Rivet analyses

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

namespace Rivet {


  /// @brief B0 -> D*0 omega
  class BABAR_2011_I920989 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BABAR_2011_I920989);


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

    /// Book histograms and initialise projections before the run
    void init() {
      // projection
      UnstableParticles ufs = UnstableParticles(Cuts::abspid == 511);
      declare(ufs, "UFS");
      // histos
      for (unsigned int ix = 0; ix < 4; ++ix)
        for (unsigned int iy = 0; iy < 2; ++iy) book(_h[ix][iy], 1, 1 + ix, 1 + iy);
    }

    void findChildren(const Particle& p,
                      Particles& pim,
                      Particles& pip,
                      Particles& pi0,
                      unsigned int& ncount) {
      for (const Particle& child : p.children()) {
        if (child.pid() == PID::PIPLUS) {
          pip.push_back(child);
          ncount += 1;
        }
        else if (child.pid() == PID::PIMINUS) {
          pim.push_back(child);
          ncount += 1;
        }
        else if (child.pid() == PID::PI0) {
          pi0.push_back(child);
          ncount += 1;
        }
        else if (child.children().empty()) {
          ncount += 1;
        }
        else
          findChildren(child, pim, pip, pi0, ncount);
      }
    }

    /// Perform the per-event analysis
    void analyze(const Event& event) {
      for (const Particle& B0 : apply<UnstableParticles>(event, "UFS").particles()) {
        if (B0.children().size() != 2) continue;
        Particle Dstar, omega;
        if (B0.children()[0].abspid() == 423 && B0.children()[1].pid() == 223) {
          Dstar = B0.children()[0];
          omega = B0.children()[1];
        }
        else if (B0.children()[1].abspid() == 423 && B0.children()[0].pid() == 223) {
          Dstar = B0.children()[1];
          omega = B0.children()[0];
        }
        else
          continue;
        // check the no of decay products
        if (Dstar.children().size() != 2 || omega.children().size() != 3) continue;
        // find the children of the D* meson
        Particle D0;
        if (Dstar.children()[0].pid() == 111 && Dstar.children()[1].abspid() == 421)
          D0 = Dstar.children()[1];
        else if (Dstar.children()[1].pid() == 111 && Dstar.children()[0].abspid() == 421)
          D0 = Dstar.children()[0];
        else
          continue;
        // children of the omega
        unsigned int ncount = 0;
        Particles pip, pim, pi0;
        findChildren(omega, pim, pip, pi0, ncount);
        if (ncount != 3 || !(pim.size() == 1 && pip.size() == 1 && pi0.size() == 1)) continue;
        // boost to B rest frame
        LorentzTransform boost1 = LorentzTransform::mkFrameTransformFromBeta(B0.momentum().betaVec());
        FourMomentum pDstar = boost1.transform(Dstar.momentum());
        FourMomentum pD0 = boost1.transform(D0.momentum());
        FourMomentum pomega = boost1.transform(omega.momentum());
        FourMomentum pPip = boost1.transform(pip[0].momentum());
        FourMomentum pPim = boost1.transform(pim[0].momentum());
        // boost to D* frame
        LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(pDstar.betaVec());
        pD0 = boost2.transform(pD0);
        double c1 = pD0.p3().unit().dot(pDstar.p3().unit());
        // boost to omega frame
        LorentzTransform boost3 = LorentzTransform::mkFrameTransformFromBeta(pomega.betaVec());
        pPip = boost3.transform(pPip);
        pPim = boost3.transform(pPim);
        Vector3 axisOmega = pPip.p3().cross(pPim.p3()).unit();
        double c2 = pomega.p3().unit().dot(axisOmega);
        for (unsigned int ix = 0; ix < 4; ++ix) {
          _h[ix][0]->fill(c1);
          _h[ix][1]->fill(c2);
        }
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      for (unsigned int ix = 0; ix < 4; ++ix)
        for (unsigned int iy = 0; iy < 2; ++iy) normalize(_h[ix][iy], 1., false);
    }

    /// @}


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


  RIVET_DECLARE_PLUGIN(BABAR_2011_I920989);

}