == sign * 321) {
          baryon1 = Lambdac.children()[0];
          imeson = 0;
        }
        else if ((Lambdac.children()[1].pid() == sign * 3122 || Lambdac.children()[0].pid() == sign * 3212)
                 && Lambdac.children()[0].pid() == sign * 321) {
          baryon1 = Lambdac.children()[1];
          imeson = 0;
        }
        else if ((Lambdac.children()[0].pid() == sign * 3122 || Lambdac.children()[0].pid() == sign * 3212)
                 && Lambdac.children()[1].pid() == sign * 211) {
          baryon1 = Lambdac.children()[0];
          imeson = 1;
        }
        else if ((Lambdac.children()[1].pid() == sign * 3122 || Lambdac.children()[0].pid() == sign * 3212)
                 && Lambdac.children()[0].pid() == sign * 211) {
          baryon1 = Lambdac.children()[1];
          imeson = 1;
        }
        else {
          continue;
        }
        // Lambda0 case
        if (baryon1.abspid() == 3122) {
          Particle baryon2;
          if (baryon1.children()[0].pid() == sign * 2212 && baryon1.children()[1].pid() == -sign * 211) {
            baryon2 = baryon1.children()[0];
          }
          else if (baryon1.children()[1].pid() == sign * 2212 && baryon1.children()[0].pid() == -sign * 211) {
            baryon2 = baryon1.children()[1];
          }
          else {
            continue;
          }
          // first boost to the Lambdac rest frame
          LorentzTransform boost1 = LorentzTransform::mkFrameTransformFromBeta(Lambdac.mom().betaVec());
          FourMomentum pbaryon1 = boost1.transform(baryon1.mom());
          FourMomentum pbaryon2 = boost1.transform(baryon2.mom());
          // 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);
          _h[imeson][0]->fill(cTheta);
          _c[imeson][0][0]->fill();
          _c[imeson][0][1]->fill(3. * cTheta);
          if (baryon1.pid() > 0) {
            _h[imeson][1]->fill(cTheta);
            _c[imeson][1][0]->fill();
            _c[imeson][1][1]->fill(3. * cTheta);
          }
          else {
            _h[imeson][2]->fill(cTheta);
            _c[imeson][2][0]->fill();
            _c[imeson][2][1]->fill(3. * cTheta);
          }
        }
        // sigma0 case
        else {
          Particle baryon2;
          if (baryon1.children()[0].pid() == sign * 3122 && baryon1.children()[1].pid() == 22) {
            baryon2 = baryon1.children()[0];
          }
          else if (baryon1.children()[1].pid() == sign * 3122 && baryon1.children()[0].pid() == 22) {
            baryon2 = baryon1.children()[1];
          }
          else {
            continue;
          }
          Particle baryon3;
          if (baryon2.children()[0].pid() == sign * 2212 && baryon2.children()[1].pid() == -sign * 211) {
            baryon3 = baryon2.children()[0];
          }
          else if (baryon2.children()[1].pid() == sign * 2212 && baryon2.children()[0].pid() == -sign * 211) {
            baryon3 = baryon2.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());
          FourMomentum pbaryon3 = boost1.transform(baryon3.momentum());
          // to  sigma rest frame
          LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(pbaryon1.betaVec());
          Vector3 axis = pbaryon1.p3().unit();
          FourMomentum pp = boost2.transform(pbaryon2);
          FourMomentum pp3 = boost2.transform(pbaryon3);
          // calculate angle
          double cTheta2 = pp.p3().unit().dot(axis);
          // to lambda rest frame
          LorentzTransform boost3 = LorentzTransform::mkFrameTransformFromBeta(pp.betaVec());
          Vector3 axis2 = pp.p3().unit();
          FourMomentum pp4 = boost3.transform(pp3);
          // calculate angle
          double cTheta3 = pp4.p3().unit().dot(axis2);
          double cTheta = cTheta2 * cTheta3;
          _c[imeson + 2][0][0]->fill();
          _c[imeson + 2][0][1]->fill(-9. * cTheta);
          if (baryon1.pid() > 0) {
            _c[imeson + 2][1][0]->fill();
            _c[imeson + 2][1][1]->fill(-9. * cTheta);
          }
          else {
            _c[imeson + 2][2][0]->fill();
            _c[imeson + 2][2][1]->fill(-9. * cTheta);
          }
        }
      }
    }

    /// Normalise histograms etc., after the run
    void finalize() {
      pair<double, double> aLambda(0.7542, 0.0022);
      for (int imeson = 0; imeson < 4; ++imeson) {
        for (int iy = 0; iy < 3; ++iy) {
          if (imeson < 2) normalize(_h[imeson][iy]);
          Estimate0DPtr _h_alpha1, _h_alpha2;
          if (iy == 0) {
            book(_h_alpha1, 1, 1 + imeson, 1);
            book(_h_alpha2, 1, 1 + imeson, 2);
          }
          else {
            book(_h_alpha1, 2, 1 + imeson, iy);
            book(_h_alpha2, 2, 1 + imeson, 2 + iy);
          }
          if (_c[imeson][iy][0]->val() == 0.) continue;
          divide(_c[imeson][iy][1], _c[imeson][iy][0], _h_alpha1);
          // divide out aLambda
          double rval = _h_alpha1->val() / aLambda.first;
          pair<double, double> rerr = _h_alpha1->err();
          rerr.first = sqrt(sqr(rerr.first / rval) + sqr(aLambda.second / aLambda.first));
          rerr.second = sqrt(sqr(rerr.second / rval) + sqr(aLambda.second / aLambda.first));
          rerr.first *= rval;
          rerr.second *= rval;
          if (iy == 2) {
            rval *= -1;
            swap(rerr.first, rerr.second);
          }
          _h_alpha2->set(rval, rerr);
        }
      }
    }

    /// @}


    /// @name Histograms
    /// @{
    Histo1DPtr _h[2][3];
    CounterPtr _c[4][3][2];
    /// @}
  };


  RIVET_DECLARE_PLUGIN(BELLE_2022_I2138841);

}