Rivet analyses

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

namespace Rivet {


  /// @brief Bs0 -> Ds* Ds*
  class BELLE_2013_I1124584 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BELLE_2013_I1124584);


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

    /// Book histograms and initialise projections before the run
    void init() {
      // Initialise and register projections
      UnstableParticles ufs = UnstableParticles(Cuts::abspid == 531);
      declare(ufs, "UFS");
      // histograms
      for (unsigned int ix = 0; ix < 2; ++ix) book(_h[ix], 1, 1, 1 + ix);
    }


    /// Perform the per-event analysis
    void analyze(const Event& event) {
      Particles BS0 = apply<UnstableParticles>(event, "UFS").particles();
      for (const Particle& p : BS0) {
        if (p.children().size() != 2) continue;
        if (p.children()[0].pid() != -p.children()[1].pid()) continue;
        if (p.children()[0].abspid() != 433) continue;
        Particle Dp = p.children()[0];
        Particle Dm = p.children()[1];
        if (p.pid() > 0 && Dp.pid() < 0)
          swap(Dp, Dm);
        else if (p.pid() < 0 && Dp.pid() > 0)
          swap(Dp, Dm);
        // boost to rest frame
        LorentzTransform boostB = LorentzTransform::mkFrameTransformFromBeta(p.momentum().betaVec());
        FourMomentum pB = boostB.transform(p.momentum());
        if (Dp.children().size() == 2) {
          Particle gamma;
          bool found = true;
          if (Dp.children()[0].pid() == PID::GAMMA && Dp.children()[1].abspid() == 431)
            gamma = Dp.children()[0];
          else if (Dp.children()[1].pid() == PID::GAMMA && Dp.children()[0].abspid() == 431)
            gamma = Dp.children()[1];
          else
            found = false;
          if (found) {
            FourMomentum pD = boostB.transform(Dp.momentum());
            FourMomentum pgamma = boostB.transform(gamma.momentum());
            LorentzTransform boostD = LorentzTransform::mkFrameTransformFromBeta(pD.betaVec());
            Vector3 axisB = boostD.transform(pB).p3().unit();
            Vector3 axisG = boostD.transform(pgamma).p3().unit();
            _h[0]->fill(axisB.dot(axisG));
          }
        }
        if (Dm.children().size() == 2) {
          Particle gamma;
          bool found = true;
          if (Dm.children()[0].pid() == PID::GAMMA && Dm.children()[1].abspid() == 431)
            gamma = Dm.children()[0];
          else if (Dm.children()[1].pid() == PID::GAMMA && Dm.children()[0].abspid() == 431)
            gamma = Dm.children()[1];
          else
            found = false;
          if (found) {
            FourMomentum pD = boostB.transform(Dm.momentum());
            FourMomentum pgamma = boostB.transform(gamma.momentum());
            LorentzTransform boostD = LorentzTransform::mkFrameTransformFromBeta(pD.betaVec());
            Vector3 axisB = boostD.transform(pB).p3().unit();
            Vector3 axisG = boostD.transform(pgamma).p3().unit();
            _h[1]->fill(axisB.dot(axisG));
          }
        }
      }
    }


    /// 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(BELLE_2013_I1124584);

}