Rivet analyses

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

namespace Rivet {


  /// @brief D_s1 decay angles
  class BABAR_2011_I892421 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(BABAR_2011_I892421);


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

    /// Book histograms and initialise projections before the run
    void init() {
      // projections
      declare(UnstableParticles(), "UFS");
      // book histos
      book(_h_cP, 1, 1, 1);
      book(_h_c, 2, 1, 1);
    }

    bool isK0(int id) {
      return id == 310 || id == 130 || abs(id) == 311;
    }

    /// Perform the per-event analysis
    void analyze(const Event& event) {
      static const int DsID = 10433;
      const UnstableParticles& ufs = apply<UnstableParticles>(event, "UFS");
      for (const Particle& p : ufs.particles(Cuts::abspid == DsID)) {
        // decay angle
        int sign = p.pid() / DsID;
        Particle Dstar;
        if (p.children().size() != 2) continue;
        if (p.children()[0].pid() == sign * 413 && isK0(p.children()[1].pid())) {
          Dstar = p.children()[0];
        }
        else if (p.children()[1].pid() == sign * 413 && isK0(p.children()[0].pid())) {
          Dstar = p.children()[1];
        }
        else {
          continue;
        }
        // first boost to the D_s1 rest frame
        LorentzTransform boost1 = LorentzTransform::mkFrameTransformFromBeta(p.momentum().betaVec());
        FourMomentum pDstar = boost1.transform(Dstar.momentum());
        double cTheta = pDstar.p3().unit().dot(p.momentum().p3().unit());
        _h_c->fill(cTheta);
        if (Dstar.children().size() != 2) continue;
        Particle D0;
        if (Dstar.children()[0].pid() == sign * 211 && Dstar.children()[1].pid() == sign * 421) {
          D0 = Dstar.children()[1];
        }
        else if (Dstar.children()[1].pid() == sign * 211 && Dstar.children()[0].pid() == sign * 421) {
          D0 = Dstar.children()[0];
        }
        else
          continue;
        // boost to D_s frame
        FourMomentum pD = boost1.transform(D0.momentum());
        // to D* rest frame
        LorentzTransform boost2 = LorentzTransform::mkFrameTransformFromBeta(pDstar.betaVec());
        Vector3 axis = pDstar.p3().unit();
        FourMomentum pp = boost2.transform(pD);
        // calculate angle
        double cThetap = pp.p3().unit().dot(axis);
        _h_cP->fill(cThetap);
      }
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      normalize(_h_cP);
      normalize(_h_c);
    }

    /// @}


    /// @name Histograms
    /// @{
    Histo1DPtr _h_cP, _h_c;
    /// @}
  };


  RIVET_DECLARE_PLUGIN(BABAR_2011_I892421);

}