Rivet analyses

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

namespace Rivet {


  /// @brief B+ -> omega rho+
  class BABAR_2005_I664717 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BABAR_2005_I664717);


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

    /// Book histograms and initialise projections before the run
    void init() {
      // Initialise and register projections
      UnstableParticles ufs = UnstableParticles(Cuts::abspid == 521);
      declare(ufs, "UFS");
      DecayedParticles BP(ufs);
      BP.addStable(213);
      BP.addStable(-213);
      BP.addStable(223);
      declare(BP, "BP");
      // histos
      for (unsigned int ix = 0; ix < 2; ++ix) book(_h[ix], 1, 1, 1 + ix);
    }

    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) {
      static const map<PdgId, unsigned int>& mode = {{223, 1}, {213, 1}};
      static const map<PdgId, unsigned int>& modeCC = {{223, 1}, {-213, 1}};
      DecayedParticles BP = apply<DecayedParticles>(event, "BP");
      // loop over particles
      for (unsigned int ix = 0; ix < BP.decaying().size(); ++ix) {
        if (BP.modeMatches(ix, 2, mode) || BP.modeMatches(ix, 2, modeCC)) {
          const Particle& omega = BP.decayProducts()[ix].at(223)[0];
          // 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;
          // rho decay
          int sign = BP.decaying()[ix].pid() / BP.decaying()[ix].abspid();
          const Particle& rho = BP.decayProducts()[ix].at(sign * 213)[0];
          if (rho.children().size() != 2) continue;
          Particle pi;
          if (rho.children()[0].pid() == sign * 211 && rho.children()[1].pid() == 111)
            pi = rho.children()[0];
          else if (rho.children()[1].pid() == sign * 211 && rho.children()[0].pid() == 111)
            pi = rho.children()[1];
          else
            continue;
          // boosts
          LorentzTransform boost1 = LorentzTransform::mkFrameTransformFromBeta(
              BP.decaying()[ix].momentum().betaVec());
          FourMomentum pomega = boost1.transform(omega.momentum());
          FourMomentum prho = boost1.transform(rho.momentum());
          FourMomentum pPip = boost1.transform(pip[0].momentum());
          FourMomentum pPim = boost1.transform(pim[0].momentum());
          FourMomentum pPi = boost1.transform(pi.momentum());
          // boost to omega frame
          LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(pomega.betaVec());
          pPip = boost2.transform(pPip);
          pPim = boost2.transform(pPim);
          Vector3 axisOmega = pPip.p3().cross(pPim.p3()).unit();
          // helicity angle
          _h[0]->fill(abs(pomega.p3().unit().dot(axisOmega)));
          // boost to rho rest frame
          LorentzTransform boost3 = LorentzTransform::mkFrameTransformFromBeta(prho.betaVec());
          pPi = boost3.transform(pPi);
          _h[1]->fill(prho.p3().unit().dot(pPi.p3().unit()));
        }
      }
    }


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

    /// @}


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


  RIVET_DECLARE_PLUGIN(BABAR_2005_I664717);

}