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);

}