Rivet analyses

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

namespace Rivet {


  /// @brief B* production at LEP1
  class OPAL_1996_I428493 : public Analysis {
  public:

    /// Constructor
    RIVET_DEFAULT_ANALYSIS_CTOR(OPAL_1996_I428493);


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

    /// Book histograms and initialise projections before the run
    void init() {

      // // Initialise and register projections
      declare(ChargedFinalState(), "FS");
      declare(UnstableParticles(), "UFS");

      // Book histograms
      book(_h_ctheta1, 3,1,1);
      book(_h_ctheta2, "/TMP/ctheta",20,-1.,1.);
      book(_c_hadron , "/TMP/chadron");
      book(_c_bStar  , "/TMP/cbStar ", refData<YODA::BinnedEstimate<string>>(1,1,1));
      book(_c_B      , "/TMP/cB     ", refData<YODA::BinnedEstimate<string>>(1,1,1));
    }


    /// Perform the per-event analysis
    void analyze(const Event& event) {
      // First, veto on leptonic events by requiring at least 4 charged FS particles
      const FinalState& fs = apply<FinalState>(event, "FS");
      const size_t numParticles = fs.particles().size();

      // Even if we only generate hadronic events, we still need a cut on numCharged >= 2.
      if (numParticles < 2) {
        MSG_DEBUG("Failed leptonic event cut");
        vetoEvent;
      }
      MSG_DEBUG("Passed leptonic event cut");

      _c_hadron->fill();
      // loop over the particles
      for(const Particle& p : apply<UnstableParticles>(event, "UFS").particles(Cuts::abspid==513 or Cuts::abspid==523 or
                                           Cuts::abspid==511 or Cuts::abspid==521)) {
    int sign = p.pid()/p.abspid();
    // count number of Bs not from mixing or B*
    if(p.abspid()==511 || p.abspid()==521) {
      if(p.parents()[0].abspid()==p.abspid()) continue;
      if(p.parents()[0].abspid()==513 || p.parents()[0].abspid()==523) continue;
      _c_B->fill("91.2"s);
    }
    // B*
    else {
      _c_bStar->fill("91.2"s);
      Particle decay;
      if(p.children().size()!=2) continue;
      int mid = p.abspid()-2;
      if(p.children()[0].pid()==sign*mid &&
         p.children()[1].pid()==22) {
        decay = p.children()[1];
      }
      else if(p.children()[1].pid()==sign*mid &&
          p.children()[0].pid()==22) {
        decay = p.children()[0];
      }
      else
        continue;
      LorentzTransform boost = LorentzTransform::mkFrameTransformFromBeta(p.momentum().betaVec());
      Vector3 e1z = p.p3().unit();
      FourMomentum pp = boost.transform(decay.momentum());
      Vector3 axis1 = boost.transform(decay.momentum()).p3().unit();
      double ctheta = e1z.dot(axis1);
      _h_ctheta1->fill(ctheta);
      _h_ctheta2->fill(ctheta);
    }
      }
    }

    pair<double,double> calcRho(Histo1DPtr hist) {
      if(hist->numEntries()==0.) return make_pair(0.,0.);
      double sum1(0.),sum2(0.);
      for (const auto& bin : hist->bins() ) {
    double Oi = bin.sumW();
    if(Oi==0.) continue;
    double ai = 0.125*( -bin.xMin()*(3.+sqr(bin.xMin())) + bin.xMax()*(3.+sqr(bin.xMax())));
    double bi = 0.375*( -bin.xMin()*(1.-sqr(bin.xMin())) + bin.xMax()*(1.-sqr(bin.xMax())));
    double Ei = bin.errW();
    sum1 += sqr(bi/Ei);
    sum2 += bi/sqr(Ei)*(Oi-ai);
      }
      return make_pair(sum2/sum1,sqrt(1./sum1));
    }


    /// Normalise histograms etc., after the run
    void finalize() {
      // polarization
      scale(_h_ctheta1,1./_c_hadron->val());
      normalize(_h_ctheta2);
      pair<double,double> rho = calcRho(_h_ctheta2);
      BinnedEstimatePtr<string> h_rho;
      book(h_rho,2,1,1);
      h_rho->bin(1).set(rho.first, rho.second);
      BinnedEstimatePtr<string> h1;
      book(h1, 1,1,1);
      // no of B*/B+B*
      divide(*_c_bStar,*_c_bStar + *_c_B, h1);
    }

    /// @}


    /// @name Histograms
    /// @{
    Histo1DPtr _h_ctheta1, _h_ctheta2;
    CounterPtr _c_hadron;
    BinnedHistoPtr<string> _c_bStar,_c_B;
    /// @}


  };


  RIVET_DECLARE_PLUGIN(OPAL_1996_I428493);


}