Rivet analyses

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

namespace Rivet {


  /// @brief B -> K* J/psi, psi(2S) and chi_c1
  class BABAR_2007_I748372 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BABAR_2007_I748372);


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

    /// Book histograms and initialise projections before the run
    void init() {
      // Initialise and register projections
      UnstableParticles ufs = UnstableParticles(Cuts::abspid == 511 or Cuts::abspid == 521);
      declare(ufs, "UFS");
      // histograms
      for (unsigned int ix = 0; ix < 3; ++ix)
        for (unsigned int iy = 0; iy < 3; ++iy)
          for (unsigned int iz = 0; iz < 3; ++iz) book(_h[ix][iy][iz], 1 + ix, 1 + iy, 1 + iz);
    }

    bool isOnium(int pid) const {
      return pid == 443 || pid == 100443 || pid == 20443;
    }

    bool isKstar(int pid) const {
      return pid == 313 || pid == 323;
    }

    bool isK(int pid) const {
      return pid == 130 || pid == 310 || pid == 311 || pid == 321;
    }

    bool isPi(int pid) const {
      return pid == 211 || pid == 111;
    }

    /// Perform the per-event analysis
    void analyze(const Event& event) {
      UnstableParticles ufs = apply<UnstableParticles>(event, "UFS");
      for (const Particle& B : ufs.particles()) {
        if (B.children().size() != 2) continue;
        Particle onium, Kstar;
        if (isOnium(B.children()[0].abspid()) && isKstar(B.children()[1].abspid())) {
          onium = B.children()[0];
          Kstar = B.children()[1];
        }
        else if (isOnium(B.children()[1].abspid()) && isKstar(B.children()[0].abspid())) {
          onium = B.children()[1];
          Kstar = B.children()[0];
        }
        else
          continue;
        if (onium.children().size() != 2) continue;
        // find Kstar decay products
        Particle K;
        if (isK(Kstar.children()[0].abspid()) && isPi(Kstar.children()[1].abspid())) {
          K = Kstar.children()[0];
        }
        else if (isK(Kstar.children()[1].abspid()) && isPi(Kstar.children()[0].abspid())) {
          K = Kstar.children()[1];
        }
        else
          continue;
        int iK = -1;
        if (B.abspid() == 511) {
          if (K.abspid() == 321)
            iK = 0;
          else
            continue;
        }
        else {
          if (K.abspid() == 321)
            iK = 2;
          else
            iK = 1;
        }
        // find onium decay products
        Particle oDec;
        if (onium.pid() == 20443) {
          if (onium.children()[0].pid() == 443 && onium.children()[1].pid() == 22) {
            oDec = onium.children()[0];
          }
          else if (onium.children()[1].pid() == 443 && onium.children()[0].pid() == 22) {
            oDec = onium.children()[1];
          }
          else
            continue;
        }
        else {
          if (onium.children()[0].pid() == -13 && onium.children()[1].pid() == 13) {
            oDec = onium.children()[1];
          }
          else if (onium.children()[1].pid() == -13 && onium.children()[0].pid() == 13) {
            oDec = onium.children()[0];
          }
          else if (onium.children()[0].pid() == -11 && onium.children()[1].pid() == 11) {
            oDec = onium.children()[1];
          }
          else if (onium.children()[1].pid() == -11 && onium.children()[0].pid() == 11) {
            oDec = onium.children()[0];
          }
          else
            continue;
        }
        // boost to B rest frame
        LorentzTransform boost = LorentzTransform::mkFrameTransformFromBeta(B.momentum().betaVec());
        FourMomentum pOnium = boost.transform(onium.momentum());
        FourMomentum pKstar = boost.transform(Kstar.momentum());
        FourMomentum pK = boost.transform(K.momentum());
        FourMomentum pOdec = boost.transform(oDec.momentum());
        // axes
        Vector3 axisX = pOnium.p3().unit();
        Vector3 axisY = (pK.p3() - axisX.dot(pK.p3()) * axisX).unit();
        Vector3 axisZ = axisX.cross(axisY).unit();
        // kaon helicity angle
        LorentzTransform boostK = LorentzTransform::mkFrameTransformFromBeta(pKstar.betaVec());
        double cosK = -axisX.dot(boostK.transform(pK).p3().unit());
        // transversality angles
        LorentzTransform boostL = LorentzTransform::mkFrameTransformFromBeta(pOnium.betaVec());
        Vector3 axisL = boostL.transform(pOdec).p3().unit();
        double cosL = axisL.dot(axisZ);
        double phiL = atan2(axisL.dot(axisY), axisL.dot(axisX));
        if (phiL < 0.) phiL += 2. * M_PI;
        // fill hists
        int iloc = onium.pid() == 443 ? 0 : (onium.pid() == 100443 ? 1 : 2);
        _h[0][iloc][iK]->fill(cosK);
        _h[1][iloc][iK]->fill(cosL);
        _h[2][iloc][iK]->fill(phiL);
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      for (unsigned int ix = 0; ix < 3; ++ix)
        for (unsigned int iy = 0; iy < 3; ++iy)
          for (unsigned int iz = 0; iz < 3; ++iz) normalize(_h[ix][iy][iz], 1., false);
    }

    /// @}


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


  RIVET_DECLARE_PLUGIN(BABAR_2007_I748372);

}