Rivet analyses

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

namespace Rivet {


  /// @brief B0 -> phi K*
  class BELLE_2013_I1247059 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BELLE_2013_I1247059);


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

    /// Book histograms and initialise projections before the run
    void init() {
      // Initialise and register projections
      UnstableParticles ufs = UnstableParticles(Cuts::abspid == 511);
      declare(ufs, "UFS");
      DecayedParticles B0(ufs);
      B0.addStable(333);
      declare(B0, "B0");
      // histograms
      for (unsigned int ix = 0; ix < 4; ++ix) book(_h[ix], 1, 1, 1 + ix);
    }


    /// Perform the per-event analysis
    void analyze(const Event& event) {
      static const map<PdgId, unsigned int>& mode = {{321, 1}, {-211, 1}, {333, 1}};
      static const map<PdgId, unsigned int>& modeCC = {{-321, 1}, {211, 1}, {333, 1}};
      DecayedParticles B0 = apply<DecayedParticles>(event, "B0");
      // loop over particles
      for (unsigned int ix = 0; ix < B0.decaying().size(); ++ix) {
        int sign = 1;
        if (B0.decaying()[ix].pid() > 0 && B0.modeMatches(ix, 3, mode)) {
          sign = 1;
        }
        else if (B0.decaying()[ix].pid() < 0 && B0.modeMatches(ix, 3, modeCC)) {
          sign = -1;
        }
        else
          continue;
        const Particle& Kp = B0.decayProducts()[ix].at(321 * sign)[0];
        const Particle& pim = B0.decayProducts()[ix].at(-211 * sign)[0];
        const Particle& phi = B0.decayProducts()[ix].at(333)[0];
        if (phi.children().size() != 2 || phi.children()[0].pid() != -phi.children()[1].pid()
            || phi.children()[0].abspid() != 321)
          continue;
        Particle Kp1 = phi.children()[0];
        Particle Km1 = phi.children()[1];
        if (Kp1.pid() < 0) swap(Kp1, Km1);
        // B0 frame
        LorentzTransform boost1 = LorentzTransform::mkFrameTransformFromBeta(
            B0.decaying()[ix].momentum().betaVec());
        FourMomentum pKstar = boost1.transform(Kp.momentum() + pim.momentum());
        FourMomentum pPhi = boost1.transform(phi.momentum());
        // stuff in K* frame
        LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(pKstar.betaVec());
        FourMomentum pKp = boost2.transform(boost1.transform(Kp.momentum()));
        Vector3 axis1 = pKstar.p3().unit();
        double cTheta1 = axis1.dot(pKp.p3().unit());
        if (cTheta1 > 0.75) continue;
        Vector3 trans1 = pKp.p3() - cTheta1 * pKp.p3().mod() * axis1;
        // stuff in phi frame
        LorentzTransform boost3 = LorentzTransform::mkFrameTransformFromBeta(pPhi.betaVec());
        FourMomentum pKp1 = boost3.transform(boost1.transform(Kp1.momentum()));
        Vector3 axis2 = pPhi.p3().unit();
        double cTheta2 = axis2.dot(pKp1.p3().unit());
        Vector3 trans2 = pKp1.p3() - cTheta2 * pKp1.p3().mod() * axis2;
        // angle between planes
        double chi = atan2(trans1.cross(trans2).dot(axis1), trans1.dot(trans2));
        // fill histos
        _h[0]->fill(pKstar.mass());
        _h[1]->fill(cTheta1);
        _h[2]->fill(cTheta2);
        _h[3]->fill(chi);
      }
    }


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

    /// @}


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


  RIVET_DECLARE_PLUGIN(BELLE_2013_I1247059);

}