Rivet analyses

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

namespace Rivet {


  /// @brief B0 -> D*+ D*-
  class BELLE_2012_I1123656 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BELLE_2012_I1123656);


    /// @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");
      // 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 B0 = apply<UnstableParticles>(event, "UFS").particles();
      for (const Particle& p : B0) {
        if (p.children().size() != 2) continue;
        if (p.children()[0].pid() != -p.children()[1].pid()) continue;
        if (p.children()[0].abspid() != 413) 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);
        // find children of the D mesons
        Particle pip, pim;
        if (Dp.children().size() != 2) continue;
        if (Dp.children()[0].abspid() == PID::PIPLUS && Dp.children()[1].abspid() == PID::D0)
          pip = Dp.children()[0];
        else if (Dp.children()[1].abspid() == PID::PIPLUS && Dp.children()[0].abspid() == PID::D0)
          pip = Dp.children()[1];
        else
          continue;
        if (Dm.children().size() != 2) continue;
        if (Dm.children()[0].abspid() == PID::PIPLUS && Dm.children()[1].abspid() == PID::D0) {
          pim = Dm.children()[0];
        }
        else if (Dm.children()[1].abspid() == PID::PIPLUS && Dm.children()[0].abspid() == PID::D0) {
          pim = Dm.children()[1];
        }
        else
          continue;
        // boost to rest frame
        LorentzTransform boostB = LorentzTransform::mkFrameTransformFromBeta(p.momentum().betaVec());
        FourMomentum pDstarPlus = boostB.transform(Dp.momentum());
        FourMomentum pDstarMinus = boostB.transform(Dm.momentum());
        LorentzTransform boostDp = LorentzTransform::mkFrameTransformFromBeta(pDstarPlus.betaVec());
        FourMomentum ppip = boostDp.transform(boostB.transform(pip.momentum()));
        LorentzTransform boostDm = LorentzTransform::mkFrameTransformFromBeta(pDstarMinus.betaVec());
        FourMomentum ppim = boostDm.transform(boostB.transform(pim.momentum()));
        Vector3 axisX = pDstarPlus.p3().unit();
        // ctheta1
        _h[1]->fill(axisX.dot(ppim.p3().unit()));
        // y and z axis
        ppim = boostDp.transform(boostB.transform(pim.momentum()));
        Vector3 axisZ = axisX.cross(ppim.p3()).unit();
        // cThetaTr
        _h[0]->fill(axisZ.dot(ppip.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(BELLE_2012_I1123656);

}